I'm doin the usual swap on the 5.3l for boost swapping in 317 heads... Now ,would ?I run with valve issues if I milled the heads .20 and use an aftermarket headsgasket cometic instead using .51 thick ill go with .30 thick. My reason of doing this is to keep the CP up ,keep hearing to prevent blowing off the head gasket to run a thin gasket..

 

Why use 317s if your just gonna mill them and use thinner gaskets ?
The only reason 317s are widely used on boosted engines, is to lower the compression ratio due to their larger 72cc chambers.

find an online compression ratio calculator and run the numbers for your engine spec's and see what you come up with.

The 317 heads require a 4" bore gasket to seal properly, the most popular available for boosted applications are the LS9 gaskets and are around .050"
compressed thickness.

 

I would not use the 317 heads on a 5.3. I used them for 2 years and low end torque suffered badly with the lower compression. I my opinion you really wont benefit from it unless you plan to run 20+ psi. The trade off isn't worth it . If its a track only setup with a trans brake then I guess it really doesn't matter.
Just my opinion from my experience with them. I have run 15 psi with the 862 heads with zero problems. No inter-cooler just E85.

 

^ Ya what they say. Dont do it....no point really....and it makes it a turd.

 

What would be ideal CR for a boosted 5.3? Say, using a single 76mm turbo?