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Old 10-04-2002, 02:18 PM   #5
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Default Re: Race gas w/ mostly stock WRX?

Originally posted by IndyRacer
I have seen that several i-clubbers (most with serious mods) run race gas when hitting the drag strip. I am planning to take my car to the track occasionally, and am concerned about the long term effects of using leaded race gas. I am fortunate enough to have 2 gas stations within 5 miles of my house where I can get Cam2 110 octane race gas straight from the pump. (Gotta love living in the middle of a racing community .) My car is mostly stock, but I was thinking that if I were to mix the race gas about 50:50 with premium unleaded, this would give me a nice safety margin for cranking up the boost a bit with my MBC. My question is, have any of you who use leaded race gas had a problem with O2 sensors or cats? Do you run straight race gas, or a mix? Any info would be appreciated.

If you run leaded race fuel with your factory cats you can kiss them good bye. The lead will coat the cats and they will not fire off. This results in a check engine light. Front AF sensors and o2 sensors seem to last with the ocational use of leaded fuels but life will be reduced.

All major race fuel companies make unleaded race fuel for this reason. Vp has 103 motorsport that works great with EFI cars with cats. Sunoco has several unleaded grades including a 109 octane unleaded. I have used the 109 with great results. It contains aromatics so beware, it will smell and it will turn the tail pipe white. Most of the time my car lives on 101 octane Trick unleaded as it is available at the pump a few miles from the house.

A mildly modified car such as yours will benifit from the use any of the above unleaded race fuels. On my car for example, If I run 91 octane mobil I cant safely run over 14 psi of boost without knock. Running on straight 101 trick unleaded I can run 18 knock free. One thing to note: If you are running 14 psi knock free on 91 octane fuel and then add in 101 octane fuel you will not gain power. You will be waisting your money unless you end up with more advance and or more boost. The addition of the fuel will not produce power in and of itself. All of the fuels I mentioned will increase your AF around half a point on the rich side because they burn slower. You may actualy make less power. For this reason I recomend running a mixture of 91 and race fuel.

In the end of the extreme performance range nothing beats leaded race fuel. As some other Iclubbers can attest, C16 (117 octane leaded race fuel) just about curbs detonation even at extreme boost levels. I have used C16 in the past but my car is cat free and is not a daily driven car. As I mentioned before, Race fuel burns slower and C16 is like an old Turtle. AF's typicaly richen up a full point with C16. To extract power timming will need to be advanced a great deal and mixtures will need to be leaned out.

As we all know boost increases compression ratio. Keep this in mind when choosing a race fuel. Compute your end compression ratio at your boost level target. Choose a fuel accordingly. If you cant adjust your advance and boost choose a fuel or a mixture that will not burn slow.


91 octane- Rich mixtres of 10.-1 to 10.5 to 1 for safety. 14psi max- more boost with reduced advance. When I have to pull more then 4 degrees to run a psi more I back off and run less boost.

101 trick- Cam- 11.5 to 1 AFs are safe. An extra 6 degrees of advance over 91 octane and or boost levels of 17-18 run knock free. Will richen up AF's so you need to lean out a step to make peak power.

103 VP- Designed for EFI turbocharged cars. Burns fast (like) pump fuel. Needs a pretty rich mixture to be safe. typicaly does not richen up mixture. Perfect for people with stock ECU's and more boost.

109 Sunoco. The serious "unleaded" race fuel. Uses ash and aromatics. Burns slow. AF's of 11.5 to 1 -12.0 on boost are safe. Can often times advance 10 full degrees without knock. Boost levels of 20 psi are not uncommon. Turns tail pipe white, Smells like Candy. Run this on a stock ECU car and you will probably loose power due to the slow burn effect.

C16 leaded. Burns Real slow like Kerosene. Must be mapped for this fuel to make more power. Adding to a pump fuel mapped car will net lower power. Sky is the limit on boost with this stuff. Can be used as a buffer.. Half a gallon to some 101 trick is a nice added safety margin. Kills cats and takes life away from sensors. C16 is just not needed unless you are out to break a record and are going to run insane boost and or nitrous at the same time.


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