travis6767 Posted August 19, 2008 Report Posted August 19, 2008 I have pro mx port and polish cylinders, with a milled head that has the swirl machined into it, i run plus 4 timing, and i have wiseco pistons, i was just wondering if i should be running some fuel with a little more octane, i run 92 as of right now Quote
dajogejr Posted August 19, 2008 Report Posted August 19, 2008 Compression ratio determines how much octane to run...calculate it. Quote
POORBOY350 Posted August 19, 2008 Report Posted August 19, 2008 sounds like a good set up. how much is it milled? cause i've read .30 you can run 93 octane. but if it is .60 you'd prob need to run 50/50 race fuel & premium. just what i've heard. Quote
mdhc500 Posted August 19, 2008 Report Posted August 19, 2008 (edited) Check your compression. A rule of thumb is anything above the 150psi mark you can/should start running some higher octane fuels. I have 155+ psi and run 50/50 mix of good quality 93+ oct and 110 race fuel. I have no issues thus far... Everyone has their opinions though. I personally run Sunoco 94 oct and Sunoco 110 with some fuel stabilizer in it. Check your compression. Edited August 19, 2008 by mdhc500 Quote
dajogejr Posted August 19, 2008 Report Posted August 19, 2008 That is a rule of thumb...if you don't have EXTENSIVE porting, it will be fine. But you could have a motor with 15:1 compression ratio, but 140 PSI cranking pressure if it has a very high/long duration exhaust. It wouldn't last long with pump gas... That's why race fuel is rated for compression ratio, not cranking compression... Quote
mdhc500 Posted August 19, 2008 Report Posted August 19, 2008 That is a rule of thumb...if you don't have EXTENSIVE porting, it will be fine.But you could have a motor with 15:1 compression ratio, but 140 PSI cranking pressure if it has a very high/long duration exhaust. It wouldn't last long with pump gas... That's why race fuel is rated for compression ratio, not cranking compression... Exactly, that why running a mix is prolly best. As long as you are not detonating you are more than likely fine. A little octane boost never hurts... Quote
travis6767 Posted August 19, 2008 Author Report Posted August 19, 2008 Thanks for the answers guys, but how do i find the compression ratio? Quote
mdhc500 Posted August 19, 2008 Report Posted August 19, 2008 Thanks for the answers guys, but how do i find the compression ratio? Do you run 93 now? Are you getting pinging or detonation? Just do a compression check. If you are anywhere near 150 just do a 50/50 mix and you will be fine. Or you could try this if you like math... Take your Displacement + your Piston Volume + your Deck Clearance Volume + your Gasket Volume + your Cumbustion Chamber volume and divide that number by the Piston Volume + the Deck Clearance Volume + the Gasket Volume + the Cumbustion Chamber Volume... This will give you your current compression ratio. Look at the stock displacement numbers that are all listed in the Maintenace Manual and revese engineer this formula to see the stock compression ratio, and you will see that its correct. Good luck Quote
travis6767 Posted August 19, 2008 Author Report Posted August 19, 2008 i dont have any pinging or detonation, but i just re ringed it and pistons look good, and that was almost 3 years ago that i put those fresh pistons in, and i ran 92 octane the whole time. i just didnt know if the rings should last longer that that, thats why i asked about the fuel thanks for the math Quote
mdhc500 Posted August 19, 2008 Report Posted August 19, 2008 no problem. Just run 50/50 if you are close and use good oil and jet correctly... Quote
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