Racing Fuel---to mix or not to mix

[Wendell #527]

I'm running a VW 1835 with unknown compression. The previous owner says to run 50-50 110 octane and 92 octane, and that it will run cooler that way rather than 100% race fuel. I always thought racing fuel would just allow the fuel to ignite at higher compression or more advanced timing. I thought it wouldn't make a difference if you had too much octane rating. Would it really run hotter with 100% race fuel?

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[lstrong]

a lot of people "mix" fuels together but they really don't mix.Different fuels have different specific gravities and won't mix together.It creates hot spots in the combustion chamber that could lead to engine failure.I have had some discussions on various forums with chemists on this subject and the only answer I have ever gotten was "don't do it"

[lstrong]

just run what ever octane that keeps it from pinging and watch the oil temp.

[amr126]

in reference to questions above, does that mean your better off with octane booster, since additives are the only thing raising the octane? I've never heard of fuel mixing causing trouble due to incompatability. I'd just like a little more explanation.

[lstrong]

just use a racing gas with the proper octane.try 100 octane and go from there.check your spark plugs often for signs of pre-detonation.Also,most octane boosters are crap.they say 5-7 points of octane but they are really only adding .5-.7 points of octane.
The best octane booster for the money is berrymans b12 carb cleaner.It has toulene,xylene and other octane adders in there for a fraction of the price.google the ingredients.You will be surprised. your still only going to gain 1-2 points with that though.Just use racing gas,it is safer

[redmist]

A 50-50 mix will almost certainly yield a different octane rating from each mix. Petrol when refined doesnt yield the same octane rating each time. Additives such as Toluene are added to raise the octane rating to a pump saleable octane. Dilute these additives by mixing fuels and you may end up with a high octane rating one batch and a low octane rating the next. Simply put, if you want maximum performance, don't mix fuels.

[bajaxp]

I know that some 76 stations sell 100 octane 'racing gas' that is expensive, but not as much as drum race gas.

Also I have seen guys run very high octane race gas in standard engines and found out that they make less power. This is due to the race gas burning so slow in the lower compression engine that it actually mostly burns in the first part of the header pipe. This is obviously not a problem in a high compression engine.

You might want to do a simple compression test and call an engine builder such as FAT and ask them some opinions on your results.

[bajabird]

I just spoke with Greg at Fat. I have an 8:1 fat motor in my prerunner and have lots of race fuel to burn. He said "no problem using better gas in the motors" "just dont run lesser quality in the high compression motor". As for mixing fuels. No problem, I can mix mexicos magna with the sunoco 110.

Thank you for starting this post. I feel more comfortable running my race fuel in the prerunner now. Though it is a huge waste of money!

[Chase 2]

a lot of people "mix" fuels together but they really don't mix.Different fuels have different specific gravities and won't mix together.It creates hot spots in the combustion chamber that could lead to engine failure.

Whaaaaat??? That is not even close to correct. All Gasoline range fuels are blends of hundreds of compounds in the C5 to C12 range. Those compounds typically include Benzene, Toluene, Ethyl-benzene, Xylene, Pentane, Heptane..... and on and on along with each company's own additives. The specific gravity of the gasoline is dependent upon the ratios of those compounds and has nothing to do with their ability to mix. To go further to imply that the inability of two gasolines to mix such that they burn at different rates in the combustion chamber is complete bull. Besides complete mixing in the fuel cell/ gas tank, the atomization of the fuel in the carb or injectors will effectively blend your supposedly non-mixable fuels.

Now, it is possible that there could be a race fuel that has an additive that could be incompatible with other gasolines, but that is far, far from what you are saying here, and I've yet to see it.

I've been running blends of pump gas and race gas for years with great results and no problems what so ever.

[Ramsey_ElWardani]

I ran four different fuels in this years Baja 1000, anything I could beg, borrow or steal, and couldn't see a difference in AFR or EGT. They mixed well over the bumps, shaken not stirred.