Project Ford Focus SVT

Project Ford Focus SVT

Former Associate Senior Editor Jared Holstein can dance like you can't believe. He can drive a car right to the edge of disaster while turning amazingly fast lap times. He's also cultured, with enough knowledge of fashion, art, music, fine food and drink to make the Queer Eye guys run for their contracts. The only problem is, he has zero mechanical sympathy and a definite knack for turning all things mechanical into a scrap heap at the drop of a hat.

Before he left SCC to expand his journalistic horizons, Holstein took our turbocharged Project Ford Focus SVT out for a spin and, as a going away present to us, did quite a number on the Zetec engine's bottom end. Because Holstein is Holstein, we forgave him for the ton of rebuilding work, as this was not an intentional act, but rather something as natural to him as, well, breaking stuff.

We learned a harsh lesson in automotive reality about the combination of a 10.2:1 compression ratio, cast pistons, a turbocharger, crappy 91-octane California gas and an on-the-fritz MAF being right on the edge. Throw in a driver with a lead foot and an apparently deaf ear towards the sound of detonation, and you get one very dead motor.A postmortem examination found completely nuked pistons. The ring lands were more than just fractured or pinched (the normal sure-fire signs of detonation damage), they were completely gone. The rings were not just stuck and scored but melted, with large spans missing. Even the skirts were melted. And it wasn't just the pistons. The block was scored so badly that it couldn't be saved, even by an enthusiastic overbore.

We had never witnessed such destruction before. Although we were left with a big repair task, we made a commitment to bring Project Focus SVT back, so that, one day, it might finally face off with a Mustang Cobra on the track. FocusSport, one of the leading tuners of the Focus platform, generously stepped forward to help us put our dead player back together.

The factory Ford Zetec engine is a high performance powerplant with a strong bottom end and a tough cast iron block. The Focus SVT version has beefed-up pistons, crank and rods. The stock internal components are usually reliable until about 280 to 300bhp. Untouched, the engine makes a respectable 170bhp with a 10.2:1 compression ratio-not a forced induction-friendly number. Not that that matters, since those pistons are now just paperweights. To give us a more forgiving margin, considering our home state's penchant for having some of the worst fuel in the nation, we decided to reduce the compression ratio to a more turbo-friendly 9:1, courtesy of some forged pistons from JE Pistons.In order to avoid terminal engine issues, we were compelled to obtain some of the toughest possible pistons. Most forged pistons are manufactured from either 2618 or 4032 aluminum alloy. Both have advantages and disadvantages, depending on application. Racing engines usually require stronger low-silicon 2618 alloy, while less demanding applications favor the greater silicon content found in 4032 alloy.

Our pistons started as blanks, forged from 2618 alloy. This alloy is extremely ductile and strong, perfect for the stress and pounding of a forced induction set-up, or dealing with Holstein. The primary disadvantage is a greater coefficient of thermal expansion. When exposed to heat, a piston made of 2618 alloy will expand approximately 13 percent more than its 4032 counterpart. To accommodate the additional expansion, more initial piston-to-wall clearance is necessary. Extra clearance results in more piston noise at cold start-up, but this effect diminishes as operating temperatures are reached.

JE Pistons' extensive engineering experience and tight manufacturing tolerances result in a precisely shaped piston skirt profile. A typical skirt profile will incorporate a 'barrel shape' (when looking at the piston side-on), with more clearance at the heat-soaked top of the piston, less mid-skirt, and an inward taper at the base. This design optimizes clearance across the skirt face, based on the location of heat. JE pistons feature some of the tightest bore clearance specifications of any low-silicon piston. The correct amount of clearance will reduce 'slap' against the cylinder walls for less wear and quieter operation. The pistons are also optimized for strength and lightness-ours weigh just 299 grams each.

We used shelf part number 185915. These pistons feature many of JE's technically advanced designs, such as double forced pin oilers, contact reduction and accumulator grooves. Contact reduction grooves are small waves machined into the contact face of the top ring land. They serve as a labyrinth baffle to help buffer shock waves caused by detonation, minimizing ring flutter and damage. This design also gives the aluminum room to expand and prevents scuffing against the cylinder wall.

The accumulator groove is possibly the most beneficial feature. This V-style groove is located on the second ring land between the top and second rings. It acts like a reservoir for high-pressure combustion gases that leak past the first ring, reducing the pressure that can lift the top ring from the base of the groove and cause it to lose its seal. This difference is most significant at high revs.

Double forced pin oilers feed the wrist pin with a steady supply of oil pumped in from the oil ring groove. Proper wrist pin lubrication is crucial, especially in engines using forced induction. The pistons also use a thick-walled, straight-diameter, high-carbon steel piston pin, a better choice to reduce flex in high-load, forced induction applications. The pin is held in place with Spiro-Locks, probably the most secure pin anchoring system available.

The top ring land is made thicker, to increase land strength and move the top ring away from the intense environment of the combustion chamber. This is the opposite strategy of the damage-prone OEM piston that features a short top ring land to reduce hydrocarbon emissions. The tops of our pistons use a 6.9cc dish to reduce compression ratio. The dish design puts flat areas of the piston top in line with the quench pads in the cylinder head. This causes turbulence in the mixture as the piston reaches top dead center, resulting in complete burn and a reduced likelihood of detonation. This type of piston top configuration is called a reverse deflector.

JE Pro Seal rings were also selected. They're significantly thinner than the OEM ring set. This design results in less radial tension, therefore less friction and more power. The thinner profile also means that the rings are lighter and less prone to inertial flutter from the base of the ring groove. Plus, they won't lose their seal at high revs. The chrome-faced top and oil rings are perfect for our iron bores.

JE makes the 185915 pistons for 85mm bore sizes. This is approximately 0.007-inch larger than the standard Zetec bore. The design incorporates a piston-to-wall clearance of 0.004-inch. Honing our bores 0.007-inch oversize to exactly 85mm is all that is necessary to prepare them properly. We handed our block to Cosworth Engineering in Torrance, California, to make use of its world-class machining facility.

To hang the pistons, we needed to find a stronger connecting rod. We chose Eagle for its ESP rods, forged from a high nickel and chromium 4340 steel alloy. The nickel and chromium give the steel a high tensile strength and a much improved fatigue resistance over regular high carbon, and even chromoly steels. A good feature is that the rod is forged in two pieces, with the cap forged separately. This allows it to have the metal's grain flow in a circle around the big end bore. With this forging method, there is greater strength and less distortion of the rod's big end under load. Typically, rods are machined from a one-piece forging, where the grain flow is along the length of the rod. When the big end of the rod is machined, the grain is interrupted by the hole.

The rod's beams are machined in an H profile. This profile is stiffer, putting more material where it is needed for strength and none elsewhere. With this sort of construction, an Eagle rod is typically about 100 grams lighter that most stock rods. In the machined valley of the H is a small rib at the base. This enhances the beam's strength.

Piston pin oiling holes are drilled upwards at an angle towards the pin. This is unlike the standard practice, where pin oiling comes from a single hole drilled at the top of the rod. This hole significantly weakens the small end of the rod. By putting two smaller holes at the bottom, at the less stressed portion of the pin boss, Eagle has a much stronger part.

