How much can a L92 head be milled and/or what is the minimum chamber cc before it causes other physical fitment problems? It's about .005" mill per cc, correct?

 

 

I was told .006" per CC by BTR.

I know that you're asking specifically about gen iv stuff - which very likely may be different, but for other folks' reference, with cathedral stuff, .040 is the limit that you want to stay under. Things get very tight north of that.

 

Bringing this back from the dead, the same cylinder heads and pistons are still going strong after 2 seasons in a hillclimb/time trial car, so it doesn't get babied. Planning on going to a 12cc dome piston and different cam and intake manifold for next season.

Only fitment issue is the intake needs to be "pulled down" into place, but it fits with no leaks. Didn't check port alignment. Combo made 504/466 through garbage 1 5/8" headers on a dynojet on E85 26* timing at 12:1 AF (gas scale).

 

I have personally seen a AFR or TFS LS3 (cant remember which one) head milled .125. It cut into the bottom accessory bolt hole. Supposedly was for a LS3 SBE on E. My machinist told him it wasn't a good idea, but owner said do it. In general, milling any head more than .040-.050 is going to cause the some fitment problems. I think the plastic intakes are more forgiving of bad fitment, but I wonder how many are way off.