I have a zz4 350 that recieved from a friend that is going to go in my vette. The engine doesn't have the original cylinder heads, they are Edelbrock performer 6089. The original heads had 58cc combustion chambers the sbc 10:01compression while the edelbrocks has 64cc giving the sbc 9 to 9.5 compression I believe. What is the best way to raise compression, mill the heads or change the pistons? Milling would be easier and less expensive! To change pistons requires machine work, boring an honing which at this point might as well stoke it. Any would be much appreciated. Thanks.

Have the heads shaved down a little. Cheapest and easiest route. You will probably have to have the intake manifold shaved down to accommodate the angle change depending how much material is shaved off the heads.

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GEN III 5.7L "LS6" Engine swap
TKO500 5 spd.

I will have to look up what type of head gasket is used on a zz4, but the head gasket that I am going to use is a GM performance gasket that has a compression thickness of .028. I don't remember the part # off hand but it is in there performance catalog. I guess this will raise the compression by .5 I think.

Milling the heads also requires machine work...

The only machine work needed to swap pistons is pressing the pins out and back in. Honing would be optional, depending on how the cylinder walls look. The only reason you would need to bore the block would be if you went with an oversized piston, or the cylinder walls were severely worn...in which case raising the CR would be counterproductive.
Not sure simple gasket change would change the CR by .5, unless the original gaskets were really thick. By milling the heads, and using a quality, thinner gasket, you might get a .5 increase....depends a lot on how much is cut off the heads. You can only go so far before you have issues with the intake sealing properly, as Darryl mentions. The more the heads are cut, the farther away the intake ports are(wider) across the intake. This requires a thicker intake gasket, and milling of the bottom of the intake at the front and rear, where the end seal is. Get into angle milling, and you've opened a whole new can-o-werms.

Personally, I'd go with a piston swap....you can get a set of pistons that are designed to work with the chambers and valve sizes of the new heads, without all of the machine work involved in cutting the heads/intake. But that's just me.


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 Thanks for the info food for thought! I would have to measure the bore to see if in spec . If in spec I can replace the pistons. If not then full rebuild. If the later then I would go with a stroker kit because I think building a 355ci and a 383ci are close in price! with the 383 making more power. Am I correct thinking that way? I like to get  like 425 hp or more!

|UPDATED|11/18/2015 7:44:00 PM (AZT)|/UPDATED|

Good afternoon, You have an abundance of suggestion regarding trying to increase compression of you ZZ4 engine, all of which are good to very good,however if I may make a suggestion, and that is look into using steel gaskets and copper spray normally used to help seal the contact areas of the heads to block.

Brand:Fel-Pro

Manufacturer's Part Number:7733SH1

Part Type:Head Gaskets

Product Line:Fel-Pro Head Gaskets

Summit Racing Part Number:FEL-7733SH1

Bore (in):4.100 in.

Bore (mm):104.140mm

Gasket Material:Shim steel

Compressed Thickness (in):0.015 in.

Compressed Volume (cc):3.245cc

Lock Wire:No

Quantity:Sold individually.

In-Store Pickup:Choose In-store pick-up (OH, GA, NV) on our web site.

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