The rod's entire surface is machine finished. This ensures consistency in both dimension and weight. After machining, the rod is subjected to shotpeening, a process where it is bombarded by hard steel shot at high velocities.

Shotpeening helps refine the metal's grain over the surface of the rod, creating a finely grained compressed layer of steel where cracks have a hard time propagating. Shotpeening improves fatigue resistance in most steel parts by over 100 percent.

The piston pin bushing is tough silicon bronze, one of the most wear-resistant bushing materials available. As the rod bolts are the most critical part on the connecting rod, no expense was spared. Eagle uses genuine ARP 8740 7/16-inch rod bolts for all its sport compact series. These have a tensile strength of over 230,000psi, many times stronger than the factory bolts. Altogether, each new piston, pin and rod assembly weighs 1.9 pounds. The far weaker stock components weigh 2.35 pounds.

Once the block machining was complete and the parts lined up, FocusSport assembled our motor's bottom end, making doubly sure it would hold up if Holstein ever found his way behind the wheel of Project Focus SVT again. All critical clearances were double-checked and the bearings replaced with genuine Ford parts. As the stock SVT crankshaft is a beefy fully counterweighted forged part, FocusSport retained it.

With our bulletproof bottom end cinched up, next time we'll be ready to bolt on our Cosworth cylinder head, Quaife-equipped transmission and stuff it all back into the chassis. That is, just as soon as we kill all the black widow spiders that have claimed our Focus as their home for the past two years.

Photo Gallery: Project Ford Focus SVT Pt 6 - Sport Compact Car Magazine

Read More |
Digg It |
Add to del.icio.us

For Better Or Worse

For Better Or Worse

The big news regarding the 2008 Impreza was the re-designed chassis and resulting suspension changes. Until now, though, no one really knew how the sophisticated rear multi-link system would compare to the old MacPherson strut set-up of previous generations. WRX fans have been rejoicing, because multi-link can only mean better performance; on paper, a double A-arm suspension would have an advantage in terms of camber gain. But is the new suspension really all it's cracked up to be?

We were able to take a brief look at the undercarriage of a new 2008 Impreza sedan, side-by-side with a 2007 Impreza wagon. Doing some quick measurements, as well as back-to-back street drives, we have a general idea of how the new suspension is going to stack up. Even though we didn't have time to go over the car with a plumb bob, angle finders and precision measuring devices, the educated eyeball can impart a good amount of information in a short time.

Rear Suspension
Due to their ability to keep tires on the tarmac for more grip under cornering roll, multi-link designs are usually coveted by enthusiasts over more mundane sedan suspension systems, like the economical and pedestrian MacPherson strut. Initially, we were puzzled why Subaru put a multi-link in the back of the Impreza at all. Nose-heavy, understeer-prone all-wheel-drive cars are usually hurting for front grip. Putting a multi-link in the back seems a little counterproductive for performance, as it tends to increase dork-safe-but-racer-annoying understeer.

Our take is this: Subaru did it to offer a car with a wider, flatter trunk or rear hatch area, since the shocks no longer reach all the way up into the rear shelf sheetmetal. With no intrusion of MacPherson struts into the shock towers, the trunk (or rear cargo area) can be one vast plain of flatness, better to store luggage, race tires or bodies. Doing away with shock towers also means that the rear seats can be pushed closer to the wheel wells. There are perhaps some safety reasons too, as it is possible to design more crush space from side and rear impacts with a multi-link set-up. Or maybe it's as simple as Subaru trying to emulate its archrival-the new Mitsubishi Lancer/Evo X, which (obviously) has Mac struts in the front and a multi-link in the rear.

The Impreza's multi-link suspension has its geometry arranged for greater negative camber gain under roll compared to the old car's MacPherson struts. This keeps the tire tread flat to the ground, rather than allowing it to tilt up onto its outside edge, thereby reducing the contact patch. With this footprint maintained, grip is improved during cornering when compared to the old strut set-up.

Some multi-link set-ups, like the one found in the back of the Scion tC, have little negative camber gain, but this suspension has a good amount. With shorter front lower links, the new Impreza suspension will also toe-in the rear wheels passively under roll. Both measures tend to increase rear traction and thus understeer, since the front remains the same and provides stability when cornering. And that's what the 2008 Impreza feels like on the road. One of the things in the old STI that made cornering interesting was its penchant for corner-exit power-on oversteer. Perhaps these changes will subdue that tendency, although they will probably affect mid-turn rotation as well, something experienced drivers may find annoying on the track.

We also noted, through inspection of the control arm mounting angles, that the new Impreza's rear suspension has more anti-squat geometry than the old set-up. This will reduce the amount of annoying torque-induced squat under acceleration, familiar to anyone who has drag-launched an STI with a street suspension. This also means the suspension will become more bound up under torque load, increasing resistance to movement.

More anti-squat can mean a greater tendency toward oversteer when on the gas, because the bind will act like an increase in suspension stiffness when the throttle is applied. Hopefully, this may cancel out some of the understeer-inducing effects of greater negative camber gain and passive toe-in; not too noticeable in our putt-putt base Impreza, but we reckon it will be a large factor in the chassis dynamics of the more-powerful upcoming STI.

Subaru has used small rubber bushings at the pivot points. This is good, because it reduces overall compliance and, under load, helps keep tires pointed where Subaru's engineers intended. We've become rather dismayed at the huge, squishy rubber bon-bons many late-model suspension systems are sprouting in an attempt to reduce noise, vibration and harshness. We also noticed that although our basic non-turbo test car has rear drum brakes (unlike the previous generation), bosses for brake discs and calipers are on its uprights. Likewise, holes and braces are present to allow subsequent addition of anti-roll bars. However, please note that this is a pre-production car and these useful appendages may disappear from showroom vehicles. Ironically, our 2007 base Impreza had a small rear bar.

Front Suspension
The front suspension on the previous-generation Impreza and WRX had some unpopular traits. Its steering was plagued with a numb on-center feel and a poor return to center when cornering. High-power modified WRX models have a hint of torque steer and a large amount of anti-dive/lift geometry. This leads to a non-linear build-up of understeer when trail braking and when on the throttle at corner exit. Compared to the turn-in of its rival, the Lancer Evolution, the WRX felt considerably less sharp.

Subaru's engineers have been working on these issues. At a glance, the front suspension appears to be identical to the old car (the tried-and-true MacPherson strut design), but there have been many subtle changes in front-end geometry-the most notable being more positive caster and a greater steering axis inclination angle.

Both changes increase straight-line stability, on-center feel and steering return to center. Increasing positive caster also improves turn-in and contributes to negative camber gain as the steering wheel is turned off-center. In addition to improving on-center feel and straight-line stability, increasing the steering axis inclination angle moves The Dave Point closer to the center of the front tires' contact patch, reducing the tendency for torque steer and steering pull when accelerating or braking over two surfaces with different levels of traction.

The most amusing thing is that all the changes Subaru has adopted are already popular modifications performed by top tuners on the current Impreza. We wish the new multi-link rear suspension had found its way to the front, but realistically, any multi-link would be difficult to package, due to the width of the boxer engine.

It also appears that the new car has less anti-lift and anti-dive incorporated into the front suspension geometry, as the front lower control arm is more parallel to the ground than the older car. This change is well known in the aftermarket, featured in many popular anti-lift kits that relocate the rear pivot of the lower control arm, reducing anti-dive and increasing positive caster at the same time.

