Thoughts on L92/LS3 vs Cathedral port for 8500rpm 408ci

General engine tech -- Drag Racing to Circle Track

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Shockwave
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Re: Thoughts on L92/LS3 vs Cathedral port for 8500rpm 408ci

Post by Shockwave » Sun Oct 15, 2017 5:40 pm

steve316 wrote:
Sun Oct 15, 2017 12:01 pm
What ever head you choose; I would not run them on a stock short block.Rods and pistons would have to be up graded at least. As far as witch head to run; I would vote for the ls3 because of air flow and the rocker arms you have. Ti valves will let your springs last 3 times longer. This is your budget so its your call, but if it comes a part it will not matter witch heads you have on, they most likely be scrap.Good luck Steve
Lol, no man, its just my DD Ls1 that has a stock bottom end somebody else asked about it earlier, thats where that comment came from.

The 408 rotating assembly is callies compstar crank/rods and wiseco pistons. This isnt a super budget build, im just not ready to lay out $4000 for heads for this build.

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Re: Thoughts on L92/LS3 vs Cathedral port for 8500rpm 408ci

Post by Shockwave » Sun Oct 15, 2017 5:42 pm

A_VAS wrote:
Sun Oct 15, 2017 11:28 am
i was suggesting putting a GM LS7 head on your 4.030 bore, not the "small bore" variants
if you have a take off that can be used to set on the block and take a look, I believe if you run a smaller exh valve it can be done.
I didnt know that was possible, I was under the impression you have to downsize both the intake and exhaust valve, which means installing new seats, and building up the bowl area with either weld or epoxy and re-porting for the smaller throat area, but I could be way off.

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Re: Thoughts on L92/LS3 vs Cathedral port for 8500rpm 408ci

Post by MadBill » Sun Oct 15, 2017 5:57 pm

Wonder if it would be possible to relieve the tops of the cylinders, a la BBC, far enough down to clear the valves at max lifts? :-k

Also, even in performance apps many stock valves substantially overhang their seats, so it might be possible to trim their ODs by 0.020" or more. The factory surely designed-in significant valve/bore clearance to cover off tolerance build up, which would help for a precision rework..
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Re: Thoughts on L92/LS3 vs Cathedral port for 8500rpm 408ci

Post by Shockwave » Sun Oct 15, 2017 7:08 pm

MadBill wrote:
Sun Oct 15, 2017 5:57 pm
Wonder if it would be possible to relieve the tops of the cylinders, a la BBC, far enough down to clear the valves at max lifts? :-k

Also, even in performance apps many stock valves substantially overhang their seats, so it might be possible to trim their ODs by 0.020" or more. The factory surely designed-in significant valve/bore clearance to cover off tolerance build up, which would help for a precision rework..
I dont know. I know the canted intake valve on the BBC helps that, angling towards the centerline if the bore, vs an inline valve that comes straight down into the cylinder wall. (Angled relief vs a straight cut)

Id have to look at the top ring land of the piston vs the deck and see how far towards the ring land it would come down.

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