What octane does a 91 305 tbi and auto trans with cold air induction run best?I have 87,89.5,90,91,92 and 93 available in my area.Does it matter if the fuel has ethonal in it?I`ve run 89.5 in it at the track and ran 15.50 @87.7 mph.

 

Welcome aboard. There are many things that will effect what octane to run. With 0* or 2* base timing you should be able to get away with 87. 4* or 6* will usually require 89 to 92. Cooler temps will allow you to use a lower octane as well. There is no need for 92 or ultra 94 or any type of ocatne boost. Using that will only delay combustion and could cost you power.

 

are my e.t and mph times good or bad?

 

Sounds about right for a stock 305 TBI.

 

how much of a difference will the ultimate throttle body mod make in et and mph?

 

It doesn't add much, but in the long run every little bit addes up. Take a few minutes and read the "new to TBI sticky" at the top of this forum. There are all kinds of stuff in there about octane and ultimate mods and such.

 

It must be cool to have 93 octane available at the pump. Here in SoCal 91 oct is the most. The highest compression anyone runs here with pump gas is 10.5 (with Al heads). I bet you can run almost 11:1 cr with 93 oct gas and Al heads.

 

LS2 = 10.9:1

 

Actually those are perdy dang good. Not a whole heck of stock LO3's in the mid-to-low 15's. Then again, from the look of that pic, you've got a couple goodies

Bruce (90RS305)

 

Thanks 90rs305.I was considering running 87 oct to see if it might go any faster.Doesn`t 87 have alittle faster burn rate than 89.5?The car came with a dynomax muffler and dual exhaust.I looked up the muffler in jegs,and sounds like a pretty good flowing muffler.However,I want alittle more of a muscle car sound and was considering a flowmaster or aerochamber muffler.I like the sound of the flowmaster,but would prefer the flow of the aerochamber more.Do you think either of those two mufflers would add any power?

 

yes, the lower the octane, the faster the burn rate, or you could say it is more 'explosive', the only reason to run high octane is the detergents, I do run a few tanks of 92 through my car every year, but I run 87 98% of the time. With only 9.3:1 compression, there is no need for anything more. BTW, the best times I ever ran stock at the track, was with 87 octane, and 4* of timing.

 

I've run nothing but 91 octane in my car. Reason being, the few tanks of 87 that I HAVE run, dropped my gas milege WAY down. Didn't notice and difference with the butt dyno, but the milege/$$ ratio is alot better with 91 for me. Now i've got 2* advance, so from my understanding I don't wanna run anything less...

Bruce (90RS305)