Driving Impressions
Due to our limited time with the new car, our driving impressions were confined to a short street drive-not the place to conduct handling evaluations. So we had to be content with some mild seven-tenths driving to get more of a general feel of the differences. As we expected, the new car has greatly improved steering feel. The center is less numb, with more definition and the steering wheel centers itself crisply when recovering from a turn. There is not a hint of torque steer, but, with a naturally aspirated motor, there isn't as much torque to induce any. Turn-in response is more immediate-nervous almost, on such soft suspension and hard tires. But so far, a general thumbs-up.

On the throttle, the new car exhibits very little squat. This was the complete opposite in the previous-generation Impreza, as that car had less dive under braking and more rear squat under acceleration. Although neither base car have anywhere close to enough power to break the rear tires loose, the new one feels more connected and solid in all attributes, except for an annoying tendency to dive under braking. On a non-suspension-related note, the new car also has an improved braking feel with a harder, higher pedal and better modulation. But the older Impreza, with a slightly stiffer suspension, still feels like more like a driver's machine compared to the new Impreza's high-precision, but soft econobox feel.

These suspension changes are a good step forward for overall performance and safer driveability for the masses. The aftermarket can easily address brake dive with stiffer springs and improved dampers. Changes to the front-end geometry basically mimic what top suspension tuners are already doing to the old car, making for a much better base platform from which to build. In the rear, we can expect the new suspension to improve traction and the aftermarket will quickly find interesting ways to optimize it for performance driving and motorsport.

We can't wait for the upcoming STI to see what the changes feel like with some real power behind them. A new project WRX or STI might even be in the works for us some time soon. If that's the case, then we'll really wring the all-new Impreza by the neck and give you a blow-by-blow account of what works and what doesn't.

Photo Gallery: 2008 Subaru Impreza Suspension - Sport Compact Car Magazine

Read More |
Digg It |
Add to del.icio.us

Project Ford Focus SVT

Project Ford Focus SVT

Former Associate Senior Editor Jared Holstein can dance like you can't believe. He can drive a car right to the edge of disaster while turning amazingly fast lap times. He's also cultured, with enough knowledge of fashion, art, music, fine food and drink to make the Queer Eye guys run for their contracts. The only problem is, he has zero mechanical sympathy and a definite knack for turning all things mechanical into a scrap heap at the drop of a hat.

Before he left SCC to expand his journalistic horizons, Holstein took our turbocharged Project Ford Focus SVT out for a spin and, as a going away present to us, did quite a number on the Zetec engine's bottom end. Because Holstein is Holstein, we forgave him for the ton of rebuilding work, as this was not an intentional act, but rather something as natural to him as, well, breaking stuff.

We learned a harsh lesson in automotive reality about the combination of a 10.2:1 compression ratio, cast pistons, a turbocharger, crappy 91-octane California gas and an on-the-fritz MAF being right on the edge. Throw in a driver with a lead foot and an apparently deaf ear towards the sound of detonation, and you get one very dead motor.A postmortem examination found completely nuked pistons. The ring lands were more than just fractured or pinched (the normal sure-fire signs of detonation damage), they were completely gone. The rings were not just stuck and scored but melted, with large spans missing. Even the skirts were melted. And it wasn't just the pistons. The block was scored so badly that it couldn't be saved, even by an enthusiastic overbore.

We had never witnessed such destruction before. Although we were left with a big repair task, we made a commitment to bring Project Focus SVT back, so that, one day, it might finally face off with a Mustang Cobra on the track. FocusSport, one of the leading tuners of the Focus platform, generously stepped forward to help us put our dead player back together.

The factory Ford Zetec engine is a high performance powerplant with a strong bottom end and a tough cast iron block. The Focus SVT version has beefed-up pistons, crank and rods. The stock internal components are usually reliable until about 280 to 300bhp. Untouched, the engine makes a respectable 170bhp with a 10.2:1 compression ratio-not a forced induction-friendly number. Not that that matters, since those pistons are now just paperweights. To give us a more forgiving margin, considering our home state's penchant for having some of the worst fuel in the nation, we decided to reduce the compression ratio to a more turbo-friendly 9:1, courtesy of some forged pistons from JE Pistons.In order to avoid terminal engine issues, we were compelled to obtain some of the toughest possible pistons. Most forged pistons are manufactured from either 2618 or 4032 aluminum alloy. Both have advantages and disadvantages, depending on application. Racing engines usually require stronger low-silicon 2618 alloy, while less demanding applications favor the greater silicon content found in 4032 alloy.

Our pistons started as blanks, forged from 2618 alloy. This alloy is extremely ductile and strong, perfect for the stress and pounding of a forced induction set-up, or dealing with Holstein. The primary disadvantage is a greater coefficient of thermal expansion. When exposed to heat, a piston made of 2618 alloy will expand approximately 13 percent more than its 4032 counterpart. To accommodate the additional expansion, more initial piston-to-wall clearance is necessary. Extra clearance results in more piston noise at cold start-up, but this effect diminishes as operating temperatures are reached.

JE Pistons' extensive engineering experience and tight manufacturing tolerances result in a precisely shaped piston skirt profile. A typical skirt profile will incorporate a 'barrel shape' (when looking at the piston side-on), with more clearance at the heat-soaked top of the piston, less mid-skirt, and an inward taper at the base. This design optimizes clearance across the skirt face, based on the location of heat. JE pistons feature some of the tightest bore clearance specifications of any low-silicon piston. The correct amount of clearance will reduce 'slap' against the cylinder walls for less wear and quieter operation. The pistons are also optimized for strength and lightness-ours weigh just 299 grams each.

We used shelf part number 185915. These pistons feature many of JE's technically advanced designs, such as double forced pin oilers, contact reduction and accumulator grooves. Contact reduction grooves are small waves machined into the contact face of the top ring land. They serve as a labyrinth baffle to help buffer shock waves caused by detonation, minimizing ring flutter and damage. This design also gives the aluminum room to expand and prevents scuffing against the cylinder wall.

The accumulator groove is possibly the most beneficial feature. This V-style groove is located on the second ring land between the top and second rings. It acts like a reservoir for high-pressure combustion gases that leak past the first ring, reducing the pressure that can lift the top ring from the base of the groove and cause it to lose its seal. This difference is most significant at high revs.

Double forced pin oilers feed the wrist pin with a steady supply of oil pumped in from the oil ring groove. Proper wrist pin lubrication is crucial, especially in engines using forced induction. The pistons also use a thick-walled, straight-diameter, high-carbon steel piston pin, a better choice to reduce flex in high-load, forced induction applications. The pin is held in place with Spiro-Locks, probably the most secure pin anchoring system available.

The top ring land is made thicker, to increase land strength and move the top ring away from the intense environment of the combustion chamber. This is the opposite strategy of the damage-prone OEM piston that features a short top ring land to reduce hydrocarbon emissions. The tops of our pistons use a 6.9cc dish to reduce compression ratio. The dish design puts flat areas of the piston top in line with the quench pads in the cylinder head. This causes turbulence in the mixture as the piston reaches top dead center, resulting in complete burn and a reduced likelihood of detonation. This type of piston top configuration is called a reverse deflector.

