Octane question
 

Hey all, I've been noticing that a lot of our BP stations around here are getting rid of their 93 (10% ethanol) and replacing it with 91 (100% pure)

So my question is, with higher horsepower levels, which would be better? 93 with 10% ethanol or 91 pure gasoline? I run meth as well.

You will need to take out some timing.

93 with 10% is less prone to knock than pure 91. Agree with ted, drop the timing.

93 e10 is better than 91 as the two nice guys above said.

Nothing 16oz of Torco cant take care of when added to 12-13 gallons of 91

Thanks guys

Why? Do they start with 93 octane gas and add 10% ethanol? If so, I would agree with the others above. Or do the oil companies factor in the higher octane rating of ethanol and blend it with a lower octane of gas to achieve 93 octane? Not doing the math, but would think that the gas would be around 92 octane for the blend, if that's how it is done, so still better than 91 straight.

Actually the specs are about 2 points higher leaving the refinery to leave some margin of error. 93 Amoco Ultimate is 95 when it leaves the blending station in the refinery. The gov't frowns on the octane being below the r+m/2 at the pump.

The ethanol is splash blended at the terminal into the trucks. We refine gasoline and buy the ethanol, prob why BP is getting away from it.

Ultimate USED to be shipped in it's own tankers exclusively when it was still Amoco to keep the quality up, not sure that's the case since BP bought Amoco in '99. Too easy to get some dilution with leftovers (87) in the tankers.

Question for the OP...Do the 91 pumps still say Amoco Ultimate up there? Might be coming from a different refinery.

I haven't checked, I'll have to pay more attention next time. All I know is that 3 BPs that I use to go to for 93 all changed over to this "pure" 91. Which I'm not too thrilled over. I may start putting some race fuel in.

You could always splash in your own ethanol with E85 to raise the octane a few points.

There is a calculator online at http://www.intercepteft.com/calc.html to determine the octane/percentage blending your own.

The stock fuel system can handle a 1:1 blend (E47) but you need a tune for anything over around 30% ethanol to keep from popping a CEL for excessive positive fuel trims. The fuel trims adjust for the extra fuel needed after driving a few miles and the fueling carries over into the WOT fueling for positive fuel trims also. I ran 30% E with no issues when I was stock.

Avoid leaded race fuel as it will destroy your O2 sensors over a short time.

I'm far from anywhere near stock. My 02 sensors are tuned out. Running the squash return style fuel system. I'm going to be running two tunes. Ones on pump gas, other is pullied with c16. I'm just trying to figure out what I should run for pump gas. I'm going to have to search around and see if there's any place around here with 93 still.

Your O2 sensors are "tuned out"? Huh? Not completely; how does the system monitor your AFR? Do tell.

He could have a speed density (VE) tune and not use the O2's. Guess we should have read his 7 page build thread. :-/

SD has nothing to do with not using O2s. He could have the tune locked in open loop. I've seen it before. Not sure why some people do it unless it is a race car, but it is easy to disable closed loop feedback and just run it that way.

Why not just order 5 gallon jugs of Torco Accelerator. You add 16oz per 12 gallons and your up from 91 to about 94 octane. Do a search on corvette fourm. Lots of guys swear by the stuff. I was tuned with 93 octane mixed with 16oz for an intank octane of 96. Have no complaints.

5 gallons is about $275 with shipping.....far cheaper than blending in race gas.

Here is just one thread of many discussing the benefits of Torco

http://forums.corvetteforum.com/c5-f...ane-boost.html

Ahhh...I forgot about that conversion. Thanks.