I was at Sears Point today getting a helmet, when I noticed they have several grades of race fuel up to, I think, 117 octane at $7.00 a gallon.

What happens if you run this stuff in your stocker?

Just curious....SP is only 20 minutes from home. Might be fun to run it now and then if it won't hurt anything.

It won't run as good as if you ran the cheap gas. High octane is fine if you have an engine designed and built to take advantage of it, i.e.
more compression, advanced timing, etc

Race gas will burn slower thus not getting all of the BTUs out into energy to turn the crank. It won't burn completely.

yupp, what he ^^^ said ...

higher octane means you can compress the fuel more before it self-ignites.
low octane fuel will ignite premature in a high-compression engine (engine-knock) ...

running high-octane (the 100+ kind) in a stock engine is counter-productive.
the only one who will benefit is the sellers bank account.

the fuel will not burn "clean" in a low compression engine, thus you will,
at best, not feel any difference, at worst, your car will run worse than on normal fuel.


on a interesting side note (someone with better understanding please back me up here):

ever since i drove my first air-cooled car ('72 VW bug 1302) i noticed the following ...

the car runs noticeably BETTER when you mix high octane and low octane roughly 50/50,
but you DO NOT get the same "boost" running mid-octane rated fuel.

dunno why that is, but it was true all the years in germany and i get the same with my 914 here in the US.

maybe different additives for the different octane levels that work slightly better when mixed?

i dunno, but it works
Andy

My Euro pistonned 1.7 seems to be much happier on low octane gas - it's much more powerful and more obedient.

I'll be running on that stuff when I have the subaru motor and I can dial in the settings for it :-)

Fiid.

this was an old trick from the leaded-gas days too -- mix half premium leaded with half premium unleaded and you got a big boost.

it's due to diminishing returns - a little bit of lead increases octane a lot, but it takes more and more for each additional octane number. so you mix a little lead into an unleaded premium that's had its octane number raised with 'other stuff' and the slight 'excess' lead from the leaded premium bumped you a lot.

for the tree-huggers out there, this was in the days when leaded gas was publically available, and being used in no-cat cars. and only for the track.

anyway - the individual octane improvers become progressively less effective in higher concentrations, but mix them with a different base fuel, and you can get some more out of it.

interestingly, i run Sunoco Ultra94 in the 911E -- but mostly because the wonky distributor advance is pulling in a bit too much advance too soon. on the track, where the rev range would be kept where the advance is all-in anyway, i could probably get away with less. probably won't tho :-) ...

Yeppers, Race gas BURNS SLOWER to allow the use of higher CR without negative effects...

In a stocker, it'll run like crap... It is also a higher viscosity and goes through jets and injectors slower. This creates a lean condition, and carbs mus be jetted up for it. I have never tried to run it in a D jet engine, but we have an L jet and it screwed everything up.....

it does smell good, though

i ran some 108-ish unleaded race gas in my CIS GTI and it seemed to go okay but mind you, this is a 10.1:1 water-cooled knock sensor engine and i was turning around 7600 rpm for that event, with spark advance about 4 degrees advanced from book, 100F, 4000' MSL.

i wouldn't expect much in the way of issues in my MFI engine - the injection principles are completely different - but the irony is that it doesn't need it... (but you've gotta ask yourself why Porsche started using MFI in the race cars in the very early 60's and kept using some variant of it for better than 30 years.)

the specific gravity is way different too, which will affect carbed cars if they aren't changed for it. besides jetting, float levels come to mind ...

Thanks, guys.

I'll use the "cheap" ( yeah, cheap ) gas .

Anecdote time--

Many aviation engines are very old designs. Quite a few of them are designed for 80-octane fuel. A number of years back, 80-octane AvGas was discontinued, and owners of aircraft with those engines had to find other fuels to use. MoGas (automotive fuel) could be used, but there was a hefty fee to pay to get the engine certified for it.

So a good number of these guys started using 110-octane AvGas, which was still available at the airport and was a lot easier to get ahold of for them. And they promptly started burning their exhaust valves, as the mixture was still burning on its way out past the valve!! An Airworthiness Directive came down forbidding them from using 110 (and maye 100?) octane in those engines that were designe for 80.

I believe that my grandfather wound up writing up several people who had done this, back when he worked for the FAA.

--DD

Funny, but I ran race gas in my car 4 year ago when I started racing. I did so until Rich Bontempi gave me some great advice.

"You don't need (for all the technical reasons mentioned earlier) anything except 92 in this car, what you do need is seat time."

I know it is hard to believe, but the biggest performance factor, during your first year, is learning to drive.

In other words, the biggest modification you can make during your first year is you.

Education is everything...just like in everything else.

Did you get Hank's book?

And by the way the biggest mistake we all make is starting to modify a car piece by piece, when we should have saved our money and learned to drive. Then when we do know what we are doing, buy a car that was properly prepared for whereever we end up wanting to run.

I say this knowing full well that I would have a hard time "just driving" if I started over again...

that's why i will be at the GGF AX this weekend


of course it's easy for me, i'm the only one in my class
Andy

If you read the MFI manuals it says clearly NOT to run higher octane that spec'd for the engine and that tuning problems may result if you do. This is for the same reason as any other FI system. MFI has no way at all to compensate for fuel that burns differently than it was designed for.

i have, and have read, those manuals. wwe're talking about two different things here...

that manual is talking about high CO numbers when running premium in the 2,4-liter "regular-gas" cars. no injection system can compensate for the way the fuel burns.

all i said was that the MFI is not as sensitive to the fuel's viscosity and specific gravity.