I have a set of TFS 23 degree heads being ported now. They already have the CNC chambers so they are rated at 64cc. The guy doing the work is going to clean up the chambers some more and do the 5 angle vale job and recess the valve into the head some. I was wondering since I am bolting these onto a stock ZZ4 bottom end if I should have the heads milled about .018 to get the compression back up maybe a bit more. According to TrickFlow .006=1cc so I would lose 3 cc in the chamber. I am already using the GMPP .028 thickness head gasket which with a 64cc heads should have given me around 10:1 compression. The guy porting the heads said its really not necessary since the porting will allow more air into the chamber and will actually increase my dynamic compression. I just think I would be better off having them milled. WOuld I run into any intake manifold sealing problems taking this much material off? I will be running a cam with 224/230 duration and .574/.577 lift with a 112lsa. Will I have any piston to valve clearance issues?

 

For what's it gonna cost you to have them milled, and no more power that will be had it's not cost effective at all. It's hard to say for sure if clearances will be okay, but that's a pretty small duration cam so it's not like the vales are hanging open for a long period of time throughout the piston movement, "my guess" is you'd be fine clearance wise milling the heads, but it's always in your best intrest to throw some playdough in the bore and run a full cycle to see what the real clearance acutally is. You may find you need to enlongate the intake bolt holes so they will start into the head and pull at the correct angle, we just delt with this last Fri night, buddy had heads milled and we had to enlongate holes in 4 spots to get them to thread in. intake was still fine on front/rear valley area.

you should also check valvetrain geometry also, it may require a shorter pushrod if using the same length valves.

There's not alot of power to be found with more compression, and using more compression really reflects back to the entire package your putting together.

 

So the guy doing the port work is right? Its not worth the bump back up in compression?

 

i have looked into this quite a bit

The compression with 64 cc heads and the zz4 shortblock would be around 9:1. If you plan on running a bigger cam you should definately consider getting your heads milled. If you mill them down to 58 cc, which is .036 in. then you will have about 10:1 compression which is a good number, expecially for aluminum heads which can take up to 11:1 with a bigger cam.

 

Was that 9:1 with what thickness head gasket? The Felpros are .041in and the GMPP are .028in thick.

 

That was just an extimate, probably with the fel-pro, the gmpp might be slightly higher than 9:1, maybe like 9.2:1 or so.

 

I milled my LT1 heads down to 48-49cc's for my 305. I will measure them later. Wtih felpro .015" gaskets, the LG4 should be running 10.3:1 with a XS262S solid lifter cam.

 

pellmanm I think you might have miss calculated:

SDPC Part Number: 12561723
Manufacturer: GM Performance Parts
Block : Cast Iron, 4- Bolt
Rear Seal : 1 - Piece
Crankshaft : Forged Steel
Stroke : 3.480"
Pistons : Hypereutectic 4VR Flat Top
Compression Ratio : 9.6:1 w/ 64cc heads
Compression Ratio : 8.8:1 w/ 76cc heads

 

Yes, you are correct on that, but i would still probably mill the heads down to 58 cc to get back the 10:1 compression that the zz4 has with the 58 cc H.O. aluminum heads.

 

yes I agree..I guess thats my next move

 

Just did a search and the zz4 crate engine is assembled with part number 12557236 head gasket which has a compressed thickness of .051in. With the 58cc heads this gives exactly 10:1 compression. MAybe I souldnt mill them all the way to 58cc???

 

That depends on your cam, bigger cams have more duration and overlap, which causes a loss in compression. Aluminum heads can take up to 11:1 compression.