427 heads

[cobrabritt83]

does anybody know how many cc you can gain in your combustion chambers by going with a thicker head gasket.

[ERA Chas]

How much thicker than the standard .043 compressed?

[Danr55]

The volume of a cylinder is Pi X radius (squared) X height. convert Square inches to cubic centimeters by multiplying Sq. Inches by 64.516.

You should be able to get there from here.

[ERA Chas]

I get 5.5ccs with the piston down .010 in the hole and the .043 gasket*. The chamber would add 77+ccs to that. What other size gaskets are available and why do you want to lower compression?

*Assuming a 4.23 bore.

[FWB]

what heads are on it now?

[cobrabritt83]

it has 427 low riser heads with 72 cc chambers which will put me at 11.5:1

[ERA Chas]

That means the heads have been cut. I forgot how many ccs increase = 1 point of compression. Maybe the builders will jump in.
Maybe a CNC profile on the chambers is better than gaskets. Thay are cast chambers and have room for it. I don't know if thicker gaskets are available for FE.
Or better yet-improved, economical heads like Edelbrocks to lower compression.

[FWB]

Originally Posted by cobrabritt83

it has 427 low riser heads with 72 cc chambers which will put me at 11.5:1

yes i agree with chas, edelbrocks would put you at 78-80 out of the box. but you could like chas said machine your chambers, some valve unshrouding would probably do it

but the aluminum would be more forgiving in the compression dept.
you'd get better guides right away also with edel's

11.5 is too much for pump gas....at least for me....i like the 10.0 range

[bill37341]

You can decrease compression with a Cometic gasket. I used an .073 gasket to reduce my '27 medium riser to 10.3. Forgot the numbers on my heads, but my block had been cut slightly after being sleeved. The gaskets are expensive, but you can "customize" the compression with them. Good luck, Bill.

[blykins]

The typical Edelbrock head is 74cc out of the box. Pond heads are closer to 90.

I would not stack a big thick head gasket under the head just to decrease the compression ratio. If your piston is .xxx" in the hole and you stick a .060-.070" head gasket on it, then you butcher your quench distance.

I'm usually at 10-10.7:1 with aluminum heads and 93 octane. I've ran a tad over 11 without an issue.

If you're making a guess at what your compression ratio is, I would urge you to take some measurements so that you have a better handle on it.

[bobcowan]

Thick gaskets will lower your compression, but by such a small amount that it's really not worth it. Especially - as said above - when you kill your quench area.

Instead, you should consider changing your cam timing. Hold your intake valve open just a little bit longer and lower your dynamic/effective compression.

Dynamic CR

Interactive JavaScript to Calculate Engine's Compression Ratio (CR)

http://www.kb-silvolite.com/calc.php?action=comp2

[bill37341]

Britt- I have a 70 year old brain and 19 year project .Sometimes I forget a few things. Blykins and Bob are correct about quench distance. In my particular case, quench wasn't a problem, and thicker gaskets were the solution. My block had been cut before I got it, and then again when we sleeved it. My pistons were actually Proud of the block a few thousandths, and the gaskets helped me achieve a .050 or .060 quench distance. (Forgot how much.) If your engine is apart, measure the depth of the piston in the hole before you go to a thicker gasket.