Snopczynski Posted June 6, 2009 Report Share Posted June 6, 2009 I want some replies below on where people think it is, or where they voted too. Especially from the seasoned motor guys and our resident builders like flotek, jeff from fast, Daj, Firehead, Blowit, and our buddy out in Nevada. I voted 170 psi. Quote Link to comment Share on other sites More sharing options...
Overboost Posted June 6, 2009 Report Share Posted June 6, 2009 I also voted 170 because I am running 20cc domes and have 150psi and do not run straight race fuel. I run a 30% race fuel mix just for a precaution but have run pump 94 and had no issues. Quote Link to comment Share on other sites More sharing options...
shanYE west Posted June 6, 2009 Report Share Posted June 6, 2009 Usually when I get into the 160's I'll run straight fuel. Timing wans't mentioned so I was assuming it was left at 0, . There are other factor that can promote detonation besides compression.. But I'll just stick to the question. I voted 165. Quote Link to comment Share on other sites More sharing options...
FASTOYS Posted June 6, 2009 Report Share Posted June 6, 2009 I voted 165 cutoff for Prem. gas w/4 degrees timing. I have run 170 w/4 degrees timing BUT you have to have it jetted on the rich side, and you have to have GOOD Prem. fuel (out of a tank that has its own designated fuel hose , not a fuel station that has one hose does all three 87,89,93 etc. as you may get some of the 87 fuel that the last guy pumped out. Some other variables that come into play are squish band width/angle, dome shape, etc... but for the general answer 165 is cutoff. Quote Link to comment Share on other sites More sharing options...
shanYE west Posted June 6, 2009 Report Share Posted June 6, 2009 Ok, Jeff wasn't as lazy as I was. Good info :thumbsup: Never thought about the pump hoses though.. thats very good point.. So probably about a gallon or so of your 93 is 87... Quote Link to comment Share on other sites More sharing options...
FASTOYS Posted June 6, 2009 Report Share Posted June 6, 2009 Yes sir about the 87 fuel! Amoco Ultimate is a good choice as they usually have their own hoses for each octane. Quote Link to comment Share on other sites More sharing options...
toolman Posted June 6, 2009 Report Share Posted June 6, 2009 I have run 170psi on pump gas(93) for several years no issues. But i keep breaking second gear? As matter a fact I have to tear it apart now to find out what's wrong make a popping noise in second. Quote Link to comment Share on other sites More sharing options...
dirtydownunder Posted June 6, 2009 Report Share Posted June 6, 2009 air temp is another factor, motor's in cooler climate's can get away with running a not as high octane fuel. Quote Link to comment Share on other sites More sharing options...
Snopczynski Posted June 6, 2009 Author Report Share Posted June 6, 2009 Yes sir about the 87 fuel! Amoco Ultimate is a good choice as they usually have their own hoses for each octane. Jeff, So your vote is for 93 octane at 165 psi, or 110 octane at 165 psi? Quote Link to comment Share on other sites More sharing options...
FASTOYS Posted June 6, 2009 Report Share Posted June 6, 2009 165lb or below and +4 timing setup correctly i recommend Prem 93 octane. Anything higher or more timing etc. requires more octane. IMO THis is with a GOOD Snap On guage as i have seen many many guages read waaaayyyyy off from the Snap On guage. Quote Link to comment Share on other sites More sharing options...
2001Stroker Posted June 6, 2009 Report Share Posted June 6, 2009 10.5:1 Quote Link to comment Share on other sites More sharing options...
AWR Posted June 6, 2009 Report Share Posted June 6, 2009 165 Quote Link to comment Share on other sites More sharing options...
AKheathen Posted June 6, 2009 Report Share Posted June 6, 2009 well, damn, the question is to simple for me to vote definate. i know i would personally switch to strait race fuel around 175-180, but that doesn't account for abmient conditions such as heat,humidity, nitrogen content, or flow iinfluences, such as the exhaust charge or crankcase/intake efficiencies. of caurse, timing, too. the cranking compression really only gives you the condition of the cylinders in regaurds to the compression ratio. it's like asking the same question on a car that can be running n/a, or up to 30# of boost, but not specifying which. you can have 40# difference in cranking compression in 2 different engines that have the same octane requirements. also, are you asking which point you start loosing power from lack of compression for the fuel? :shrug: Quote Link to comment Share on other sites More sharing options...
2/2 many banshees Posted June 6, 2009 Report Share Posted June 6, 2009 I run 102 octane with 175 psi compression. Can I cut it down alittle with 93 octane? Quote Link to comment Share on other sites More sharing options...
Snopczynski Posted June 6, 2009 Author Report Share Posted June 6, 2009 This isn't hard, I have seen a lot of guys on here answer this question with little to no info about timing, squish, etc...... Just answer off general rule of thumb for compression vs octane. :wallbash: (if you guys wanna get technical) 9,500rpm dune port motor, 0 degree timing, .045" squish, 75 degrees ambient temp, 72% humidity, 30.01 barometric pressure, at sea level, and 0 pounds of boost! Jeff (Fast) So what compression for the cutoff to go to straight race fuel. Im not worried at the point where you think the need starts for higher octane. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.