Max compression on 93 octane?

[db]

Can the 10.5:1 pistons be used with 93 octane? Or is that to high?

 

[jasonp]

I have JE 10.5:1 piston and I have around 175 psi cranking compression. Works good on premium, 92-93. I've used 87 before but reduced the timing. Still ran good.
210 psi is maxium for pump gas, you have to run 93 octane. I believe 12:1 piston will get you there.. personally though I've read that most people use half and half mixture of racing fuel and pump to get this to work as this being an air cooled engine, heat is a big factor starts to become a big factor as this then leads to detonation.

 

[paulie1959]

You dont want to go any higher then 10.5:1 on air cooled engines even at that I would use an oil cooler, there is alot more HP gains going from 9:1 to 10.5:1 then going from 10.5:1 to 12:1 and ther is alot more heat at 12:1

 

[dave76]

I ran the old 11.1 JE piston without a problem, and I'm talkin 95°F heat killin it at the sand pits. I also had a Megacycle 252X1 cam so that bleeds compression a bit. I'm at 230 PSI hot and have no problem with the 446. Don't worry so much about static comprssion, worry more about cylinder pressure, I wish DSW would do a compression test on his 12.1 motor then we can get a good idea on cylinder pressure with that piston.

 

[boxhead]

Even mid grade will work decent, overall it depends on the other mods you have. A full race cam will drop the cylinder pressure a little, so you wouldn't need quite as much octane with one. My good friend runs regular in his z with several performance mods without a problem (at least 11 to 1 compression), even when the book says to run premium. There is no detonation going on at all though. The only way you'll need more than pump gas with 11 to 1 is if you supercharge it, or use nos, which I doubt you are. To much ignition advance would be the the only other possibility.

 

[db]

This was just a general question I had incase I needed to change the piston. I had really low compression that ended up being a valve issue. I don't plan on many engine modifications unless things break, then I'll upgrade it as much as feasible.