JE Pro Seal rings were also selected. They're significantly thinner than the OEM ring set. This design results in less radial tension, therefore less friction and more power. The thinner profile also means that the rings are lighter and less prone to inertial flutter from the base of the ring groove. Plus, they won't lose their seal at high revs. The chrome-faced top and oil rings are perfect for our iron bores.

JE makes the 185915 pistons for 85mm bore sizes. This is approximately 0.007-inch larger than the standard Zetec bore. The design incorporates a piston-to-wall clearance of 0.004-inch. Honing our bores 0.007-inch oversize to exactly 85mm is all that is necessary to prepare them properly. We handed our block to Cosworth Engineering in Torrance, California, to make use of its world-class machining facility.

To hang the pistons, we needed to find a stronger connecting rod. We chose Eagle for its ESP rods, forged from a high nickel and chromium 4340 steel alloy. The nickel and chromium give the steel a high tensile strength and a much improved fatigue resistance over regular high carbon, and even chromoly steels. A good feature is that the rod is forged in two pieces, with the cap forged separately. This allows it to have the metal's grain flow in a circle around the big end bore. With this forging method, there is greater strength and less distortion of the rod's big end under load. Typically, rods are machined from a one-piece forging, where the grain flow is along the length of the rod. When the big end of the rod is machined, the grain is interrupted by the hole.

The rod's beams are machined in an H profile. This profile is stiffer, putting more material where it is needed for strength and none elsewhere. With this sort of construction, an Eagle rod is typically about 100 grams lighter that most stock rods. In the machined valley of the H is a small rib at the base. This enhances the beam's strength.

Piston pin oiling holes are drilled upwards at an angle towards the pin. This is unlike the standard practice, where pin oiling comes from a single hole drilled at the top of the rod. This hole significantly weakens the small end of the rod. By putting two smaller holes at the bottom, at the less stressed portion of the pin boss, Eagle has a much stronger part.

The rod's entire surface is machine finished. This ensures consistency in both dimension and weight. After machining, the rod is subjected to shotpeening, a process where it is bombarded by hard steel shot at high velocities.

Shotpeening helps refine the metal's grain over the surface of the rod, creating a finely grained compressed layer of steel where cracks have a hard time propagating. Shotpeening improves fatigue resistance in most steel parts by over 100 percent.

The piston pin bushing is tough silicon bronze, one of the most wear-resistant bushing materials available. As the rod bolts are the most critical part on the connecting rod, no expense was spared. Eagle uses genuine ARP 8740 7/16-inch rod bolts for all its sport compact series. These have a tensile strength of over 230,000psi, many times stronger than the factory bolts. Altogether, each new piston, pin and rod assembly weighs 1.9 pounds. The far weaker stock components weigh 2.35 pounds.

Once the block machining was complete and the parts lined up, FocusSport assembled our motor's bottom end, making doubly sure it would hold up if Holstein ever found his way behind the wheel of Project Focus SVT again. All critical clearances were double-checked and the bearings replaced with genuine Ford parts. As the stock SVT crankshaft is a beefy fully counterweighted forged part, FocusSport retained it.

With our bulletproof bottom end cinched up, next time we'll be ready to bolt on our Cosworth cylinder head, Quaife-equipped transmission and stuff it all back into the chassis. That is, just as soon as we kill all the black widow spiders that have claimed our Focus as their home for the past two years.

Photo Gallery: Project Ford Focus SVT Pt 6 - Sport Compact Car Magazine

Read More |
Digg It |
Add to del.icio.us

Project Ford Focus SVT

Project Ford Focus SVT

Former Associate Senior Editor Jared Holstein can dance like you can't believe. He can drive a car right to the edge of disaster while turning amazingly fast lap times. He's also cultured, with enough knowledge of fashion, art, music, fine food and drink to make the Queer Eye guys run for their contracts. The only problem is, he has zero mechanical sympathy and a definite knack for turning all things mechanical into a scrap heap at the drop of a hat.

Before he left SCC to expand his journalistic horizons, Holstein took our turbocharged Project Ford Focus SVT out for a spin and, as a going away present to us, did quite a number on the Zetec engine's bottom end. Because Holstein is Holstein, we forgave him for the ton of rebuilding work, as this was not an intentional act, but rather something as natural to him as, well, breaking stuff.

We learned a harsh lesson in automotive reality about the combination of a 10.2:1 compression ratio, cast pistons, a turbocharger, crappy 91-octane California gas and an on-the-fritz MAF being right on the edge. Throw in a driver with a lead foot and an apparently deaf ear towards the sound of detonation, and you get one very dead motor.A postmortem examination found completely nuked pistons. The ring lands were more than just fractured or pinched (the normal sure-fire signs of detonation damage), they were completely gone. The rings were not just stuck and scored but melted, with large spans missing. Even the skirts were melted. And it wasn't just the pistons. The block was scored so badly that it couldn't be saved, even by an enthusiastic overbore.

We had never witnessed such destruction before. Although we were left with a big repair task, we made a commitment to bring Project Focus SVT back, so that, one day, it might finally face off with a Mustang Cobra on the track. FocusSport, one of the leading tuners of the Focus platform, generously stepped forward to help us put our dead player back together.

The factory Ford Zetec engine is a high performance powerplant with a strong bottom end and a tough cast iron block. The Focus SVT version has beefed-up pistons, crank and rods. The stock internal components are usually reliable until about 280 to 300bhp. Untouched, the engine makes a respectable 170bhp with a 10.2:1 compression ratio-not a forced induction-friendly number. Not that that matters, since those pistons are now just paperweights. To give us a more forgiving margin, considering our home state's penchant for having some of the worst fuel in the nation, we decided to reduce the compression ratio to a more turbo-friendly 9:1, courtesy of some forged pistons from JE Pistons.In order to avoid terminal engine issues, we were compelled to obtain some of the toughest possible pistons. Most forged pistons are manufactured from either 2618 or 4032 aluminum alloy. Both have advantages and disadvantages, depending on application. Racing engines usually require stronger low-silicon 2618 alloy, while less demanding applications favor the greater silicon content found in 4032 alloy.

Our pistons started as blanks, forged from 2618 alloy. This alloy is extremely ductile and strong, perfect for the stress and pounding of a forced induction set-up, or dealing with Holstein. The primary disadvantage is a greater coefficient of thermal expansion. When exposed to heat, a piston made of 2618 alloy will expand approximately 13 percent more than its 4032 counterpart. To accommodate the additional expansion, more initial piston-to-wall clearance is necessary. Extra clearance results in more piston noise at cold start-up, but this effect diminishes as operating temperatures are reached.

JE Pistons' extensive engineering experience and tight manufacturing tolerances result in a precisely shaped piston skirt profile. A typical skirt profile will incorporate a 'barrel shape' (when looking at the piston side-on), with more clearance at the heat-soaked top of the piston, less mid-skirt, and an inward taper at the base. This design optimizes clearance across the skirt face, based on the location of heat. JE pistons feature some of the tightest bore clearance specifications of any low-silicon piston. The correct amount of clearance will reduce 'slap' against the cylinder walls for less wear and quieter operation. The pistons are also optimized for strength and lightness-ours weigh just 299 grams each.

