sorry, I didn't see that

4.060 bore
3.85 stroke

H273CP pistons (book shows 8 cc's in valve reliefs)

.018 deck clearance.

Adding in a felpro 1011-2 gasket (.039 compress thickness x 4.1 bore) I get the following

60 cc heads - 11.177

64 cc heads - 10.693

68 cc heads - 10.254

72 cc heads - 9.853



Refigured with Felpro gasket # 1134 - (.041 compressed thickness, 4.18 bore) I got it to drop slightly a little bit

60 cc heads - 11.078

64 cc heads - 10.604

68 cc heads - 10.173

72 cc heads - 9.778

Refigured again with Felpro gasket # 1137 (.053 compresed thickness x 4.21 bore)

60 cc heads - 10.734

64 cc heads - 10.291

68 cc heads - 9.886

72 cc heads - 9.516

It averaged out to .25 more compression with the .060 overbore.
Here is a link to the program I am using. the page discusses Dynamic compression and its importance. The program figures both Static compression and dynamic compression. Look near the bottom of the page for the program link. http://www.empirenet.com/pkelley2/DynamicCR.html

 

whoa buddy where are you coming up with almost 12:1? I thought we decided it was like 11.2:1.... ? I see you're not a huge fan of the high CR but I built a 351W last year for one of my buddies and it ended up like 10.4:1 with iron D0OE heads and he's got about 5000 miles on it and he drives it HARD without any problems. Just doesn't like to start when its warm lol.

 

What cam or should I say what rpm range is this motor going to be run at.... get that figured out and then build the motor with the recommended compression givin by the cam for that rpm range. If the motor is going to spin 5000 tops then you might want to keep the compression down to near stock.... but if your spinning it to 7500 you might want to run say 11to1

all depends what the cam manufacture recommends for compression...

Ive had a few friends and myself for that matter build motors with to much compression. only thing you can do to correct it is run bigger cams or rebuild it to a lower compression. Plus the cost of fuel these days..... anywhere around 8.5 to 9.5 would be where I would shoot for....if it's a daily driver on cheap fuel with a small torque cam....

 

Hey Wreckit87, I don't know where I came up with 12:1 either. Still think you might want a lower CR, though. Have you gone to the link Redtires019 left on the bottom of reply #31? That's some interesting stuff that I'm going to look into further when I have more time and energy. It's something I had never heard of but makes a lot of sense and could really help me with my cam choice (I have 2 already). It would probably help with yours, as well as whether to run with your present anticipated CR.

 

it all has to match.....

 

no i haven't yet but i will. Actually i found a set of AFR 185's yesterday with 72cc chambers!? and he wants like $900 for them so i think ill just go that route. I ran the #'s and came up with 9.9:1.... Perfect.