To recap, Project Supra has undergone major surgery at Speed Force Racing. The 2JZ-GTE long block was completed using several high-end components, machine work, cryo treatment and thermal barrier coatings as covered in our April and May, 2005 issues. Finally, the time has come to talk about our turbo, fuel system and some preliminary dyno testing.
Sound Performance of Bloomingdale, Ill., is home to some of the most powerful Supras in the world. Larry Prebis and Gary Grossman head this well-known Supra tuning facility. SP sells a variety of custom-sized single-turbo upgrades for Supra owners seeking power levels anywhere from 500 to 1,500 whp. SP turbo kits include an SP-spec turbocharger, 321 stainless steel ceramic-coated header, 3-inch ceramic-coated midpipe and downpipe with wastegate recirculation and flex section, HKS GT 60mm wastegate, a 4-inch intake pipe and air filter, and oil feed and return lines with the necessary fittings. SP will soon have 4-inch midpipes and downpipes available for really high-horsepower setups.
Choosing the right turbo for this car was extremely important. Our goal is to achieve a safe 500 whp on pump gas and 750 whp on high-octane juice. At the same time we need a reasonable spool response for street use or on a road course. SP recommended the SP71-GTQ turbo upgrade to meet our needs. The SP71's compressor wheel is the only one in SP's lineup machined from billet aluminum. When asked why, SP's Larry Prebis responded, "In this specific case, we found that an extreme pressure ratio wheel intended for use in high-altitude applications just happened to work nicely with the Supra's particular engine design."
Since a billet wheel is much stronger than cast, the blades can be razor thin. This creates a turbo whine unlike anything else we've ever heard. It's awesome. Additionally, it's also lighter than a cast wheel, promoting quicker spool up.
Of course, with around a 500-whp limit, the stock fuel system had to be upgraded. Dual Walbro 255 lph high-pressure fuel pumps were ordered from Extremepsi.com, a company with a huge assortment of import performance parts at very reasonable prices. To get the pumps to work in-line, a "Y" connection needed to be fabricated. Tim Richards of Speed Force Racing welded a -8 fitting to the pump housing which allows the two pumps to dump into a single stainless steel feed line.
The -8 line was routed along the stock system's path, eventually coming to the Aeromotive 2,000 lb/hr in-line filter, which SFR plumbed into the fuel line as well. The Aeromotive fuel filter features a reusable stainless steel micron filter element, making costly fuel filter replacements a thing of the past.
From the fuel filter, the feed line continues and ends at the beautiful billet anodized HKS fuel rail. At the end of the line, the fuel empties into the combustion chambers via HKS 1000cc injectors. Granted, for this particular turbo upgrade anything above 720cc would have been sufficient but we wanted to have a fuel system that was also capable of supplying enough fuel for an even larger turbo-should we decide to test one. If you're planning to feed the fuel rail from one side, as we did, it's a good idea to feed the rail from the front-most port so the flow doesn't fight against acceleration forces.
From the back of our fuel rail we ran a -6 line to an AEM billet fuel pressure regulator. An Auto Meter 1.5-inch fuel pressure gauge was plumbed to an outlet port on the regulator so we could keep an eye on things. From the regulator, SFR routed a return line back to the fuel tank.
Jiffy-tite quick-disconnect fittings were used for their quality and ease of use, saving time (and scratches on our anodized fittings) during future fuel filter cleanings and any work on the car requiring the temporary removal of any fuel lines. The fittings are fantastic and so far have been totally leak-proof. The only drawback is the quick-disconnect mechanism makes them substantially longer, which may cause problems in tight spaces. The only place we weren't able to use a Jiffy-tite fitting was at the back of the fuel rail due to the clearance with the firewall. For that port we used an A/N fitting instead.
At long last, SFR fired the engine up with a detergent, petroleum-based oil in the crankcase. For 1,000 miles we drove the Supra around somewhat easily. After the break-in period we met with AEM's Jason Siebels and evosport's Gary Karamikian at Primedia's technical facility, where we house our Dynojet 248C.
With Jason overseeing the day's events, Gary fine-tuned the fuel curves and ignition maps for safe driving under boost using 91-octane fuel.
Our initial pulls were made in third gear running a 0.9 bar (13.2 psi) wastegate spring. At just 13 degrees ignition timing, a mid-11 air/fuel ratio and the AEM cam gears set to "0" we knew we wouldn't see big numbers right off the bat. But this was a starting point and a baseline we could use to do a quick retest of the AEM cam gears. Still, the car posted a respectable 390 whp at 6200 rpm and 347.7 lb-ft of torque at 5500 rpm.
Following Siebel's advice, the intake cam was retarded 2 degrees and the exhaust cam advanced 3 degrees before the next pass. Sadly, peak power only rose to 392 whp because, as it turned out, there wasn't much of a gain from 5900 to 6200 rpm. However, there was a significant increase of 10 to 16 lb-ft of torque from 3000 to 5300 rpm. At the top end, the torque curve flattened out from 5000 to 6000 rpm, leading to horsepower gains of 7 to 11 whp from 6400 to 6900 rpm. Once again, AEM cam gears prove they are worth every penny.
Using the AEM EMS, ignition was increased to 16 degrees-still very 91-octane friendly. The power jumped to over 406 whp, again on a third gear pull. Finally, the nut on the SP-supplied HKS wastegate was tightened to allow 1.0 bar (14.7 psi) boost. Tested in fourth gear for a better load on the turbo, the horsepower grew to over 420 whp. Not a bad start for what is now the Supra's minimum, safe horsepower using stock cams and 91 pump gas. All dyno testing was performed using petroleum-based engine oil to promote ring seat and NGK 6097 spark plugs gapped to .028 inch. We plan to switch to Mobil1 oil at about 2,500 miles.
So far the SP71 turbo has shown itself to be very street-friendly. With a large Q-trim turbine wheel inside a .81 T4 housing, the peak torque at 5000 rpm as well as the available 300+ lb-ft from 4200 rpm-on suggests we could go to a slightly larger exhaust housing should we desire to increase the power by further reducing back pressure. Given that the turbo uses an anti-surge compressor cover and no ball bearings, the spool-up is fantastic. At least for now, testing will continue on the supplied .81 turbine housing.
Now that we've got a low-boost baseline and have made sure the engine is in order, we are going to put a few more miles on it. In the meantime, we'll work on getting a boost controller installed to really get that turbo spinning and continue to put some more miles on Project Supra's newly-reborn engine. So far things seem to be going in the right direction.
However, from looking at the dyno chart, it looks like our horsepower should be nearer the 450-whp mark at 7000 rpm at our current timing and boost levels. After noticing no change with the addition of some race fuel, our power drop after 6200 rpm shows that a set of wilder cams may be in order-and we've already got HKS lined up for that. Stay tuned.