Kbird

Long story short. I picked up an LT4 engine a couple of years ago for my 69 camaro. While the car is being painted I decided to install a different cam. Installed the cam and was taping it up for paint. I noticed on the heads a stamping "milled 0.017". The heads were also stamped for the specific side, LH and RH.
Should I be concerned that the heads were milled? Guess on compression ratio?
Engine had the LT4 intake, heads, crane gold rockers,.... The engine was installed in my camaro, started, and ran for a couple of minutes before removed.

Thanks,
Kevin

MTBSully

depends on how thick the head gaskets are.

andysc

Kevin

Need some more info before we can assist you. Like specs on the cam, lift, duration, etc. Next if the heads were off, you do not know if the pistons were changed also. Best bet would be to remove one head, put some clay on of one pistons that is at TDC, reinstall the head and rotate the engine at least two revolutions, then remove the head and measure the thickness of the compressed clay. You also do not know what springs are on the heads, and adding a larger cam may float the valves. You really need to find out all the specifics of the engine before proceeding.


HTH

Andy Schuck

Kbird

I didn't take the heads off. We had a warm day here in MI the other week. So, I took advantage of it. Installed the cam, etc. and painted the engine. The cam removed had BC 142 on the end of it. I installed the LT4 hot cam.

Kevin

SS RRR

.017 is really not that much. If you are that concerned, take the heads off and have them CC'd. That way you can get a very accurate measurement. It'd be a good excuse to install some fresh head gaskets.

Zaknafein

You can approximate. Knowing that every .006 milled (23º heads), decreases combustion chamber volume by 1cc... so you're looking at approximately -2.8cc. Punch that value into a static comp ratio calculator and go from there.

Obviously, the most accurate way is going to be as SS RRR mentioned... cc'ing the heads.

Kbird

Thanks for all the feedback. Before moving forward and installing it back into the car. I wanted to get an idea if I should be concerned that the compression ratio is excessive. If I remember correctly, most calibrators ask for the compression ratio.
Andy makes a good point about the valve springs. Should I change the valve springs out since I have gone with the LT4 Hot cam?

Thanks,
Kevin

Zaknafein

You should be more concerned with Dynamic compression than Static. Do search in the Advanced Tech forum for more information on the subject.

Yes, you should change the valvesprings. A call to Comp, K-motion, etc., should get you moving in the right direction.