Quick Ranger

iTrader: (2)

What's the max CR you guys are running on pump gas with carbs? I know the EFI guys are getting away with up to 12:1.

CrashTestDummy

iTrader: (1)

It shouldn't matter whether or not you're running carb or FI as to the max compression you can run. Max compression you can run on a particular fuel is determined more by the shape of the combustion chamber and cam timing.

newschool72

iTrader: (12)

It can also be in the engine controllers ability to back the timing out at the first sign of knock. IMO that is the only advantage the bigger ECUs have over the carb stuff. The ECU will allow max timing under ideal conditions, but back it down if conditions aren't right.
Cam timing does have a huge effect on the static compression you can get away with, but when the engine finally gets to max torque (max efficiency ) the spark knock will come in with say, a fat duration cam. Dynamic compression is what has the major effect on whether or not you can run on a certain fuel or not, or how much lead you can run in the timing on a particular fuel octane .

dogsballs

run e85 and go wild 13-14:1

speedtigger

iTrader: (16)

Another consideration with higher compression on a carbed motor is "engine run on". I have 10.9:1 and if I run 87 octane it will run on a bit on a hot day after the key is turned of. Unlike fuel injection, a carburetor will keep delivering fuel even after the ignition is turned off. So, if you get the compression too high, you may experience run on where you would not with fuel injection.

Quick Ranger

iTrader: (2)

I think i'm going to go max of 10.5, sorta like i used to on old sbc with alum heads. I know EFI is easy to tune for higher CR, i was trying to see what alot of you guys were running.

speedtigger

iTrader: (16)

After running 10.9:1 for a couple years now, I personally would not be afraid to run up to 11.5:1 with the right camshaft.

wildcamaro

iTrader: (15)

Yea my car is only 10:1 and it like to run on its own after I shut it off lol...

3pedals

iTrader: (3)

I ran 11:1 on 91 octane with an agressive cam, no problem.

TXsilverado

iTrader: (18)

i'm around 11.7:1. does fine on 93 but i tried 87 just messing around in the driveway and when i turned it off it dieseled for about 20 seconds (which seemed like 20 minutes lo)