they put 243s on 5.3s from factory. a 243 only flows 250 i think

 

that head for a larger bore also has 2.00" valves that you plan on using and they also flow more (in cast form) than the stock 5.3's.

 

LS6 have 3.905 bore, but the valve spacing is the same as a 5.3 head. The larger valve diameter (2.00") combined with the smaller 3.78" bore is what causes the shrouding effect. Same thing would happen when you put a 2.00" valve in a 5.3 head. Milling a head also can negativly affect flow slightly by placing the valve closer to the cylinder.

 

but the heads came on 5.3s from factory so it isnt as bad as you think

 

yeah but dont the L33 5.3 have flat top pistons so the head wasnt milled to up compression they just went with a flat/domed piston instead? That would be why there is no direct hit on the flow because the valve distance hasnt moved like Tdrumm is getting at.

 

not sure at all. I know the LS4 and the 5.3 truck motor runs them and those are the HO motors i beleive

 

I think you can get some dart heads for fairly cheap now. You might check on a set of those.

 

patriot performance sells a nice combo..

cnc'd 243 heads with chamber sizes to your liking with prc duel springs and titanium retainers for 1090.

 

Are you sure that they are 243s? Patriot used to market a "LS6 style" head that was a 317 head that they had weled up the chamber to get the volume down. Also, 2.00" is the max intake valve I'd run on a 5.3, and I'd be willing to bet that those heads have 2.02s and use larger port volumes to get their flow numbers, which could affect low speed torque.

 

they use 243 castings now. they just havent updated the website. its under new products on their current website.