We used shelf part number 185915. These pistons feature many of JE's technically advanced designs, such as double forced pin oilers, contact reduction and accumulator grooves. Contact reduction grooves are small waves machined into the contact face of the top ring land. They serve as a labyrinth baffle to help buffer shock waves caused by detonation, minimizing ring flutter and damage. This design also gives the aluminum room to expand and prevents scuffing against the cylinder wall.

The accumulator groove is possibly the most beneficial feature. This V-style groove is located on the second ring land between the top and second rings. It acts like a reservoir for high-pressure combustion gases that leak past the first ring, reducing the pressure that can lift the top ring from the base of the groove and cause it to lose its seal. This difference is most significant at high revs.

Double forced pin oilers feed the wrist pin with a steady supply of oil pumped in from the oil ring groove. Proper wrist pin lubrication is crucial, especially in engines using forced induction. The pistons also use a thick-walled, straight-diameter, high-carbon steel piston pin, a better choice to reduce flex in high-load, forced induction applications. The pin is held in place with Spiro-Locks, probably the most secure pin anchoring system available.

The top ring land is made thicker, to increase land strength and move the top ring away from the intense environment of the combustion chamber. This is the opposite strategy of the damage-prone OEM piston that features a short top ring land to reduce hydrocarbon emissions. The tops of our pistons use a 6.9cc dish to reduce compression ratio. The dish design puts flat areas of the piston top in line with the quench pads in the cylinder head. This causes turbulence in the mixture as the piston reaches top dead center, resulting in complete burn and a reduced likelihood of detonation. This type of piston top configuration is called a reverse deflector.

JE Pro Seal rings were also selected. They're significantly thinner than the OEM ring set. This design results in less radial tension, therefore less friction and more power. The thinner profile also means that the rings are lighter and less prone to inertial flutter from the base of the ring groove. Plus, they won't lose their seal at high revs. The chrome-faced top and oil rings are perfect for our iron bores.

JE makes the 185915 pistons for 85mm bore sizes. This is approximately 0.007-inch larger than the standard Zetec bore. The design incorporates a piston-to-wall clearance of 0.004-inch. Honing our bores 0.007-inch oversize to exactly 85mm is all that is necessary to prepare them properly. We handed our block to Cosworth Engineering in Torrance, California, to make use of its world-class machining facility.

To hang the pistons, we needed to find a stronger connecting rod. We chose Eagle for its ESP rods, forged from a high nickel and chromium 4340 steel alloy. The nickel and chromium give the steel a high tensile strength and a much improved fatigue resistance over regular high carbon, and even chromoly steels. A good feature is that the rod is forged in two pieces, with the cap forged separately. This allows it to have the metal's grain flow in a circle around the big end bore. With this forging method, there is greater strength and less distortion of the rod's big end under load. Typically, rods are machined from a one-piece forging, where the grain flow is along the length of the rod. When the big end of the rod is machined, the grain is interrupted by the hole.

The rod's beams are machined in an H profile. This profile is stiffer, putting more material where it is needed for strength and none elsewhere. With this sort of construction, an Eagle rod is typically about 100 grams lighter that most stock rods. In the machined valley of the H is a small rib at the base. This enhances the beam's strength.

Piston pin oiling holes are drilled upwards at an angle towards the pin. This is unlike the standard practice, where pin oiling comes from a single hole drilled at the top of the rod. This hole significantly weakens the small end of the rod. By putting two smaller holes at the bottom, at the less stressed portion of the pin boss, Eagle has a much stronger part.

The rod's entire surface is machine finished. This ensures consistency in both dimension and weight. After machining, the rod is subjected to shotpeening, a process where it is bombarded by hard steel shot at high velocities.

Shotpeening helps refine the metal's grain over the surface of the rod, creating a finely grained compressed layer of steel where cracks have a hard time propagating. Shotpeening improves fatigue resistance in most steel parts by over 100 percent.

The piston pin bushing is tough silicon bronze, one of the most wear-resistant bushing materials available. As the rod bolts are the most critical part on the connecting rod, no expense was spared. Eagle uses genuine ARP 8740 7/16-inch rod bolts for all its sport compact series. These have a tensile strength of over 230,000psi, many times stronger than the factory bolts. Altogether, each new piston, pin and rod assembly weighs 1.9 pounds. The far weaker stock components weigh 2.35 pounds.

Once the block machining was complete and the parts lined up, FocusSport assembled our motor's bottom end, making doubly sure it would hold up if Holstein ever found his way behind the wheel of Project Focus SVT again. All critical clearances were double-checked and the bearings replaced with genuine Ford parts. As the stock SVT crankshaft is a beefy fully counterweighted forged part, FocusSport retained it.

With our bulletproof bottom end cinched up, next time we'll be ready to bolt on our Cosworth cylinder head, Quaife-equipped transmission and stuff it all back into the chassis. That is, just as soon as we kill all the black widow spiders that have claimed our Focus as their home for the past two years.

Photo Gallery: Project Ford Focus SVT Pt 6 - Sport Compact Car Magazine

Read More |
Digg It |
Add to del.icio.us

For Better Or Worse

For Better Or Worse

The big news regarding the 2008 Impreza was the re-designed chassis and resulting suspension changes. Until now, though, no one really knew how the sophisticated rear multi-link system would compare to the old MacPherson strut set-up of previous generations. WRX fans have been rejoicing, because multi-link can only mean better performance; on paper, a double A-arm suspension would have an advantage in terms of camber gain. But is the new suspension really all it's cracked up to be?

We were able to take a brief look at the undercarriage of a new 2008 Impreza sedan, side-by-side with a 2007 Impreza wagon. Doing some quick measurements, as well as back-to-back street drives, we have a general idea of how the new suspension is going to stack up. Even though we didn't have time to go over the car with a plumb bob, angle finders and precision measuring devices, the educated eyeball can impart a good amount of information in a short time.

Rear Suspension
Due to their ability to keep tires on the tarmac for more grip under cornering roll, multi-link designs are usually coveted by enthusiasts over more mundane sedan suspension systems, like the economical and pedestrian MacPherson strut. Initially, we were puzzled why Subaru put a multi-link in the back of the Impreza at all. Nose-heavy, understeer-prone all-wheel-drive cars are usually hurting for front grip. Putting a multi-link in the back seems a little counterproductive for performance, as it tends to increase dork-safe-but-racer-annoying understeer.

Our take is this: Subaru did it to offer a car with a wider, flatter trunk or rear hatch area, since the shocks no longer reach all the way up into the rear shelf sheetmetal. With no intrusion of MacPherson struts into the shock towers, the trunk (or rear cargo area) can be one vast plain of flatness, better to store luggage, race tires or bodies. Doing away with shock towers also means that the rear seats can be pushed closer to the wheel wells. There are perhaps some safety reasons too, as it is possible to design more crush space from side and rear impacts with a multi-link set-up. Or maybe it's as simple as Subaru trying to emulate its archrival-the new Mitsubishi Lancer/Evo X, which (obviously) has Mac struts in the front and a multi-link in the rear.

The Impreza's multi-link suspension has its geometry arranged for greater negative camber gain under roll compared to the old car's MacPherson struts. This keeps the tire tread flat to the ground, rather than allowing it to tilt up onto its outside edge, thereby reducing the contact patch. With this footprint maintained, grip is improved during cornering when compared to the old strut set-up.

