Thread: speaking of correct octane fuel????????

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what is the correct fuel to run through a 12:5-1 compression motor. i use 110-114 but i am wondering if i am wasting my time and 104 would work. only reason being is you have to order the lower grade as 110-114 are on hand. so dave and tech whadda ya think?!

Ever find an answer? I'm trying to find some info on CR/octane.

Scooter, it's pretty much impossible to say because the fuel required is not dependent on static compression ratio, it's dependent on dynamic compression ratio and you don't know what that is until you run all your data through a DCR calculator.

Even after you've determined DCR, there is so much conflicting information out there about what works with what and what doesn't that it will just confuse you.

I suspect that the only bulletproof way to tell would be to bolt up a rattle detector on the side of the block and try decreasing grades of fuel until the motor detonated.

I can't remember who it was now, but someone on here was saying that he ran a PSI of 200+ on pump gas with everything polished internally to prevent hot spots, no PCV or EGR to pollute the mixture and a very tight squish.

In your case, is there that much difference in the cost of fuels that would cause you to investigate the limit of the fuels?

Scooter,

I ran Sunoco 260 (104 Octane - leaded) in my 68 GTO w/ 11.8:1, iron heads. No ping.

the stuff i run is 110-114 leaded i was just wondering about e85 dave got me thinking when he mentioned that a while ago............

104 should be plenty with 12.5, but as Tech said it is dependent on many other factors especially squish and piston top/combustion chamber configuration. I've run 14:1 on 104 with coated piston tops and "massaged" chambers.

As far as E-85, we have a distinct advantage here because we are 7 miles from an ethanol plant and are assured of a supply and good quality minus all the shipping and storage contamination issues. Absolutely nothing worse then e-85 being sold out of an old tank that was previously used for gasoline. The ethanol will work all the contamination, rust, crap, water, and crud out of that old storage tank and guess where it ends up. E-85 works great for us, just be sure of your supply!!!

knowing our local stations i wouldnt buy it until there was an e85 station all by itself lol. there is one e85 station in seattle i beliver its private fleet only thou not public use.hows about e-92? LOL

With the ethanol plant so close we managed to get some e-100 and have been pumping up the e-85, a very slight increase in performance and went up one jet size on both sides of the carb. The Comet and the T-Bird are both doing the 9.90's,,,, Also, but no proof or reason, both cars seem to be more consistent round to round?????,,,,,..