Originally Posted by Shawnb
That a good point.... I dont know if the high compression is from the pistone or smaller cc heads. I dont know. I assume from the pistons but I didnt build it. I have a build sheet but not with me now. I think it eagle rods and Wiesco pistons. I think iron 2.02 ported heads. If the rise is from heads cc maybe new edelbrocks will lower it... Where I live E-85 is everywhere. I dont care about to 30% more fuel comsumption. I thought E-85 is 105 octane? Based on what I've read it sounds like it might be the best for me to sell it to a racer. Someone said ger a 350 from a junk yard and?? No. I may build anther but not something cheap....
My somewhat limited experience with E85 indicates that an octane rating of 105 is much higher than the performance Iíve seen from it, not withstanding that vehicle weight and gearing play pretty big on compression ratio performance.
That said; if you look at the numbers and the process of determining octane for unleaded pump and leaded race fuel which is taking the fuel and testing it two way one the Research Octane Number (RON) method which always drives a higher number than does the Motor Octane Number method (MON).
When one goes to the tables you find that fuel grade ethanol is rated at 109 octane RON but only tests to 90 octane in the MON test. Since to make a comparison to gasoline octane ratings the 109 and 90 need to be added together and divided by 2 which nets out 99.5. Better than pump unleaded but not the same as high octane leaded race gas.
Then E85ís ethanol is diluted with 15 percent gasoline. If one assumes that the gasoline is a pure petrol premium 92 octane base and that the octane rating of either ethanol nor the gasoline reduces when mixed (the kind of thing that often happens with fuel mixtures) you get ethanol at 99.5 times .85which nets 84.6 as its contribution and gasoline at 92 octane times .15 which gives 13.8 the sum of which only makes 98.4 total octane. Scientific data of the octane rating of blended fuels that makes any sense to my simple mind is hard to find. Everybodyís trying to sell something and distorts the truth with the most favorable numbers they can find and certainly ethanolís high RON number is quoted against gasolineís ROM+MON/2 average a lot and everywhere. Problem where I live is pump gas already has 10% ethanol in it. When I read the blend data from the manufacturers and the scientific communities it looks to me like one of the first things they do with 10% alcohol is use it to raise a lower grade petrol feed stock to the needed octane of sale at the pump. It does appear that this is a situation where more is not better, it looks form the data like 10 to 15 percent alcohol is in an octane sense the biggest bang for the buck. So itís not a clean exercise to figure out what a pure petrol feedstock that would make 92-93 octane without any alcohol and how it would behave when mixed with 85 percent ethanol would really be like. Then consider that 100% fuel grade ethanol can actually be 95% alcohol and 5% water. And if I know the fuel companies at all; you can be sure that looks more like 93 to 7 maybe even 90 to 10 because when mixed with 15 to 90 percent petrol the stuff will burn even with that much water in it. So the other question is how much octane behavior is due to the unknown amount of water injection that comes along for the ride.
My limited experience with E85 roughly tells me that its actual performance in a competition engine when compared to VPís C12 which is rated 108 RON+MON/2 for example is not equivalent to E85ís oft stated 105, 107, 109 octane depending upon the reference source.