So im going to the track this weekend for the first time, and having a blown crate motor with hypereutectic aluminum pistons in it, i wouldnt mind running a few gallons of race gas. The local sunoco carries what i belive is 260GT race gas at the pumps, the only thing that makes me nervous is its oxygenated - Will this effect the tune? All im trying to do here is avoid detonation seeing im not running a knock sensor.
9.1:1 CR, 6PSI@5700 and it pulls 1* of timing for the first 4PSI, pulls 7 total (32-7=25) @6PSI

http://www.sunocoracefuels.com/fuel/260-gt

 

What you have to look out for is the stoich rating on the different race fuels. For 260gt it is 14.1, and normal 93 octane is 14.7. My O2 sensors don't function, so i can run leaded race gas which is closer to the 14.7 normal pump gas stoich. If you are running a wideband O2 sensor, what you see on the sensor with a full tank of race gas won't be accurate. For mixing a few gallons with pump gas, not sure if it would be worth the effort if you really don't need the octane. At 9:1 compression, i don't think you need the octane, but that is my $.02.

Here is something i read a while ago from the 'net about race gas:

AFR: Air Fuel Ratio

Stoich Rating: In simple terms is the AFR to have chemically complete combustion that is neither rich or lean. For Example most pump gasoline is about 14.64 to 1. Which means 14.7 parts of air to 1 part of fuel.

Lambda: Is a term that is utilized when tuning. In basic terms think of it as an adjustment to your stoich rating when tuning AFR. For example with pump gas tuning .80 lambda, 14.7 x .80 = 11.76 AFR target.

Lets assume your car blower car has a nice tune that gives a perfect 11.8 AFR under WOT with pump gas.

So now it is race day. We add some timing to our tune, drain the fuel tank, and fill up with some high octane unleaded VP109.

We go for a blast down the 1/4 mile while datalogging and see the A/F is reading 12.8 then make a quick trip to the bathroom only to find out they are out of toilet paper.

There are a few factors here to consider.

The stoich rating of VP109 is 13.41.
Most wideband A/F modules are calibrated to 14.7 pump gas stoich.

So this is the formula to determine the true A/F for the run.
AFR/Wideband Stoich x Race Gas Stoich
12.8/14.7*13.41= 11.7 AFR on Race Gas

So you may think 11.7 sounds safe but we must remember the VP109 stoich is 13.41. So 11.7 AFR = .87 lambda. For the most part a safe lambda value is .80 to .82 for a forced induction mustang. I prefer .80

So we take VP109 stoich of 13.41 x .80 lambda = 10.73 AFR
This is the AFR (10.73) I am tuning for.

Keep in mind this is not what will display on your wide band as it is programmed to 14.7 stoich. You must convert the AFR.

AFR/Race Gas Stoich*Wide Band Stoich

10.73/13.41*14.7 = 11.76 AFR is what I want to see on my wideband when running VP109.

Just to reiterate 11.7 on the AFR display with VP 109 is really a 10.7 AFR.

 

Oxy fuels do require more fuel to be safe than non oxy fuels

Also alot of injectors do not like oxy fuels. So use sparingly and get it out the system after you are done, and go back on pump gas

 

Ive been doing some reading and it looks like if i run 5 gallons of 93, and 5 of 100 octane it puts the octane rating at about 96.5 - Im not looking to run straight race gas, but again, i wouldnt mind a little more peace of mind.

Car pretty consistantly runs a 12.5 AFR under full load while in boost, So your saying the gauge is gonna read off (or still read a 12.5) and its actually gonna be more rich with a mix of 100 octane? That i would be fine with if im understanding correctly.

Its a daily driven street car, so i doubt even a full tank would last me a week haha

 

If stoich is higher than pump gas then you can possibly lean out the afr reading to be optimal. Oxy fuels usually are richer stoich than gas so you may want to add fuel to lower afr reading to be optimal

With those pistons and a full pull, you should be looking for closer to 12:0 air fuel imo to be a little cooler in the chamber. 7 deg pulled should be ok but let the plugs tell you what it wants, or track mph

 

Just increase your target air/fuel at wide open throttle a half a point richer. Consider a knock sensor though later on because all it takes is a carbon filled injector at wide open throttle to run a tad lean, and by then it is too late for that cylinder under boost pressure. Looking forward to your results, is this the weekend you're meeting up with Joe...?

 

I won't be making it this weekend. Maybe next year.

-- Joe

 

Damnit joe!

Fuel trim adjustments stops when it reaches boost, but i logged it today on lunch and it was in the 12.2-12.5 range at .

 

What problem do injectors have with oxygenated fuels?

 

Depends on the injector construction but there can be an internal o-ring that will swell when in contact with mtbe in oxy fuels. It can reduce flow by 30% or more