what fuel to use?
 

The last track weekend I ran, it cost me 280.00 in fuel for 28 gals of 100LL. This next race, I'd like to enter into 2 classes and am looking to save a buck (or a small fortune) in fuel costs.

I would like to look into other options:

I can cut 110 race gas (8.00/gal) with 50% 92 pump gas and get 100 octane for approx 6.00/gal. (would this cut the lead enough to work with O2 sensor?)

or, I can get 100LL Av gas for 5.65/gal.

I know that there are many racer opinions on what fuel makes the most power, etc. I'm more interested in knowing what the turbo miata racers have found.

What fuel grade have you run successfully/unsuccessfully on the track?

Does a standard race prepped 1.8 running 12# boost even require 100 octane?

Are you tuned for anything above 92? If not, you won't get much more power. You could mix in a little 100 for some octane head room but everything else is expensive exhaust fumes without the tune.

Depends on your tune. I would tune on pump gas, then add 3-4 gallons of 100 unleaded to the tank for safety (or run 3-4* back on timing).

No, the "tuner" that did the map assumed 92 octane. With the 100LL, my EGT's maxed out at 1350 (as measured 6" from turbine outlet).

If e85 is available to you I would use it.

Ever run Klotz?

Around these here parts we have 93 octane so we use it to tune. If I hit detonation, I take 4 degrees out depending upon the IATs when that det occurred. With low compression I think I can run 91 octane on my 93 octane tune because I never saw detonation, but I always take a few gallons of 93 when I go to OK to bring the octane up a little. I have too much money in this car to make mistakes like that.

Go to paint store, buy toluene by the drum, mix, win.
Quick find--> Vintage Triumph Register - VTR
Little bit of info
Formula #1 - Toluene

R+M/2.........114
Cost...........$2.50/gal

Mixtures with 92 Octane Premium

10%...........94.2 Octane
20%...........96.4 Octane
30%...........98.6 Octane

I use to mix 10% in my old 200sx SE-R for completely legal late night weekend races in warehouse districts. I could crank the timing up a lot before det. I don't honestly know how high of a mixture I could go. Quirt (guy i use to work for) said more than 10% could cause issues with the fuel system or filter. Or that was when we were mixing alcohol, can't remember. Now that this has come up I'm going to hunt around for local paint supply shops. I never had any issues, but I didn't run it ALL the time. Just for funs

Can you get a big boy ECU and stay in class? That would be an excellent winter upgrade if it is possible.

"Race Fuel" actually has somewhat slower flame propagation than "Pump Gas." The higher flash point and slower flame front are two of the things that help prevent detonation. but if your spark and fuel maps are not optimized for this there are literally THOUSANDS of back to back dyno runs that show "Race Gas" in a car tuned for "Pump Gas" will actually make LESS power.

And, if you think "Race Fuel" has slower flame propagation, you ain't seen nuthin' 'till you've topped off with AVGAS.

AVGAS is designed to work on engines with huge pistons, long strokes and 2700 maximum RPM. Great octane, but you couldn't have picked a worse fuel for a Miata. Modern car engines try to prevent det by having a well-controlled fast burn. Mazda's Skyactive is one of the ultimate expressions of this.

Anyway, you're much better off with pump gas than with AVGAS. And that doesn't even include all the lead deposits.

I run some AVGAS in the 440 in my Sport Fury (mainly to get some lead to the exhaust valve seats), but even there I cut it. There are lots of old school anectodal stories about hot rodders running a tank of the old 130 purple avgas (designed for B-29 bombers) in their 442/GTO/GTX/fill in the blank and melting their mufflers. That's the wrong place for the heat.

The slow burn might help spool though. Hmmmm . . . .

This.

Honestly if you det on the track with the fuel you were tuned with I would look at your iat and/or ect spark compensation. I bet you need to pull more timing but only under the iat/ect conditions that it happens.

ugh, no it doesn't. Flame speed has nothing to do with octane and everything to do with the chemical compounds in the fuel.

I would think hard about not switching to E85 at this point. Given the current drought conditions effect on the corn crop. E85 might get even more scarce than it already is. Now if this is a race only car that might not matter so much.

E85

I believe OP is running a BEGI reflash on the MSMs stock ECU so exotic options are not in the cards currently. I don't know if his class restricts EM but if it does, he's probably already... ahem... bending the interpretation with the reflash. :giggle:

I have personally witnessed the exact opposite to be true. Doing a run on the dyno with regular Tennessee 93 octane and then filling up with VP Racing street blaze 100 (100 octane unleaded) would net something like 15 Hp/tq on your typical GT500 or Camaro.

As for the OP, if E85 isn't possible, just use pump gas and a few gallons of high octane stuff for safety and adjust the tune accordingly.

That wouldnt be completely strange in a modern engine the difference between 87 and 93 can easily be that much in a car with dual spark maps that are blended based on knock.

Your typical GT500 or Camaro will automatically compensate for the octane increase. His reflashed MSM ECU isn't going to do that.

92 octane E0 is available at the Kwik Gas on MLK across the freeway from PIR. I find that my car likes E0 quite a bit more than E10 - I would get some pinging with E10 that isn't there with E0.

There's no need for 100 octane for you that I can see. Stock ecu (tweaked a bit), and moderate boost levels. Maybe throw in some toluene each tank.