"317" LS-based head work, anyone game?

[Xnke]

So I am still working this welded-together hybrid, all the bores are aligned correctly and the deck has been full-face welded to increase deck thickness and chamber volume slightly. Hope to hit a 76ish CC chamber, for the most part the welded-face will be machined almost completely away. More chamber volume will NOT hurt me, as 76cc is going to be the minimum size I can use with inexpensive, off-the-shelf forged pistons. Any smaller on the chamber and I have to start getting into very big dish volumes in the piston. (4.040" bore, 3.98" stroke)

I have been intending to port this welded-together head at home, and have had good luck with the exhaust sides. My flow bench may not have enough scrote to pull the higher depressions that porters seem to want to see on the LS-6 ports, and the CNC game is out as so far, no one wants to touch the 6-chamber head. (Must set reference on one chamber and the automation does the rest? I'd say that isn't a great method, and I'd prefer it centered up on each chamber correctly, but what do I know?)

So, guys who have worked with the LQ4/LQ6 317 casting, I am planning to fit ~2.1" intake valves, 1.6" exhausts, and am wary of the port work. CSA already seems slightly large, but doesn't seem to be hurting anyone, and most go bigger yet on the 400" V-8 engines. Where am I going to get into trouble with the larger valve? I have *read* that removing the rocker boss causes the port to "back up", and that the "swirl ramp" is only there to keep the SSR of the port loaded when the valve lift gets over a certain point...how much of this is truth and how much of this is crap spread by the internet? I mention 400" V-8 engines because my 300" 6-cylinder will have equivalent per-cylinder flow requirements.

Given that I can move the side of the chamber over 0.050" away from the intake valve, I don't see a big shrouding *increase* coming from the 0.050" bigger valve radius. I've got room for the bigger valve, and it won't cost any more to get one in there over a stock diameter, as I need to change the seats anyway after welding the head. How big of a valve can the port support? Keep in mind the intake manifold will be essentially a tunnel-ram style, 7" long straight tubular runner, max runner ID currently possible 2.5".

This head will be getting a slightly tighter 4-bolt pattern than the LS bolt pattern, with 1/2" ARP studs and a quality headgasket. The welding will increase deck thickness to about 0.600", and I will be running 16-20lbs of boost through the engine, turbocharged.

Anyone still hand-port these castings? If so, I may consider farming the head work out...it pains me to do so but it's cheaper to do it right the first time.

[powellmachine]

i am in the process of testing port work, flow verses hp, as we speak, so for I have seen positive results from the normal bowl and seat work, the port itself seems to b touchy, ls3/l92's are not, just a note 2.02 seems like a good # unless we are increasing port volume significantly, imo. I have picked up 30 cfm across the board with basic port work. there is more in the head tho.

[Kenova]

I have never ported a head but I would sure like to see a picture or two of your little project.

Ken

[In-Tech]

I just mentioned(in another post) the great work I've received on multiple sets of LS heads from Richard.

Check them out.

http://proheads.com/

[needforspeed66gt]

I'm pretty sure you can't even fit a LS3 valve package into those heads without moving the guides over, they're offset in those heads for a reason. Plus, with your 4.04" bore size it ends up quite shrouded and a 2.02"/1.60 valve package has no issue moving enough air for that engine especially if you're shoving air into it.

[Orr89rocz]

I thought the 317 was identical to the 243 for port shape and just had different chambers. Why couldnt a cnc for a 243 not work for a 317? I've seen 317 ported heads offered from several suppliers, advanced induction, prc, tea, etc

[In-Tech]

I thought the 317 was identical to the 243 for port shape and just had different chambers. Why couldnt a cnc for a 243 not work for a 317? I've seen 317 ported heads offered from several suppliers, advanced induction, prc, tea, etc

It basically is, whether his will work in a particular cnc fixture is the rub

[Xnke]

Yup, that's the issue. I have six chambers on a 4.489 bore spacing, and the head bolt pattern and distance from the deck to the valve seats has been altered. someone could set up and manually start and stop the CNC program to run each chamber individually, if the fixture was long enough, but most won't.

[user-612937456]

pictures please