FuzzyDiceRule

First off, can anyone tell me a ballpark on what my compression ratio is with the 58cc combustion chambers?. I dunno when it was running, a couple times it felt like it was pinging a little bit, granted it still has a tank 1/4 full with 87, that will change, i will either run 89, or get a 91 tune. what exactly do i have to do for that, just get it filled up with 91, and just get a shop to do a dyno tune with it? how much will it cost?

mjr46

throw some cali crap 91 one in it, we got 93 here, anyway and maybe some octane boost to be safe but compression will be around 9.6 to 9.8 as it stands

67mustang302

You need to know piston dome/relief volume, deck clearance and gasket compressed thickness/bore to be accurate. And even then CR will be altered by how large the valve heads are and how much they hang into the chamber when closed(if you want to get REALLY accurate). Also static CR doesn't mean jack really, dynamic or actual compression is what matters. You could have an engine with a static 10:1 CR that's only 5:1 actual(50% volumetric efficiency) or an engine with 9:1 static but 10:1 actual(111% volumetric efficiency).

That's why some high compression engines with large cams can get away with running on pump gas but modest compression engines with modest cams may not. Actual compression will be dictated by head/cam/intake choice as well as exhaust etc. Your setup is similar to mine, and mine won't tolerate less than our Cali 91 octane, and that's with only 31 total timing, a bit of extra fuel and 9.44:1 static CR. Get a 91 tune, otherwise you'll prolly be leaving a fair bit of power on the table, especially with the crap we have at the pumps out here.

FuzzyDiceRule

im gonna get the 91, i just wanna be prepared for how much its gonna be, i guess it depends on the shop eh?

i started it earlier and when i gave it gas it hesitated like a som bitch, this thing is more cold blooded than the mach 1..., the hesitation went away after i let it idle for a minute...

primetime5.0

im running 91 with 10:1 compression and 14 degrees timing.. no issues