Ok so I bought a Cts v with the ls6 in it.
The guy who sold it to me said it has head work but he couldn't find the paperwork for it.
I did some looking around at the heads and it has 823 casting numbers. I understand these are heads for the ls3. From a few searches here is have also seen they don't work on the smaller bore in the ls6.

Well it seems to work fine. It's putting a confirmed 435 to the wheels with the stock cam. Only supporting mods are FAST lsxR 102 Fast fuel rails. FAST injectors. And the other usual bolt ons.

From what I understand I should actually lose power with these heads? Anyone help?

 

Its not an LS6 engine if it has those heads...its been replaced. 4" bore or larger only for those heads. And no, you wouldnt lose power with those heads, in stock form they outflow most cnc ported LS cathedral heads and make similar or more power than they do.

 

What year is the car? Later v's got the ls2 which has a 4" bore and will accept ls3 heads. 435 sounds pretty high also for that motor on the stock cam(if its actually stock). bolt on ls3's make that and they have more cubes, not only that but a cts0v is much less of a dyno queen than the cars ls3 motors come with

 

As in these heads shouldn't even bolt up to an ls6?

 

yaa.... they bolt up but the ls6 bore is 3.9. the heads need a 4" bore (ls2 size) to clear, otherwise the valves will try to occupy the same space as the cylinder walls, a problem which physics will correct pretty quickly

 

Try to figure out what block is in the car. Is it really a 5.7L LS6 or is it a 6.0L LS2?

If it is an LS2 block then it could have LS3 heads with standard valves.

If it is an LS6 block then it is most likely a small bore LS3 head with a smaller intake valve and intake valve seat installed. Look up the Ballistic Speed Parts small bore LS3 heads. Ballistic Speed has been out of business for a few years now though.

 

small bore ls3 heads are aftermarket castings and therefore wouldnt have an 823 casting number

 

Those heads could fit an LS6 block, they just have to be outfitted with much smaller valves than stock. But I somehow doubt you have an LS6 block in there as no way in heck would a small bore LS3 head make 435rwhp on the stock cam.

My bet, you have an LS3 block in there with 823 heads. Those have been known to make low 400s at the wheels with full bolt-ons.

Not necessarily, there have been shops taking stock 823 castings, replacing the valve seats to something smaller and then putting on 2.08 or similar valves. See the above example of BSP small bore LS3s.

 

Did not know that, but still the odds of that happening are very slim lol.

if the car had an ls3 he'd most likely have to have a conversion box in there for the reluctor wheel which I would think he would notice lol. I think its more likely the car has a tiny cam in it with the heads and is actually an early ls2 motor car

 

No, the Ballistic Speed small bores were 823 castings with 2.08" intake valves and valve seats.

 

yaa... redtan already corrected that

 

Could be a 24x LS3, but yeah I suppose it's more likely he has an LS2 with a small cam.