KANSAS997

So prior to my 997, I was a high reving 4 cylinder junkie... E30 M3, Type R Integra, Evo 8... you get the drift, anyway whenever I would go to the track for the weekend I would often give the babies a treat with a little 100 Oct. for the weekend. I would notice on the BMW that the plugs would have to be changed sooner than normal but that was it. My question is I have the GIAC ecu upgrade (normal pump gas mode is all that is available right now for the 3.6) Does anyone see a long term problem with running 100 octane either alone, or as a half and half mix with 91 premium... Am I going to hurt the car long term?? Also is anyone found the "ultimate tire pressure" for 20" wheel sizes, be it street or track? I ran 32 frnt and 36 rear at Heartland Park a few weeks ago on 20" wheels and it seemed to be close????

PAULSPEED

Hi,

When i ran racing gas in my lay-down Kart, the piston was always
clean. With regular gas the piston top was black. The races lasted
for one hour so that little two cycle motor got a work out. I would
say that racing gas will make your car run cleaner. I do not feel
that racing gas will make your car any faster. Racing gas will
also make your piston rings clean.

Paul

H20NOO

100 octane UNLEADED pump gas (like that sold at Unocal) will not harm your car at all. 100 octane racing fuels may not be suitable for your car or could cause problems with the catalytic converters and/or engine management and 02 sniffers especially if they have additives like tetraethyl lead. 100 octane unleaded AV-Gas is a no-no due to it's different combustion qualities and also contains dyes that may be harmful.

Bottom line - These cars have very sophisticated engine management systems that control harmful pre-ignition (aka detonation) on a cylinder by cylinder basis thousands of times a second. If you are running 93 octane pump unleaded, you won't likely get any performance boost from 100 octane without a remap of the ECU to allow for more aggressive timing. In fact, once you've reached the point of optimized combustion (about 93 octane) higher octane can actually reduce horsepower because octane slows and controls flame travel. On the other hand, these engines will run fine all day long on 91 octane (aka California crapoline) but are probably not making max power because the ignition timing is retarded to prevent detonation. Blending a couple gallons of 100 octane pump unleaded to 91 octane will probably make a difference although you may not notice it.

I experimented with this at our last track day and when I blended 100 octane with 91 octane to produce 94-95 octane, I consistently pulled 3 mph faster (127 vs 124) at the end of the front straight. Didn't feel any faster and since it was at the end of the day and more than 200 track miles, my drive onto the front straight was probably a bit more optimized as well.

There's a whole lot of science around it but rest-assured Porsche has tuned these engines for optimal power on 93 octane. If you can get it there, don't bother pushing it any higher.

MC

nkhalidi

OEM 19 recommended cold pressures are 37/44; I've found that my car likes 35/35 hot, but that's on PSCs.

For your use, I'd recommend starting at 35/35 cold and seeing how the car behaves after 3-4 laps. Come in the hot pits, adjust accordingly, and go back out. Pyrometer helps as well. Your 20s probably need more pressure than 19s because of the tiny sidewalls.

lowside67

If you're serious about the track, 20" wheels are going to really suck - tires are going to be virtually nonexistant and the wheels are heavier and hard to bend!