i threw a tank of 118 in last weekend because i wanted to do some timing tuning for the track and noticed my AFR went way rich. I was commanding 14.65 and it was reading 13.25 consistantly, very odd. Is this normal? Im not talking PE, just normal cruising under light load.

 

yes. you have to retune when you change to race fuel.

i have tried tt114 and it doesn't seem to need any tune change.

tt118 goes way lean and you need to add a lot of fuel

rocket 118 goes a little rich. not a ton but enough you need to pull a little fuel.

every fuel is diferent. that tt(track tech)118 was way diferent

 

Well that should make for some expensive tuning....LOL. Guess i will have to set up 2 seperate VE tunes, one for 118 and one for 93. I was just changing the high/low spark table....i will have to go back and make some thorough adjustments. Thanks Parish.

 

good info

 

timing seems to vary as well. the tt118 needed more timing to not loose power. the rocket118 didn't need any extra timing.

we are running 118 because i had some laying around. unless you are going over 20psi i wouldn't run that high of octane. some 114 would be fine.

since you dont run around on 118 all the time i dont know if you need to nail down your ve tables. you could just make minor adjustments to your pe table or maf table.

 

Different fuels have different densities. There is a constant for that in the PCM. Regular and premium unleaded should be about 720gm/l, but race fuels will be different. On VP's site you can get the specific gravity for most of their unleaded fuels. Injectors deliver fuel volumetrically, not by mass, so correcting this should help.

 

Good point, i guess some PE adjustment is all i really need along with the timing. No MAF here, running a SD tune.