whats the difference between the #243 heads and the #317 heads? I read on here that the LQ4 heads and the LQ9 heads are the same so what makes the hp diff between the 2 motors?

 

The chamber size is different, 243 is I think 66cc the 317 is 72cc. They are supposed to flow very close to each other. The cams are different between the two motors also. I think the LS6 has sodium filled exhaust valves also.

 

So are 317 heads on LQ9 motors? And if the cams are diff and thats all I would like to know the cam specs of each.

 

yeah the LQ9 has the 317s, they are also on the LQ4. I am not sure about the cam specs, I had the LQ9 here somewhere but, I lost it. I believe that the LS6 would be a ZO6 cam.

 

So if i put the 243 heads on it should bump my CR up alittle bit? What is the stock CR on a LQ4?

Yeah i know the ls6 specs not to worried bout it i was told it would drop my tq level if i put that cam in. I was just concerned with the Z06's being the same as the LQ4&9's.

I am assuming another diff between the Z06 heads and LQ's besides the Combustion Chambers is the valve springs.

 

It would bump up the c/r a bit, not sure how much. Yes the springs would be different, I think the LS6 spring is yellow.

Stock c/r on the LQ4 I think is 9:5:1

 

The LS6 heads come with deifferent valves and springs, the valves are a different length due to different size of the camshaft base cicle. The springs are supposed to be good to about .550" lift.

 

317 Castings are 70cc untouched. 243 Castings are 64cc untouched. Note that ONLY the 243 heads that come off an 01-04 Z06 will have the snazzy valves and springs. Best springs are 02-04. 05 and 06 LS2's with the same head casting do not have the same valve part numbers. Can't remember regarding the springs. Just as a reference LS1 castings like the 241 are 66cc untouched. The 317 and 243 castings share the same intake and exhaust port design... with chamber design different to accomodate target CR and application. You can play with the calculator over at www.rosspistons.com/calculator and it will show you what happens when you start plugging in different chamber sizes, gasket thicknesses, etc. Using that calculator and ASSUMING you have a zero deck height, punching in the figures below, you can get an idea where you will wind up. I got 10.19:1 with the 70cc heads and 10.93:1 with the 64cc heads. The calculator is a good ballparking tool... but its always best to verify everything when swapping the heads... including checking lifter preload.

Bore = 4"
Stroke = 3.622"
Chamber size = 70cc (317) or 64cc (243)
Gasket Thickness = 0.054 (standard GM MLS gasket compressed)
Deck Height = 0 (assume zero - can't measure it unless you pull the heads)
Piston Dome/Dish = 0 (for flat top pistons)
Number of Cylinders = 8

What makes up the difference in horsepower is different compression ratio, intake manifolds, cams/springs, and exhaust flow capability.

Bill

 

The 2001+ LQ4 & LQ9 both have 317 heads. The CR is different due to the LQ4 having dished pistons and the LQ9 having flat top pistons. The cams are slightly different as well I believe.

 

LQ4 Stuff:

Cylinder Bore Size 4.00
Piston Stroke Length 3.62
Head Gasket Bore Diameter 4.04
Compressed Head Gasket Thickness .052
Combustion Chamber Volume In CCs 71.06
Piston Dome Volume In CCs Negative For Dished Pistons (Use '-') -8
Piston Deck Clearance Negative If ABOVE Deck (Use '-') -.006