I read that the Evo8 requires 93 octane fuel. Here in California I can't easily get 93, 91 is about the limit. How would this affect performance?

 

91 Octane is the requirement per the official documentation.

Althought early indications seem that the car's doing much better with 93 octane or higher.

 

With 91 I would suppose the Evo would just retard timing to adjust to the lower octane fuel. Buy octane booster ever now and then for that performance kick on track days, etc.

 

Depends on what 'octane booster' you are talking about. If you are talking about buying those little bottles of 'NOS octane booster' or other brands that come in like 16oz bottles, dont bother. They will bump your octane from 91 to maybe 91.5.

The only real way is to either buy racegas and mix it (or run it straight), or to make your own racegas.

There are several threads on www.dsmtalk.com discussing how to use xylene and/or toluene to make you own race gas. These products have an octane rating of 114-117 octane, so mixing them with gasoline (1part xylene/toluene to 2 parts gasoline is the maximum mix) will net you ~99.5 octane (given a 30%mix [max] and a total of 15 gallons). Toluene and xylene are not extremely expensive as you can find them for about $5-$9 per gallon or $25-$30 for a 5 gallon drum at many paint stores. I do urge you to do some research if you are interested in using xylene and/or toluene to make your own racegas.

 

Anything up to 30%. Of course 30% yields you the maximum octane rating.

One word of warning that I really should throw in here is that if you use xylene or toluene, you need to add some 'marvel's mystery oil' to the mix. Add about 1 oz of MMO for every gallon of race gas that you make (ex: if you make a batch of 5 gallons at 30% mix then you add 3.3-3.5gallons of gasoline, 1.7-1.5 gallons of xylene or toluene, and 5 oz of MMO).

Xylene and toluene, which are both already found in gasoline, do not contain extra lubricants and they act as solvents/degreasers. The MMO provides adequate lubrication to protect your fuel system (pump, injectors, lines, fittings) from the harshness of the toluene or xylene.

 

where can u get this 'marvel's mystery oil' from??

 

how is 98 RON equal to 91 pump octane, the way i calculated its more near the 93~94 mark.... 91 octane, lasttime i looked, was near the 94 RON

 

I have run four tanks of 91 octane mixed with Xylene in my EVO. I use one gallon of Zylene (117 octane) mixed with 11.5 gallons or 91 octane. My car runs smoother and gets better gas mileage which indicates to me that it is running like it was designed. I am going on the dyno next week and I will let you know how it comes out.
I have also run mixes of VP103 unleaded also to produce 93. It works fine but I can't afford it for a daily driver.

 

Also might consider Torco Accelerator. Comes in 32oz. cans and raises pump gas to whatever. One can raises 20 gallons to 97 octane, or higher. Evos like octane. can order through Dan Wall 1-800-769-7582

 

Please be aware of how octane boosters are rated.

Raising your octane up 5 points and 5 numbers are 2 different things.

10 points equal 1 octane number.