AirborneSilva

I have 8.5:1 right now with 76 cc heads, if I put 64 cc heads on what would my compression ratio be? Thanks

MelWff

I believe it's math, your cylinder volume is X and your combustion chamber is 76cc. So X/76=8.5, X=646cc, 646/64=10.09 so 10.1 ratio. This assumes the same thickness head gasket.

AirborneSilva

Sweet, I REALLY suck at math so I appreciate it very much

MelWff

Wait till someone else confirms my conclusion.

RodgerF

Article in the latest Hot Rod Magazine comparing older Chevy heads vs newer heads says the same thing. Going from 76cc to 64cc heads increases compression 1 to 1.5 points all else being the same. Figure 10 to 1 with 64cc heads.

Rodger

Crepitus

9.56

Crepitus

http://www.kb-silvolite.com/calc.php?action=comp

jb78L-82

About 1 point-9.5 with your combo.9.8 with a thinner head gasket.

AirborneSilva

Thanks guys, I was looking at an edelbrock combo yesterday that got me at where I want to be HP wise and it said that the compression ratio should be at least 9.5 to get the HP rating with their combo... Thanks again for helping a mathematically challenged old troop

AirborneSilva

Thanks for the link, I don't have most of the info they are asking for. The only way I know that it's an 8.5:1 is that's what GM says it is

7t9l82

most likely you will find your actual compression is lower than advertised, that may be a good thing .

Crepitus

I entered 2 constants in my comp program your current chamber cc and 8.5 cr using 355 bore stroke ect corrected piston shape to match 8.5 then changed chamber cc to 64 =9.56 to 1 you could probly pick up a little more with a thinner head gasket like the felpro 1096 mls

Sand Hill 11B

AirborneSilva

I'll take the 9.56

Crepitus

swaping the .037 gasket to a .015 with a 64cc = 10.1 about the same as JB calced

DucatiDon

A 2/58 AlphaGator here.......

AirborneSilva

This is the kit that would get me where I want to be HP wise with that compression ratio.

http://www.jegs.com/i/Edelbrock/350/2098/10002/-1

63mako

Trust me it won't get you those numbers. Lucky to get 350 and if your gearing isn't right it will be real disappointing.
The advertised duration on that cam is 308/318.
Duration @ .050 is 234/244.
This is a bigger cam than I have in my 10.5 to 1 383 with 6 speed and 4.11 gear and mine as a hydralic roller.

REELAV8R

One thing I can tell you is that advertised numbers are not totally accurate. On my 77 L-48 it was supposed to be 8.0:1 CR engine. In reality it had 17cc dish pistons and 80cc heads that were supposed to be 76cc. The real CR was more like 6.77:1.
So your L-82 probably has more on the order of 7.5:1 to 8.0:1.
I purchased 64cc heads from Dart and they were in reality 67cc's. It's not as easy as you may be led to believe getting the CR up to something acceptable with just a top end.
So plan on using a cam that can support a lower compression ratio. The kit you mentioned may be ok for 9.5:1 at 6000 rpm but I bet it is a dog off the line. To me it looks like a cam for 10.5 or 11.0:1 CR. The RPM air gap intake is also a high rpm intake, not good for low end torque.
Do LOTS of homework before you pull the trigger. You'll be much happier with the results.

jb78L-82

A 77 L-48 advertised compression ratio for an L-48 is 8.5:1, not 8:1, just as a correction.

AirborneSilva

Thank you guys for all your comments, I do appreciate them. While I can put an engine together the math is not what I can do (yes I am a math moron!). I will abandon the idea of a "top end kit" and when the time comes I will look to you guys for help. I would like to get close to 400 HP out of the parts, cam, heads and intake. If I can only get 350 or so then that's what I get...

My current motor is a Jegs (GM), crate motor, they advertise it as 8.5:1 and I have a character flaw in that I tend to take people at their word The motor is advertised right now as 260 HP with the CR and 76 cc heads but whether any of that is actual I'm thinking your guess is better than mine.

Also, I currently have a 4 spd, will eventually put a 5 spd in it, with 355 gears.

Thanks again all