can I get some opinions? What kinda of hp/tq would a 243 headed lq9 make? The combo would consist of stock 243 heads, .051 mls gaskets, pro comp head studs, tsp 220/.581/112, pac1218's, comp 7.4's, cal speed long tubes ory. Stock injectors and throttle body and truck intake.

Going in the truck in my sig. Significant power over the 157,xxx mile tsp 220 cam'd 5.3?

Thanks

 

I believe the 243s are going to put you north of 11:1 on an lq9. As to the 5.3, and LQ9 is roughly 40ci bigger and the 243s/317s flow much better -- all else being equal, that's significantly better performance in can.

(That said, I'd do 317s... Same flow, same valves (unless you are sure the 243s are from a C5 zo6), 10.1:1 compression)

 

Whats the difference in a truck head 243 vs vette head 243? Just the sodium filled valves? And I'm guessing 11:1 is a bit extreme for a dd heavy 4x4 truck. Would it make 400whp with 317 heads?

 

10.9:1 is the spec if you get the same gasket thickness as an LS2....... because then you have an iron LS2. I think they are .054" compressed so maybe you will be bang on 11:1. Sodium filled valves that are lighter is the only difference beyond the obvious being springs. Truck 243's have stainless exhaust valves and steel intakes.

I would do 243's..... but that's just me, lol. LS2's make fine daily drivers.. As far as power goes.... I don't make guesses. Too many hurt feelings.

 

depends. if you already have 317s, mill them .030 and save money. same flow as 243s except difference is is in ccs. if you dont have heads, then yes get 243s. z06 243 heads have hollow stem intake valves and sodium filled exhaust valves. a lil rare and harder to find. hard to tell unless you weigh valves. milled 317s or regular 243s will do the trick. youll have much more torque and power for your truck and be happy. i would do a tbss/nnbs intake down the road.

 

The lq9 is a fresh short block. I like the fact of a 243 for the compression factor. I local machine shop has a set of 243's and will surface them for $450. I can probably have them put my springs and set up for $500. But then again I can get a set set of 317's for $200. Decisions decisions...

 

go with the 243 heads IMO youll get more compression which equals more torque

 

I too vote 243s. By the time you paid $200 for the 317s and had them milled to match the 243s 66 or 67ccchamber you'd be into more than the $450 they want for the 243s. Plus with 243s the intake will fit with no problems, with the milled 317s you could run into intake sealing issues.

 

Never even thought about the intake sealing after milling..

Would a non milled 243 use the same length pushrod as a milled .030 317? I know I'm gonna measure regardless which head I buy.

 

since you dont have heads yet buy the 243's. Sodium valves are nice but not worth the money IMO. id look for a regular 243 or 799 head and run em. Cheaper.

FYI milling them .030 you will not have sealing issues! the main issues anyone would face after milling would be PTV clearence. With a cam as small as that in a 6.0, you wouldnt have to worry about it at all. The bigger the cam the more you will have to worry about PTV. Iv heard mixed things about PR length with milled heads and not enough to make a definite answer. Only way to know is to use a pushrod checker. Thus being dependent on cam size, which lifter you use (ls7 is a tiny bit larger than stock lq9), and springs.

I myself am in the same boat, decision wise, as you are. Should i mill my 317's or buy 243's? is the compression worth the cost? Problem with milling is once its gone, your not getting it back.