Project BMW M3 Part 9: Turbo Update

Playing with various boost levels on the dyno allowed me to see what Project M3 could handle with 91 octane and high-octane race fuel. As you might remember in Part 8, 13 psi of boost is a little too much for the motor to handle with 91 octane. The car pulled back timing heavily after 5500 rpm. Since then I had evosport swap out the AA turbo exhaust housing for another AA unit with a slightly larger aspect ratio for better flow. According to Karl Hugh, this would cause the turbo to spool up a little later, but breathe much better. I decided to do a few runs at only 10 psi. I met up with our dyno-man, Dominic Conti, at the Primedia Tech Center for some more tests.

Sure enough, at 10 psi the car didn't pull back so much timing, and it continued to make power all the way through. Not only that, but it made the same power as it did with 13 psi! The only thing we lost, rightfully so, was torque. Of course, that shouldn't be a surprise. The car's torque peaks out before 5500 rpm, and 13 psi (see ec 4/02) will show a substantial difference over 10 psi before it retards at 5500 rpm, hence the torque difference. But I decided 10 psi to be a safe boost level. With California's 91 octane, 355 is about the most horsepower I'll safely get out of Project M3.

But what happens when we mix race fuel into the equation? What's a weight loss program without the proper intake? I contacted Sunoco Race Fuels in order to try out some of its high-octane fuel. The company's race fuels are known to protect competition and high-compression engines from damage caused by detonation. The advantage with running a higher-octane fuel is its ability to withstand heat and not pre-ignite, which causes detonation or pinging.

Sunoco Fuels offers GT Plus Unleaded fuel, rated at 104 octane by the Antiknock Index (R+M)/2. Research octane and motor octane are rated at 109 and 99, respectively. I acquired some from Downs Commercial Fueling Inc., in Corona, Calif. (visit Sunoco's website for your local distributor). The GT Plus fuel is unleaded, so it won't harm catalytic converters or oxygen sensors as leaded race fuel does, and it's about the highest octane unleaded fuel money can buy. Sunoco states its GT Plus 104 fuel is intended for off-road use only. The GT 100 octane fuel is street legal, however.

I ran Project M3's tank dry and filled up with a tank full of this blue stuff. The first set of runs was done at 10 psi, and to my amazement I saw what was possibly the smoothest dyno graph I've seen to date. The lines were even smoother than when the car made its baseline runs at 218 hp! And no, the "smooth effect" of the Dynojet was not being used.

Now it was time to see the real advantages of high-octane race gas--being able to withstand higher compression chamber temperatures (i.e., from more boost). At 12 psi, Sunoco's GT Plus Unleaded fuel helped the car make another very smooth pull. We saw over 16 more peak horsepower with gobs more torque.

At 13 psi, the car started to pull back timing, but not nearly as much, and especially not as abruptly as it did when running straight 91 octane (ec 4/02). The fuel's higher octane prevented what would have otherwise been an even larger amount of detonation and gave Project M3 a whopping 37-hp increase over the last run at 13 psi with 91 octane (391.9 vs. 355.7).

It was evident Sunoco's GT Plus Unleaded 104 gas enabled Project M3 to run more boost safely, and make more power. If I don't run this stuff straight, I like to use a few gallons for every tank of gas (more so than octane booster), making it over 93 octane while keeping boost at 10 psi. After all, more than 350 whp is plenty. But with 100-percent 104-octane race fuel, I feel Project M3 is safe to run up to 12 psi.

Dominic and I played around with 14 psi, and Project M3's ECU began to abruptly pull back timing after 5500 rpm--it was too much, even for this high-octane race fuel. So we naturally saw much more torque than horsepower (437 lb-ft and 402 hp). Stay tuned; I may test a cat-less exhaust used for road racing only, and see how high Project M3 will go with much higher octane on its current 3.0 motor--after all, it may soon be getting another bigger, more powerful one.

Author's note: With analog controls on the boost controller, it's next to impossible to get the absolute exact amount of boost during two different runs on two different days if the boost controller was tampered with. For this reason, the 10 psi comparison between pump gas and race fuel was used to only show the difference in smoothness between the two dyno runs, not the gain or loss in peak torque. Only the gains in horsepower at 13 psi were mentioned over the previous month, where the gains were much more pronounced due to apparent detonation with pump gas.

Downs Commercial Fueling Inc.
1296 Magnolia Ave.
Corona, CA 92879-2098
(888) 810-3835
Fax: (909) 272-3369
E-mail: alan@downsoil.com

Sunoco Performance Products
(800) RACE GAS (800-722-3427)
www.racegas.com