Anyone know the specs on these heads??? LINK Think they might be from the L33s?

 

I think they come on the all aluminum 5.3L motors in the SSR, Trailblazer, and other cars. Not sure on the specs if they are altered for compression, deck height, etc.
First guess is that they are similar to the 862 castings and have the smaller intake valve for the smaller 5.3L bore.

 

valves are 1.87/1.57 on theses heads. same chamber and runner size as 241 Ls1 castings.

 

Unless I missed something, the 241 heads were only equipped with 2.00"/1.55" valve sizes.
I'll check with my sources on the 421 head specs and try to shed some light on this subject.

Richard

 

You are probably right, the smaller valves are due to the smaller bore size of the 5.3L motor. I will say the dreaded "valve shield" term now and expect a bunch of naysayers to chime in.