Some multi-link set-ups, like the one found in the back of the Scion tC, have little negative camber gain, but this suspension has a good amount. With shorter front lower links, the new Impreza suspension will also toe-in the rear wheels passively under roll. Both measures tend to increase rear traction and thus understeer, since the front remains the same and provides stability when cornering. And that's what the 2008 Impreza feels like on the road. One of the things in the old STI that made cornering interesting was its penchant for corner-exit power-on oversteer. Perhaps these changes will subdue that tendency, although they will probably affect mid-turn rotation as well, something experienced drivers may find annoying on the track.

We also noted, through inspection of the control arm mounting angles, that the new Impreza's rear suspension has more anti-squat geometry than the old set-up. This will reduce the amount of annoying torque-induced squat under acceleration, familiar to anyone who has drag-launched an STI with a street suspension. This also means the suspension will become more bound up under torque load, increasing resistance to movement.

More anti-squat can mean a greater tendency toward oversteer when on the gas, because the bind will act like an increase in suspension stiffness when the throttle is applied. Hopefully, this may cancel out some of the understeer-inducing effects of greater negative camber gain and passive toe-in; not too noticeable in our putt-putt base Impreza, but we reckon it will be a large factor in the chassis dynamics of the more-powerful upcoming STI.

Subaru has used small rubber bushings at the pivot points. This is good, because it reduces overall compliance and, under load, helps keep tires pointed where Subaru's engineers intended. We've become rather dismayed at the huge, squishy rubber bon-bons many late-model suspension systems are sprouting in an attempt to reduce noise, vibration and harshness. We also noticed that although our basic non-turbo test car has rear drum brakes (unlike the previous generation), bosses for brake discs and calipers are on its uprights. Likewise, holes and braces are present to allow subsequent addition of anti-roll bars. However, please note that this is a pre-production car and these useful appendages may disappear from showroom vehicles. Ironically, our 2007 base Impreza had a small rear bar.

Front Suspension
The front suspension on the previous-generation Impreza and WRX had some unpopular traits. Its steering was plagued with a numb on-center feel and a poor return to center when cornering. High-power modified WRX models have a hint of torque steer and a large amount of anti-dive/lift geometry. This leads to a non-linear build-up of understeer when trail braking and when on the throttle at corner exit. Compared to the turn-in of its rival, the Lancer Evolution, the WRX felt considerably less sharp.

Subaru's engineers have been working on these issues. At a glance, the front suspension appears to be identical to the old car (the tried-and-true MacPherson strut design), but there have been many subtle changes in front-end geometry-the most notable being more positive caster and a greater steering axis inclination angle.

Both changes increase straight-line stability, on-center feel and steering return to center. Increasing positive caster also improves turn-in and contributes to negative camber gain as the steering wheel is turned off-center. In addition to improving on-center feel and straight-line stability, increasing the steering axis inclination angle moves The Dave Point closer to the center of the front tires' contact patch, reducing the tendency for torque steer and steering pull when accelerating or braking over two surfaces with different levels of traction.

The most amusing thing is that all the changes Subaru has adopted are already popular modifications performed by top tuners on the current Impreza. We wish the new multi-link rear suspension had found its way to the front, but realistically, any multi-link would be difficult to package, due to the width of the boxer engine.

It also appears that the new car has less anti-lift and anti-dive incorporated into the front suspension geometry, as the front lower control arm is more parallel to the ground than the older car. This change is well known in the aftermarket, featured in many popular anti-lift kits that relocate the rear pivot of the lower control arm, reducing anti-dive and increasing positive caster at the same time.

Driving Impressions
Due to our limited time with the new car, our driving impressions were confined to a short street drive-not the place to conduct handling evaluations. So we had to be content with some mild seven-tenths driving to get more of a general feel of the differences. As we expected, the new car has greatly improved steering feel. The center is less numb, with more definition and the steering wheel centers itself crisply when recovering from a turn. There is not a hint of torque steer, but, with a naturally aspirated motor, there isn't as much torque to induce any. Turn-in response is more immediate-nervous almost, on such soft suspension and hard tires. But so far, a general thumbs-up.

On the throttle, the new car exhibits very little squat. This was the complete opposite in the previous-generation Impreza, as that car had less dive under braking and more rear squat under acceleration. Although neither base car have anywhere close to enough power to break the rear tires loose, the new one feels more connected and solid in all attributes, except for an annoying tendency to dive under braking. On a non-suspension-related note, the new car also has an improved braking feel with a harder, higher pedal and better modulation. But the older Impreza, with a slightly stiffer suspension, still feels like more like a driver's machine compared to the new Impreza's high-precision, but soft econobox feel.

These suspension changes are a good step forward for overall performance and safer driveability for the masses. The aftermarket can easily address brake dive with stiffer springs and improved dampers. Changes to the front-end geometry basically mimic what top suspension tuners are already doing to the old car, making for a much better base platform from which to build. In the rear, we can expect the new suspension to improve traction and the aftermarket will quickly find interesting ways to optimize it for performance driving and motorsport.

We can't wait for the upcoming STI to see what the changes feel like with some real power behind them. A new project WRX or STI might even be in the works for us some time soon. If that's the case, then we'll really wring the all-new Impreza by the neck and give you a blow-by-blow account of what works and what doesn't.

Photo Gallery: 2008 Subaru Impreza Suspension - Sport Compact Car Magazine

Read More |
Digg It |
Add to del.icio.us

Project Ford Focus SVT

Project Ford Focus SVT

Former Associate Senior Editor Jared Holstein can dance like you can't believe. He can drive a car right to the edge of disaster while turning amazingly fast lap times. He's also cultured, with enough knowledge of fashion, art, music, fine food and drink to make the Queer Eye guys run for their contracts. The only problem is, he has zero mechanical sympathy and a definite knack for turning all things mechanical into a scrap heap at the drop of a hat.

Before he left SCC to expand his journalistic horizons, Holstein took our turbocharged Project Ford Focus SVT out for a spin and, as a going away present to us, did quite a number on the Zetec engine's bottom end. Because Holstein is Holstein, we forgave him for the ton of rebuilding work, as this was not an intentional act, but rather something as natural to him as, well, breaking stuff.

We learned a harsh lesson in automotive reality about the combination of a 10.2:1 compression ratio, cast pistons, a turbocharger, crappy 91-octane California gas and an on-the-fritz MAF being right on the edge. Throw in a driver with a lead foot and an apparently deaf ear towards the sound of detonation, and you get one very dead motor.A postmortem examination found completely nuked pistons. The ring lands were more than just fractured or pinched (the normal sure-fire signs of detonation damage), they were completely gone. The rings were not just stuck and scored but melted, with large spans missing. Even the skirts were melted. And it wasn't just the pistons. The block was scored so badly that it couldn't be saved, even by an enthusiastic overbore.

We had never witnessed such destruction before. Although we were left with a big repair task, we made a commitment to bring Project Focus SVT back, so that, one day, it might finally face off with a Mustang Cobra on the track. FocusSport, one of the leading tuners of the Focus platform, generously stepped forward to help us put our dead player back together.

