I can run 10:8.1 on 91 octane in my 396. Cam is debatable by some if it's too small. 232/242 .544/.560 110 LSA w/ P&P LT1 heads.

I personally don't run anything less than 93 though.

 

there are many people at 500FWHP that don't have anywhere near 13:1 compression...hell with an A4, 500FWHP is only about 400RWHP and you can do that without touching the bottom end of the motor.

 

Im running around 11.4,11.5:1 on 87octane with only a hot cam

 

I'm Running 12.5:1 on 92/93/94 with no problems. I have no doubt that if I went to race fuel I'd get a nice bump in power. But I haven't had any problems w/ the 12.5. I've also heard a lot of it also depends on your elivation.

 

How many of you guys running high compression have had it all cc'ed and know there exact compression ratio? Most heads are not exactly on as far as the combustion size goes. I've seen edelbrock heads for mopars, new straight from the box anywhere from 80-90cc, pretty big difference!

From what I've learned over the past few years, 10.5 to 1 with iron heads is fine with a decen tsized cam. Aluminum heads will kind of bleed off about a full point. So 11.5 to 1 is pretty safe. You could probally get away with 12 to 1, but its pushing it. So I agree with the 11.5 to 1 number, just be sure to run at least 92 octane.

 

rev cooled also bleeds off another point.
I'm going to run upto 12:1
i'd go to 13:1 if i could, my cam bleeds plenty

 

I know my compression is correct. I gave my entire motor to the machine shop and told them I wanted 12.5 and didn't know the head size. They CCd the heads and then ordered Pistons accordingly(which were custom for the compression I wanted and rod size). I've had no problems at all running normal pump gas. Now I will say I think that I'm not getting full power in the higher RPMs in 2nd and 3rd gear as far as racing it(so I dont really). The only reason I run pump gas at all is for travel trips. If I know I'm going to do racing, I'll fill the tank w/ race fuel. Though the car has pretty much been down, and I only have 436 miles on the motor.

Now running the compression I run, the machine shop said to just turn down the timing a little bit when I drive on the street. I haven't done that yet and really dont have any problems. I'd say 12.5:1 isn't for everyone but can be done. I have a friend that runs 13:1 and he also has no problems, but always uses 94 and does the same as me 94 to get around, race fuel when racing..

If cam size makes a difference then that could be helping us. We both run large cams.

Jason