Shanman

So guys I realize E85 is 105 or so octane. Up here in mass its e70 so roughly 99 octane for winter blend I want to run E47 but used the ethanol calculator and see that 1 gallon 87/E10 and 2 gallons E70 is about 95 octane, but with 93/E10 it goes to 97 octane. Basically what I'm asking is it worth the extra 2 octane points since I will be right at E50? From my understanding Ethanol is great when IAT's start climbing, and GM Performance recommends running ethanol when roadracing. But the higher the octane the more timing you can run. Does the Ethanol inhibit knock at higher IAT2's bc of it burning more cool in the cylinder or is Ethanol just recommended bc of its higher octane rating solely? I guess this is the right section

Jesse

iTrader: (4)

Maybe it's just me, but I'd use the highest octane possible. Also don't assume the gasoline will actually be E10. I've seen people test it at 5%. It's an "up to" rating. But as long as you test it before you mix it (or even better mix it in a separate tank first) that'll be irrelevant.

09CobaltSS1

Dammit Shannon, I already told you what you should do.. lol

phatnackySS

the way octane is determined is throe a mathematical function that was intended for gasoline so the octane number when you get when talking about ethnol is kinda superfluous, The power you gain from running e85 has little to do with octane more to do with burning cooler, and the fact that ethanol contains oxygen so its almost kinda like the effect nitrous has on an engine. With that said i run e47-e50 for better economy but i always mix with 93 just because. I run the same timing maps for e85 that i do for e47 and haven't noticed any difference as far as knock goes.

Pretty good read on corn juice Page 2 - NHRA - E85 Fuel Switch - Chevy High Performance Magazine

09CobaltSS1

^^ That's because there's no more energy in e85 than there is in e50. Benefits beyond e50 essentially lay only in cooler combustion temps.

Shanman

I know, I know but this is a little more technical bc of the way ethanol has its effects on IAT's past a certain Temp which I'm almost certain that I will be past 160-170 IAT2's with a 2.9 on a roadcourse. I just wanna be safe and blow my load and not my engine on the track. Thought maybe an GM performance LSJ guru could chime in.

09CobaltSS1

The higher the ethanol content, naturally the better heat dissipation you can get. The problem is, to really technically lower IAT's, you would need to spray the fuel further up in the air stream rather than just in a standard injector port location to allow time for the heat to be drawn out more efficiently.

With that said, running e85 (or some blend there of) isn't so much going to lower you IAT's. It will however lower your combustion temps significantly, which when combined with the inherent higher octane rating, significantly reduces the chance for any sort of detonation. Which is what can ultimately make or break an engine.

Long and short of it. If you truly want lower IAT's, either spray meth, or spray ethanol in your air intake tract post blower.

Shanman

Alright so what im understanding is that even with higher IAT's 160-170's I should be okay bc of the cooling effects of the E. The higher temps in the intake going into the cylinder are pretty much cooled down considerably bc of the E's volumetric cooling ability. So really IAT2's arent quite as important with E like gas. I guess a good controlled test would be to unplug the pump after setting the interceptor to read knock and see what IAT's it starts to pull timing. do several pulls and get the avg IAT2 temp. That way im not going triple digit speeds trying to figure it out. Safe enough and i will lift immediatelly after .5-1 degree of pulled timing. seem legit? I am curious to what kind of IAT's it would take before it would start.