The factory Ford Zetec engine is a high performance powerplant with a strong bottom end and a tough cast iron block. The Focus SVT version has beefed-up pistons, crank and rods. The stock internal components are usually reliable until about 280 to 300bhp. Untouched, the engine makes a respectable 170bhp with a 10.2:1 compression ratio-not a forced induction-friendly number. Not that that matters, since those pistons are now just paperweights. To give us a more forgiving margin, considering our home state's penchant for having some of the worst fuel in the nation, we decided to reduce the compression ratio to a more turbo-friendly 9:1, courtesy of some forged pistons from JE Pistons.In order to avoid terminal engine issues, we were compelled to obtain some of the toughest possible pistons. Most forged pistons are manufactured from either 2618 or 4032 aluminum alloy. Both have advantages and disadvantages, depending on application. Racing engines usually require stronger low-silicon 2618 alloy, while less demanding applications favor the greater silicon content found in 4032 alloy.

Our pistons started as blanks, forged from 2618 alloy. This alloy is extremely ductile and strong, perfect for the stress and pounding of a forced induction set-up, or dealing with Holstein. The primary disadvantage is a greater coefficient of thermal expansion. When exposed to heat, a piston made of 2618 alloy will expand approximately 13 percent more than its 4032 counterpart. To accommodate the additional expansion, more initial piston-to-wall clearance is necessary. Extra clearance results in more piston noise at cold start-up, but this effect diminishes as operating temperatures are reached.

JE Pistons' extensive engineering experience and tight manufacturing tolerances result in a precisely shaped piston skirt profile. A typical skirt profile will incorporate a 'barrel shape' (when looking at the piston side-on), with more clearance at the heat-soaked top of the piston, less mid-skirt, and an inward taper at the base. This design optimizes clearance across the skirt face, based on the location of heat. JE pistons feature some of the tightest bore clearance specifications of any low-silicon piston. The correct amount of clearance will reduce 'slap' against the cylinder walls for less wear and quieter operation. The pistons are also optimized for strength and lightness-ours weigh just 299 grams each.

We used shelf part number 185915. These pistons feature many of JE's technically advanced designs, such as double forced pin oilers, contact reduction and accumulator grooves. Contact reduction grooves are small waves machined into the contact face of the top ring land. They serve as a labyrinth baffle to help buffer shock waves caused by detonation, minimizing ring flutter and damage. This design also gives the aluminum room to expand and prevents scuffing against the cylinder wall.

The accumulator groove is possibly the most beneficial feature. This V-style groove is located on the second ring land between the top and second rings. It acts like a reservoir for high-pressure combustion gases that leak past the first ring, reducing the pressure that can lift the top ring from the base of the groove and cause it to lose its seal. This difference is most significant at high revs.

Double forced pin oilers feed the wrist pin with a steady supply of oil pumped in from the oil ring groove. Proper wrist pin lubrication is crucial, especially in engines using forced induction. The pistons also use a thick-walled, straight-diameter, high-carbon steel piston pin, a better choice to reduce flex in high-load, forced induction applications. The pin is held in place with Spiro-Locks, probably the most secure pin anchoring system available.

The top ring land is made thicker, to increase land strength and move the top ring away from the intense environment of the combustion chamber. This is the opposite strategy of the damage-prone OEM piston that features a short top ring land to reduce hydrocarbon emissions. The tops of our pistons use a 6.9cc dish to reduce compression ratio. The dish design puts flat areas of the piston top in line with the quench pads in the cylinder head. This causes turbulence in the mixture as the piston reaches top dead center, resulting in complete burn and a reduced likelihood of detonation. This type of piston top configuration is called a reverse deflector.

JE Pro Seal rings were also selected. They're significantly thinner than the OEM ring set. This design results in less radial tension, therefore less friction and more power. The thinner profile also means that the rings are lighter and less prone to inertial flutter from the base of the ring groove. Plus, they won't lose their seal at high revs. The chrome-faced top and oil rings are perfect for our iron bores.

JE makes the 185915 pistons for 85mm bore sizes. This is approximately 0.007-inch larger than the standard Zetec bore. The design incorporates a piston-to-wall clearance of 0.004-inch. Honing our bores 0.007-inch oversize to exactly 85mm is all that is necessary to prepare them properly. We handed our block to Cosworth Engineering in Torrance, California, to make use of its world-class machining facility.

To hang the pistons, we needed to find a stronger connecting rod. We chose Eagle for its ESP rods, forged from a high nickel and chromium 4340 steel alloy. The nickel and chromium give the steel a high tensile strength and a much improved fatigue resistance over regular high carbon, and even chromoly steels. A good feature is that the rod is forged in two pieces, with the cap forged separately. This allows it to have the metal's grain flow in a circle around the big end bore. With this forging method, there is greater strength and less distortion of the rod's big end under load. Typically, rods are machined from a one-piece forging, where the grain flow is along the length of the rod. When the big end of the rod is machined, the grain is interrupted by the hole.

The rod's beams are machined in an H profile. This profile is stiffer, putting more material where it is needed for strength and none elsewhere. With this sort of construction, an Eagle rod is typically about 100 grams lighter that most stock rods. In the machined valley of the H is a small rib at the base. This enhances the beam's strength.

Piston pin oiling holes are drilled upwards at an angle towards the pin. This is unlike the standard practice, where pin oiling comes from a single hole drilled at the top of the rod. This hole significantly weakens the small end of the rod. By putting two smaller holes at the bottom, at the less stressed portion of the pin boss, Eagle has a much stronger part.

The rod's entire surface is machine finished. This ensures consistency in both dimension and weight. After machining, the rod is subjected to shotpeening, a process where it is bombarded by hard steel shot at high velocities.

Shotpeening helps refine the metal's grain over the surface of the rod, creating a finely grained compressed layer of steel where cracks have a hard time propagating. Shotpeening improves fatigue resistance in most steel parts by over 100 percent.

The piston pin bushing is tough silicon bronze, one of the most wear-resistant bushing materials available. As the rod bolts are the most critical part on the connecting rod, no expense was spared. Eagle uses genuine ARP 8740 7/16-inch rod bolts for all its sport compact series. These have a tensile strength of over 230,000psi, many times stronger than the factory bolts. Altogether, each new piston, pin and rod assembly weighs 1.9 pounds. The far weaker stock components weigh 2.35 pounds.

Once the block machining was complete and the parts lined up, FocusSport assembled our motor's bottom end, making doubly sure it would hold up if Holstein ever found his way behind the wheel of Project Focus SVT again. All critical clearances were double-checked and the bearings replaced with genuine Ford parts. As the stock SVT crankshaft is a beefy fully counterweighted forged part, FocusSport retained it.

With our bulletproof bottom end cinched up, next time we'll be ready to bolt on our Cosworth cylinder head, Quaife-equipped transmission and stuff it all back into the chassis. That is, just as soon as we kill all the black widow spiders that have claimed our Focus as their home for the past two years.

Photo Gallery: Project Ford Focus SVT Pt 6 - Sport Compact Car Magazine

Read More |
Digg It |
Add to del.icio.us

For Better Or Worse

For Better Or Worse

The big news regarding the 2008 Impreza was the re-designed chassis and resulting suspension changes. Until now, though, no one really knew how the sophisticated rear multi-link system would compare to the old MacPherson strut set-up of previous generations. WRX fans have been rejoicing, because multi-link can only mean better performance; on paper, a double A-arm suspension would have an advantage in terms of camber gain. But is the new suspension really all it's cracked up to be?

