In Part 1 of Project Supra, we tackled our slipping clutch with a brand-new Centerforce unit, and so far the unit is working fine. The more miles we put on this clutch, the better it seems to get. This month we see how the Supra responds to a few upgrades, but first we need to replace our worn tires, get an alignment, change the spark plugs and get a compression check.
The car's wacky alignment wore out the front tire, so we ordered a fresh set of Bridgestone S-03 tires. We opted for tires one size wider than stock in both front and rear - a 245/40-17 and 265/40-17, respectively. The size increase shouldn't upset the handling except for a little extra grip in all four corners, and it should help with straight-line grip and reduce braking distances. The techs at Big O Tires in Redlands, Calif., mounted and balanced our Bridgestone tires and properly aligned the Supra.
The factory manual for the Mk IV Supra states that a compression test should show a variance of no more than 14 psi between all cylinders. Unfortunately, cylinder 4 was down 20 psi from the rest, while the other five were within 8 psi of each other. This doesn't signal a red flag now, but we'll probably do a cylinder head rebuild in the near future.
The final step before adding horsepower was to check the spark plugs. Sure enough, the stock Denso plugs were clearly worn out. We ordered a set of Denso Iridium I-22 spark plugs from Monarch Products through its Web site. Priced at $12 each, the change in spark plugs alone made the car run remarkably smoother, especially in the higher rpm range, without any misfires.
Armed with the proper running gear to get some affordable upgrades going, it was time to get busy at the dyno.
Advanced Engine Management Systems in Gardena, Calif., helped us by making arrangements with RD Dyno to use its Dynojet 248C dynamometer. A well-known manufacturer of high-end engine products ranging from adjustable fuel pressure regulators, intake systems and cam gears to its very popular and programmable engine management systems, AEM has been a major player in the import automotive market over the last several years.
After the car was strapped down, a fourth-gear pull registered 264.2 hp at 6250 rpm with a peak torque measurement of 234 lb-ft at 5000 rpm. Although it's a notoriously conservative dyno, AEM's Jason Siebels (whose Mk IV technical know-how got us through the day smoothly) felt it was still slightly lower than expected. His first impression was that the computer had registered a knock at some point in its life and has since kept the timing and fuel maps conservative. He unplugged the two fuel injection system fuses and waited a couple of minutes before plugging them back in. "This will reset the ECU so that it doesn't pull back so much timing," said Jason.
The fuses went back in, the car was fired up and as the wheels began to accelerate the rollers, a slightly different animal awoke, registering 275.5 hp at a much earlier 5700 rpm and a whopping 262.7 lb-ft of torque at 5000 rpm. With a gain of more than 30 lb-ft of torque in various parts of the rev range simply from resetting the ECU, the owner was pissed he hadn't thought about this sooner.
One of the best bang-for-the-buck upgrades is a decent intake system. For $210, the HKS intake system consists of a filter that features HKS's Super Lip funnel and Super Honeycomb frame, which helps to create a vacuum area on the back side of the lip. HKS claims its filters have the possibility of flowing as much air as the larger filters without taking up so much room, thanks to its relatively small size. HKS has also paid special attention to the absorption performance by using a high-adhesion moisture-type polyurethane filter. In the end, you get a filter with high filtration and limited drops in pressure. The filter was installed while the car was sitting on the dyno. The install was simple and replaced the factory air box. At 283.5 hp to the wheels, the peak number went up by 7.8 hp but the area under the curve told the true story-gains from 5800 to redline were significant, including a peak gain of more than 20 hp at a flattened 6600 rpm.