243's vs. 317's
 

Aren't these heads very similar with different size combustion chambers? I don't see too many guys using the 317's, but I assume that the large combustion chambers are the reason. I have WCCH StageII 317's sitting on the shelf for my LQ9, which will be getting milled between .030-.040 when the time comes.

Here's a look at WCCH's StageII 317's flow data vs. their StageII 243 flow data:

http://www.proheads.com/WCCH%206.0L.html

http://www.proheads.com/WCCH%20LS6.html

The flow numbers are very close with the 317's actually flowing more until the lift gets up around .600, then the LS6's have a definite edge...

should be same flow, 72cc vs 65cc stock. 73.5cc would take ~ .040 mill to get to 68cc

what kinda CR are you shooting for?

About 10.6:1...Richard said that if I mill my 317's about .036 I should be right at my target cr with the flat topped LQ9.

I've done some research on them and supposedly the 243 will make more power.. With the same size combustion chamber.

I wonder why, as everything that I've heard says the ports are the same...something's gotta be different, as even WCCH's flow numbers are slightly better for the 243's once you get some healthy lift

I have wondered the same, ive like to get a nice set of 317s from a sponsor and run them without milling them, i bet it will surprise a lot of people, the only work i did on my 317s was milled .030, and i only gained .1 in the quarter and that was with the truck being 100lbs lighter. So what actually made my time drop? Milling the heads to bump up CR or the 100lbs? Im willing to bet it was the weight

i have the ported 317s milled to produce 10.6:1 on my lq9

I read somewhere (can't remember where or if its right) but that the combustion chamber was alittle different design than the 317s.. Supposedly a stock 317 with the same size combustion chamber as a 243 would come up about 20ft lb shorter on torque .. I can't remember where I read this info

Combustion chamber design makes sense with stock heads, but I wonder how different they could be once they're worked...