Toyota Supra MKIV - Project Supra: Relaunch, Part 2

Moving on, to tune knock control we filtered out engine noise by filling the fuel tank with 92-octane fuel and a couple gallons of 112-unleaded racing fuel. Then we brought all boost cells in the ignition map to 5 degrees advanced. Without turning up the boost from the minimum 13 psi from our HKS GT wastegate, we were confident we wouldn't see detonation. When we logged the runs and tried this again at 10 degrees across the board, we were relieved to see the sensors registering pretty much the same voltage for both runs.

After driving 1,500 miles on the new engine we wanted to get an idea for how the motor was faring with the SP71-GTS turbo kit, since it felt strong. For dyno testing we sent the Supra to Imagine Auto in Lenexa, Kans., a highly respected shop that specializes in turbo Porsches. The Supra was strapped to its Mustang Dyno for some shakedown passes in Third gear, and we were pleased to see just how well it responded to little advances in ignition timing.

On its first pass, at just 5 degrees of ignition, the car surpassed 400 whp at a registered 12 psi (without turning up boost we lost a psi on the dyno due to the lesser load the car sees on the road). By doubling the ignition to 10 degrees that figure jumped to 467 whp.

Prior to dyno testing we came up with an ignition map of our own during road testing, which at 12 psi starts at 15 degrees in the midrange and slowly ramps to 17 degrees on up to 8,000 rpm. It's also tuned to drop 2 degrees for each 2.5psi increase in boost. Some people have told us we can run more ignition but we chose to stay a little on the more conservative end and not press our luck, yet. Still, the dyno confirmed a satisfying 527 whp at 7,700 rpm at just 12 psi, with a fuel-rich 11.1:1 air/fuel ratio across the board. The number was still climbing to what would've been well into the 540s at 8,000 rpm, but the dyno software was told to quit registering past 7,700 rpm for that run.

It was clear that Amazon's headwork and Ferrea valvetrain, coupled with the SP71-GTS turbo, was significantly helping airflow. After all, we still have a 3-inch exhaust system, which we hope to change soon. These runs were done using inexpensive NGK R5671A-9 plugs gapped to 0.026 inch, which work beautifully.

Since we're testing in Third gear the torque wasn't high-the last run whipped up 380 lb-ft of torque at 6,500 rpm. In Fourth gear, however, previous experience on this dyno tells us that figure should be in the mid-400s at around 5,500 rpm. Not the torquiest car, but we're taking things a little slower in the beginning. We wanted to find out what that figure in Fourth gear would be but, as Murphy's Law would have it, that 526whp run also ended with a severed clutch. At redline a loud bang, followed by the car not going back into gear told us we were done for the day. The Centerforce single-disc clutch had been holding torque fine but it didn't like the higher rpm. We hope that this was the source of our transmission woes. We'll see.

If everything comes through we'll be replacing it with Fidanza's new twin-disc setup and continue testing a variety of power adders to the Supra. Next, with our new HKS 272-degree cams in there, we'll see what cam timing our engine likes by tweaking the AEM cam gears once again, followed by seeing how boost response is affected using both a manual boost controller and our AEM electronic boost control solenoid.

Author's Note: Special thanks to Thomas Sowell and Champion Toyota's continued help and support of this project, which would be nowhere without these guys.

Also, thanks to Bill Perkins from supraforums.com, who's tuned the Supra extensively over the years and was kind enough to send us one of his AEM maps to look at and get the ball rolling faster. He had no idea he was helping our project car, but was rather just nice enough to help.