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What octane to run

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2002 C4S coupe manual (only mod on engine is PSE)

I know in the manual it says to run a minimum of 93 octane gasoline. Here in the western US most premium is only 91 octane. I have a place that is going to be putting in a pump site with 100 octane unleaded race fuel legal for the street. My question is should I blend the 91 with the 100 to make 93 or would I be just better off using the 100 octane straight. If your car is not built with the compression to take full advantage of the octane you are just throwing your money down the drain. Any help here would be great. I asked the dealer about 91 and he said it would be ok just a little loss in performance would not hurt the engine.

Also, alot of race fuel gets the higher octane by using MMT in their blends. In the manual it says not to use gasoline with MMT in it. MMT supposedly damages the catalytic converter. Any advice on this also.

Thanks for you help in advance


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What brand is the 100 Octane...if it is VP...good to go. Yes you can mix it to get your 93 min. As the dealer said it won't actually hurt to run 91, just ECU will retard timing to prevent knock. Probably a waste to run straight 100 (although that is what I run all the time).

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This is regarding MMT in gasoline. The owners manual says not to run gas with MMT. Even though it says not to is it OK? I beleive it damages the catalytic converter? Does anyone know if VP has MMT in it?



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MMT is not a leaded based product. It is just a way that refiners use to get Octane. Queston is do you know if VP contains MMT?


Once again it depends on the type. The 100 octane VP has no lead. See here:


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