Mixing pump and race gas?

[tekdeus]

I know a few people mix pump gas and race gas to add octane.

My car is currently safe up to 22psi on 94 octane pump gas + water/meth injection. (There was slight pinging at 24psi on the dyno, and we then backed the base timing down 2 degrees)

If I want to boost 25-26psi, should I run a 50/50 mix with 110? Or even C16?

Is there a chart or calculator that shows approximate octane when mixing?

 

[grimreaper]

lets see from memory....

# of gallons of 94 octane * 94 = X
# of gallons of c16 octane * 116 (octane rating) = Y

(X+Y)/ Gas tank size (18.5)= octane level in the tank

50/50 with c16 should net you 105 octane if c16 is 116

do they rate pump gas the same up there?

 

[gofastgeorge]

Leaded race fuels will kill your o2 sensor, so use unleaded only.

 

[juhanis]

leaded fuel rocks. but i'm sorry i dont have anything else useful to say besides that.

 

[Fletch124]

Ive heard from a big Norcal subaru tuner that mixing race gas and meth isnt the greatest idea. Supposedly the 2 potential octanes equal each other out. 50/50 meth lets say raises 91 pump to 108; race gas 110. Mix those and youll supposedly get 109 octane with a cooler intake charge.

Just stick with the meth or switch to 100% meth.

 

[jdub]

Ive heard from a big Norcal subaru tuner that mixing race gas and meth isnt the greatest idea. Supposedly the 2 potential octanes equal each other out. 50/50 meth lets say raises 91 pump to 108; race gas 110. Mix those and youll supposedly get 109 octane with a cooler intake charge.

Just stick with the meth or switch to 100% meth.

You heard wrong or this tuner doesn't have a clue...especially since Brad uses meth injection and does not mix alcohol in the tank. If you want to use methanol or ethanol as an octane booster as you described, you better be thinking about what it does to the fuel system.

The formula Grim posted above is correct when mixing in race gas. It is the same if you use toluene or xylene (much better option than alcohol) to boost gas octane levels.

Leaded race gas is not only bad for the O2 sensor, the CAT is not going to like it either.

 

[Supracentral]

Be sure you're working with the same octane measurement method. There are a couple of different ones. This may help:

http://www.supramania.com/forums/showthread.php?t=97940

 

[tekdeus]

Approx. how much additional octane I will need to go from 22psi to 26psi? (assuming 22psi is currently safe on 94 pump + meth/water).

I know that leaded fuel reduces the life of a Bosch wideband sensor, but only slightly if used once or twice at the track. But is it really bad for the OEM O2 sensor?

 

[jdub]

For octane at high boost...more is better.

Just as bad or worse for a stock O2 Brad.

 

[IJ.]

Mixing fuel is far too inconsistant to risk if you're chasing the ragged edge unless you have some way of measuring the actual octane and correcting the tune based on that! (ie: Flex Fuel sensor + MoTeC)

 

[grimreaper]

^my thoughts as well... run a tank of 116 when you know your heading to the track...

why are you chasing those additional 4 psi? theoretically you could loose some power if your not tuning for the higher octane... (if it were my car id still run it to be safe...)

 

[tekdeus]

^my thoughts as well... run a tank of 116 when you know your heading to the track...

why are you chasing those additional 4 psi? theoretically you could loose some power if your not tuning for the higher octane... (if it were my car id still run it to be safe...)

I was wondering if I could break 500 on the dyno at the upcoming Pac NW meet.

On a rather hot day on the dyno my car showed very slight knock at 24psi, then we backed the timing down 2 degrees and just run 21-22psi. So it just needs a little more octane to get up to 25.

 

[Supracentral]

Also, it is possible to go to far. Higher octane fuel burns slower. I've seen people run too high of an octane and lose power. C16 is overkill for a lot of cars - VP Import is insane overkill. Fuel that has too high of an octane has the same effect as retarded ignition timing.

 

[jdub]

I'm thinking a tank of 100 octane low lead Aviation gas will be plenty.