I need some general info on a 420a Cylinder Head? A company I took my car to, to get the Engine replaced, and feel free to correct me if I am wrong, they took a factory Head and Deck it out at 40 over. If that is correct. Now if I'm correct Factory heads are decked at 20? Is it bad to put the car back together with it deck out that way or should I get a new head? Please help understand this. I know enough about the car just not that area.

Thanks

I believe for every .020 taken off of the head it bumps up your compression 0.5:1. So if they took .040 off you'll be a full 1.0:1 compression number higher and your gunna wanna look into getting adjustable cam gears to degree out your cams. When you take that much off of your head it messes with your timing geometry and you probably be a half of a tooth or more off on your cam gears.

Unless I'm wrong I thought the most the 420a cylinder head could be surfaced till the valves started getting too close to the piston at tdc was .040 - .042(even when timed correctly). When I was working at a engine rebuilding shop I did valve jobs and never heard of any head getting decked that much, let alone a 4 cylinder aluminum head. I wouldn't use it because any kind of warpage to your head would not be good, especially in your situation imo. The most I ever shaved off any type of cylinder head was mine at .021 and I did it to raise compression.