mygiftmycurse

What would the compression be if i put factory 243 heads on an ls3 block?

Also, would the ls6 cam work well with that?

Anybody have a setup like that?

If you're curious, I'm wanting to build a budget motor with ls3 bare block and use parts from my ls6. I know there are other options, but I'd like advice on this at the moment. If it doesn't make sense, ill save for a better set-up.

chaase

I believe you can put LS6 heads on an LS3, but not vice versa. I do not know if it is good or bad though.

AU N EGL

Correct

There are several builders do taking off LS3 heads and putting on 243 heads onto an LS3 block.

less likely to have the oiling issues of the LS3 heads, under hard hard high G braking or hard high G left and sweeping corners.

mygiftmycurse

We've determined that they bolt up and should flow well enough for stock hp levels.
I'm still concerned about the compression ratio of the motor though.

chevylad

Isn't the LS3 head a rectangle port head? If that's true, the LS3 head is a bigger flowing head than the 243 head. I believe you lose about 5cc of head volume to increase compression, but you lose flow.

I would rather run the LS3 head and use an L76 manifold.

A.R. Shale Targa

In production form the 243 flows about 260 cfm and the LS3 is just
about 300. The thing that flow numbers don't show is port speed
(runner efficiency). The LS3 head at 265 cc of volume compared to 214
cc for the 243, has much less air velocity at low lifts and low rpms. Now
GM also put the LS3 heads on an engine with 30 more cubic inches;
but with an intake runner volume equal to the old big block oval ports,
they really seem to shine on 427 cid and larger engines. I'd bet you will
gain roughly 7/10s of a point of compression and a bunch more low/mid
range torque and throttle response since the 243 combustion chamber
is 64.45cc. I doubt the 01-04 LS6 cam is much if any larger than the LS
3, IIRC 204/218 .551/.547 117.5 ls. If you do make the switch I'd
consider trying to find a cam in the 224-230 duration range which will
bump another 40 or so rwhp while having stock like driving manners.

Z QQH 6

2010 L99 block in 2002 WS6 2003 LS6 243s with valve job
nice cam stock LS6 intake CAI headers 452 rwhp A4 compression 11:1 with stock head gasket.

mygiftmycurse

Excellent info. I read that the ls3 cam is identical on the intake side and very close on the exhaust side, compared to ls6 cam. I think I'll get with a vendor to choose a stronger cam. This should fit my needs well

AU N EGL

again the challenge with the LS3 heads is under hard High G braking Oil pools in the heads, or under high speed high G left hand sweeping corners, again oil pools in the heads.

and runs the bearings dry and BANG the engine blows. Only takes a sec or two and that is all she wrote.

and why some builders are going back to a ported polished 243 head for engine reliability.