We were able to take a brief look at the undercarriage of a new 2008 Impreza sedan, side-by-side with a 2007 Impreza wagon. Doing some quick measurements, as well as back-to-back street drives, we have a general idea of how the new suspension is going to stack up. Even though we didn't have time to go over the car with a plumb bob, angle finders and precision measuring devices, the educated eyeball can impart a good amount of information in a short time.

Rear Suspension
Due to their ability to keep tires on the tarmac for more grip under cornering roll, multi-link designs are usually coveted by enthusiasts over more mundane sedan suspension systems, like the economical and pedestrian MacPherson strut. Initially, we were puzzled why Subaru put a multi-link in the back of the Impreza at all. Nose-heavy, understeer-prone all-wheel-drive cars are usually hurting for front grip. Putting a multi-link in the back seems a little counterproductive for performance, as it tends to increase dork-safe-but-racer-annoying understeer.

Our take is this: Subaru did it to offer a car with a wider, flatter trunk or rear hatch area, since the shocks no longer reach all the way up into the rear shelf sheetmetal. With no intrusion of MacPherson struts into the shock towers, the trunk (or rear cargo area) can be one vast plain of flatness, better to store luggage, race tires or bodies. Doing away with shock towers also means that the rear seats can be pushed closer to the wheel wells. There are perhaps some safety reasons too, as it is possible to design more crush space from side and rear impacts with a multi-link set-up. Or maybe it's as simple as Subaru trying to emulate its archrival-the new Mitsubishi Lancer/Evo X, which (obviously) has Mac struts in the front and a multi-link in the rear.

The Impreza's multi-link suspension has its geometry arranged for greater negative camber gain under roll compared to the old car's MacPherson struts. This keeps the tire tread flat to the ground, rather than allowing it to tilt up onto its outside edge, thereby reducing the contact patch. With this footprint maintained, grip is improved during cornering when compared to the old strut set-up.

Some multi-link set-ups, like the one found in the back of the Scion tC, have little negative camber gain, but this suspension has a good amount. With shorter front lower links, the new Impreza suspension will also toe-in the rear wheels passively under roll. Both measures tend to increase rear traction and thus understeer, since the front remains the same and provides stability when cornering. And that's what the 2008 Impreza feels like on the road. One of the things in the old STI that made cornering interesting was its penchant for corner-exit power-on oversteer. Perhaps these changes will subdue that tendency, although they will probably affect mid-turn rotation as well, something experienced drivers may find annoying on the track.

We also noted, through inspection of the control arm mounting angles, that the new Impreza's rear suspension has more anti-squat geometry than the old set-up. This will reduce the amount of annoying torque-induced squat under acceleration, familiar to anyone who has drag-launched an STI with a street suspension. This also means the suspension will become more bound up under torque load, increasing resistance to movement.

More anti-squat can mean a greater tendency toward oversteer when on the gas, because the bind will act like an increase in suspension stiffness when the throttle is applied. Hopefully, this may cancel out some of the understeer-inducing effects of greater negative camber gain and passive toe-in; not too noticeable in our putt-putt base Impreza, but we reckon it will be a large factor in the chassis dynamics of the more-powerful upcoming STI.

Subaru has used small rubber bushings at the pivot points. This is good, because it reduces overall compliance and, under load, helps keep tires pointed where Subaru's engineers intended. We've become rather dismayed at the huge, squishy rubber bon-bons many late-model suspension systems are sprouting in an attempt to reduce noise, vibration and harshness. We also noticed that although our basic non-turbo test car has rear drum brakes (unlike the previous generation), bosses for brake discs and calipers are on its uprights. Likewise, holes and braces are present to allow subsequent addition of anti-roll bars. However, please note that this is a pre-production car and these useful appendages may disappear from showroom vehicles. Ironically, our 2007 base Impreza had a small rear bar.

Front Suspension
The front suspension on the previous-generation Impreza and WRX had some unpopular traits. Its steering was plagued with a numb on-center feel and a poor return to center when cornering. High-power modified WRX models have a hint of torque steer and a large amount of anti-dive/lift geometry. This leads to a non-linear build-up of understeer when trail braking and when on the throttle at corner exit. Compared to the turn-in of its rival, the Lancer Evolution, the WRX felt considerably less sharp.

Subaru's engineers have been working on these issues. At a glance, the front suspension appears to be identical to the old car (the tried-and-true MacPherson strut design), but there have been many subtle changes in front-end geometry-the most notable being more positive caster and a greater steering axis inclination angle.

Both changes increase straight-line stability, on-center feel and steering return to center. Increasing positive caster also improves turn-in and contributes to negative camber gain as the steering wheel is turned off-center. In addition to improving on-center feel and straight-line stability, increasing the steering axis inclination angle moves The Dave Point closer to the center of the front tires' contact patch, reducing the tendency for torque steer and steering pull when accelerating or braking over two surfaces with different levels of traction.

The most amusing thing is that all the changes Subaru has adopted are already popular modifications performed by top tuners on the current Impreza. We wish the new multi-link rear suspension had found its way to the front, but realistically, any multi-link would be difficult to package, due to the width of the boxer engine.

It also appears that the new car has less anti-lift and anti-dive incorporated into the front suspension geometry, as the front lower control arm is more parallel to the ground than the older car. This change is well known in the aftermarket, featured in many popular anti-lift kits that relocate the rear pivot of the lower control arm, reducing anti-dive and increasing positive caster at the same time.

Driving Impressions
Due to our limited time with the new car, our driving impressions were confined to a short street drive-not the place to conduct handling evaluations. So we had to be content with some mild seven-tenths driving to get more of a general feel of the differences. As we expected, the new car has greatly improved steering feel. The center is less numb, with more definition and the steering wheel centers itself crisply when recovering from a turn. There is not a hint of torque steer, but, with a naturally aspirated motor, there isn't as much torque to induce any. Turn-in response is more immediate-nervous almost, on such soft suspension and hard tires. But so far, a general thumbs-up.

On the throttle, the new car exhibits very little squat. This was the complete opposite in the previous-generation Impreza, as that car had less dive under braking and more rear squat under acceleration. Although neither base car have anywhere close to enough power to break the rear tires loose, the new one feels more connected and solid in all attributes, except for an annoying tendency to dive under braking. On a non-suspension-related note, the new car also has an improved braking feel with a harder, higher pedal and better modulation. But the older Impreza, with a slightly stiffer suspension, still feels like more like a driver's machine compared to the new Impreza's high-precision, but soft econobox feel.

These suspension changes are a good step forward for overall performance and safer driveability for the masses. The aftermarket can easily address brake dive with stiffer springs and improved dampers. Changes to the front-end geometry basically mimic what top suspension tuners are already doing to the old car, making for a much better base platform from which to build. In the rear, we can expect the new suspension to improve traction and the aftermarket will quickly find interesting ways to optimize it for performance driving and motorsport.

We can't wait for the upcoming STI to see what the changes feel like with some real power behind them. A new project WRX or STI might even be in the works for us some time soon. If that's the case, then we'll really wring the all-new Impreza by the neck and give you a blow-by-blow account of what works and what doesn't.

Photo Gallery: 2008 Subaru Impreza Suspension - Sport Compact Car Magazine

Read More |
Digg It |
Add to del.icio.us