Project STi Part 4 Engine Tuning & Suspension

To continue our upgrade path we once again turned to the suspension. We were planning to attend a NASA track day at Willow Springs and wanted to have a more track ready suspension - with damn near a stock ride feel. In previous segments, we had installed Whiteline's basic handling package and Group 4 coilover suspension kit. Although we were pleased with the results, we wanted to up the ante and take the car to the next level, the next level being near-racecar levels of grip and response. We also wanted to take care of a few lingering faults that the car had in the suspension department as well.

The first step was to give the car some more roll stiffness. Although the car had little body roll as is, we knew that we would get a lot more when we bolted on a set of soft R-Compound tires. The tires' additional stick loads the chassis harder. To counter this we installed a set of Whiteline's racing XRD bars. The XRD bars are two-way adjustable in the front and three-way adjustable in the rear. We believe that bar adjustability is important in a track car as it enables you to quickly adjust the car for changes from track to track or changing from high-speed events such as track days to lower-speed tighter work such as autocross.

The stout XRD bars are a whopping 27 mm in diameter and over 160 percent stiffer than the handling package's 22 mm bars. They are also an amazing 280 percent stiffer than the stock 20 mm bars. We also installed Whiteline's optional solid spherical bearing end links and heavy-duty rear mount kit. The spherical bearings have length adjustment so they can be installed without preload, which can affect handling balance from side to side. Without the cushion of bushings, they assure that any body roll will be fully against the sway bars' full torsional stiffness. This greatly improves response. To protect the bearings, Whiteline's end links have a neat feature: urethane dust boots. To prevent the stiff rear bar from tearing off the chassis, we opted for the optional heavy-duty rear mount. This is much stronger than the stock rear mount and should prevent the bar from damaging the rear suspension. We set our bars at full soft in front and the middle of the three holes in the rear.

When shifting briskly at or near wide-open throttle, we also noticed a disturbing banging noise coming from the back and underneath the car. Sometimes when accelerating out of a tight corner we got shuddering wheelhop from the rear wheels. To alleviate this we installed Whiteline's diff carrier lock and transmission mounts. The stock diff carrier and transmission mounts are soft rubber and they allow these parts to bang around quite a bit. The Whiteline parts are made of harder 70 and 80 durometer polyurethane, and stop the unwanted motion with no detectable increase in vibration or harshness. We feel that these parts can probably go a long way to prevent drivetrain breakage as the wheelhop and banging sure felt like something was going to break.

Since we were planning to so some serious track work, we also replaced our street anti-lift kit with the Whiteline's race spec kit. The main difference between the race kit and the street kit is a change in durometer in the bushing from 70 durometer to 90. We noticed a slight increase in harshness, but felt it was barely discernible. We also noticed a slight improvement in steering response.

Finally, following Whiteline's recommendation, we installed their rear crossmember lock. When Whiteline was developing the WRX, they noted that after a few miles the torque load would skew the rear diff carrier to one side, which messed up the alignment settings. The problem was worsened when using sticky tires. They determined that the diff carrier was actually shifting 2-4 mm under load throwing the alignment off. This is a considerable amount, and it made the WRX impossible to set up properly. Because of this issue, the locks are mandatory for any WRX/STi that is going to be driven seriously.

Whiteline developed a special bolt with a large shoulder that threaded into an unused set of weld nuts in the chassis. Conveniently enough, it lined up with a hole in the crossmember in such a way it's almost as if Subaru intended to have this sort of lock in place as standard equipment. The bolt solidly locates and centers the entire rear diff carrier in place. This allows for precision alignments, but doesn't allow shifting of the rear wheels' location - no matter how hard the side loads. On our car this also eliminated the last bit of nibble from the rear of the car under acceleration.

As a last step we brought project STi to Westend Alignment in Gardena, California, for a more aggressive track alignment. We set up Project STi as follows:

If you were to drive this set-up daily, it would probably have significant negative effect on front tire wear - in which case we would probably recommend zero front toe and 1.5 to 2 degrees negative front camber.

At the track we set our tire pressures to 35 psi hot, and had a go at it. We were amazed. Our car was the best handling STi we had ever driven. Steering response was razor-like with excellent turn-in. The car refused to understeer, and would simply go into a nice easily controllable four-wheel drift. Lifting the throttle or trail braking would cause the tail to step out nicely, which would help get the car to pivot and rocket out of the turns. We felt no need to fiddle with damping or sway-bar adjustment, as we had hit the nail on the head. Tire wear was excellent under track conditions. There was no chunking, and the tires wore absolutely flat and even across the tread.

Even though I have driven and fallen in love with several modified EVOs in various track events, I was surprised to find myself liking Project STi better. The car was a killer with sharp turn-in, predictable on-throttle antics and wide powerband. Even with a young inexperienced driver, the Project STi turned racecar-like lap times and beat nearly every car in NASA's advanced lapping class. Our little car was delivering near exotic performance on a budget.

In Project STi's near future we will bring you some improvements to its clutch, cooling system, brakes, chassis stiffness and, after that, maybe some more power. After this, it will be time to bring on Project EVO. Stay tuned...

Stock IC (all temps in F)Ambient test temperature 70.6 deg FTemperatures were measured at the surface of the core 0.25" away from the end tank

XS Power IC (all temps in F)Ambient test temperature 77.4 deg FTemperatures were measured at the surface of the core 0.25" away from the end tank