Well, I'm probably wrong then. But for some reason I had it stuck in my mind that the intake valves are bigger on the 317's vs the 5.3 799 heads. I also remember Richard from WCCH recommending reworked 5.3 heads for the smaller bore engines vs 243's or 317's. But that was a few years ago.

Either way, I personally would never choose 317's for this application. Even if you mill the crap out of these heads to get the chamber smaller, you end up with thinner decks on the heads (bad for high boost), potential intake manifold alignment issues, and potential piston to valve clearance issues(on big cams).

Andy, how much boost are you planning with this build? Also, remember that your cam was spec'd for a lot more cubes, with a 10:1 SCR, and square port heads. IMO, completely wrong for what it seems like you have planned. I'm pretty sure you'd be very disappointed in the end.

 

If you mill the heads the decks will be thinner and more likely to lift.

 

The piston deck clearance should be negative. Most LS engine are about -0.006 or -0.007 on average (piston comes out of the hole). Also, -2cc valve reliefs is not the normal pistons used in 5.3 motors.

 

I don't know if this is high jacking a thread but- I'm milled .035 on 862 heads and running 8-9 psi and it runs great!!!
I also have thought about running 317 or 243 heads and have not came up with much research on it. Kind of curious myself on this topic. I was told if it makes more power n/a it will make more power boosted. But it all comes down to your setup. I was going for a n/a setup and was "finished" with my build until I came across this blower. I'm running a tr220 which is not the best boost cam.

However I want to run more boost on my mp122hh but I don't know if it's safe for my compression ratio-

 

I don't even know where to start on all this... The 243's on 5.3's currently have the same 2.0" 1.55" valves. The older 5.3's had a 1.94" intake valve. But a 2.0" intake valve will not be shrouded enough to hurt power especially on a boosted motor. On a set of WCCH heads there would likely be a 2.02 or bigger valve. Shrounding only really shows up as a problem on NA motors. But i agree that it would need 20+ lbs of boost to make the same power that could be had with a better head and compression ratio.

 

I think the 706 and 862 heads have 1.89" intake valves actually.

 

Yup thats what I thought too.

Andy why wouldnt you just run a 243 or 799? I doubt you have the flat tops in that 5.3, so it would lower your compression a little, but not nearly as drastically as the 317's would.

They may land you closer to where you want to be. Although I'm not sure I'd go all that much lower than stock as roger mentioned in his first post.

 

Sorry your right, I was think old school SBC...

 

I heard from a few people that the 317's would be a good option and like I mentioned they were free so wasn't so concerned if I didn't end up using them since it was no cost to me.


I have been focusing on paying some things off and other bills that I haven't even touched the truck this winter

Will keep the stock heads on there for now. Will sell the cam I have and get one speced for my blower and whatever size Yank stall I end up going with (will do the 4l80 swap). Still have my dual springs and hardened push rods, debating if I want to get roller rockers. Still have the rockers for my old truck, might sell those and pick up some LS1 style for this truck.

Dunno how much boost I will start off with, figure around low teens. Will do head studs and new gasket when I do the cam swap. Throw a NNBS intake and other supporting fuel mods and such.

I just really need to sit down and see everything I have, what I need and make up a plan. Will get a hold of Pat and have him help me spec out a cam for my goals. I would like to see something in the low 12's high 11's as a start.