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The build is a 6.2l from a lq4 block. I have a sloppy stage 2 cam .228 .230 .585 lift. I have 2 different set of heads. One is 317 heads milled at .20 or .25 and a set of 706 heads untouched. I have 2 questions. First which heads would make more hp and torque well just a better fit naturally aspirated with no boost. Second the 706 heads do not have the castech battery logo it has a different logo. Do anybody know is my 706 heads without the battery logo Castech heads or not. If I use the 706 heads I don't won't risk having issues with them. Somebody help please
Well the 317 head is 71.5cc and if I recall right you have to shave 7 thousands off you raise it by 1cc so if you have .25 shaved off you now have a 68cc
the 706 head has a 61cc chamber which is going to raise the compression BUT it is handicapped by a small intake valve 1.89 vs the 317 heads 2.00 intake valve
also the intake runner on the 706 is only 197cc while the 317 intake runner is 212cc
so what it boils down to is that the 317 is a better flowing head its vary similar to the 243/799 head many people run them on boosted applications and in your application is going to lower your compression ratio and the 706 is gonna flow like poo but raise your compression ratio at the end of the day if I was the one making the choice I would sell off the 317 head and buy a 243 then you don't have to worry about this situation and you may get lucky and get one with sodium valves
If you plan on spraying some n2o at the motor go with the 317 heads and run it but either way I would not run the 706
What pistons are now in the LQ4 is the big question? If they are non dished flattops with that overbore you're at least 10.5 static with non milled 317's. The factory LQ9 (flattops) with 317's are 10.2 static. I agree with the above post with the 243's but given the choice between the two sets of heads you have, depending on piston, I would chose the 317's for their better flow. I had the SS2 camshaft in LQ9 with stock 317's and that camshaft would easily turn to 6,800 rpm's. I think the 706's would do better with a smaller camshaft.
Not that big of a difference in flow. But I agree, if I was building this combo I would wanna start with a 799/243. or even better have the 706 heads ported and bigger valves installed.
Or go with a set of 823 heads
You didnt mention your budget or what the engine is going in
Subject been coved 1000x.
317 junk in a NA application
Huge chamber no squish velocity.
low compression. 706 9hp down to 799s.
compression is free power if u keep the same as before flow u had before milled
706 1d simulation. On a 6.0
same intake and cam as run by Richard .
what would happen if I lower compression and add some flow and change all the other things required to sim correctly with 317s
and yes i have 799 sim to. Same result as richard. There more to it than flows Flow curve from my bench used in sim
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6.2l lq4 
