CNC cathedral or LS3
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From: Fredonia,WI
CNC cathedral or LS3 Gonna be putting my 4.021" bore 368 inch LS2 into my vette here in the next few months. Have a 226/232 @ 114 camshaft and some Wagner 228cc ported 799 casting heads which supposedly flow 297 @ .600 with the 2.00" intake valve
Factory LS6 intake and self modded throttle body
Buddy of mine offered me some 0821 casting heads off his 12' GS vette with less than a thousand miles in them since new. He's trying to get me to go with his LS3 intake/throttle body on my short block.
I checked and the chambers measured 4.060" so about .020" shrouding will be the case on my engine.
My pistons are at zero deck so a .040" Cometic puts my squeeze at 10.8 without milling. Down about a half point from my current heads at 62cc with the much cheaper LS2 gaskets
Thoughts on if I should stay the plan with my 3.42 geared M6 car or consider running the LS3 top on my LS2 short block and whether or not I should also change the camshaft even though I would DIY port the 821 exhaust side
I'm only shooting for around 440 rear wheel but want near stock drivability with occasional 1/4 mile blasts. Mostly cruising type driving.
Comments welcome
Factory LS6 intake and self modded throttle body
Buddy of mine offered me some 0821 casting heads off his 12' GS vette with less than a thousand miles in them since new. He's trying to get me to go with his LS3 intake/throttle body on my short block.
I checked and the chambers measured 4.060" so about .020" shrouding will be the case on my engine.
My pistons are at zero deck so a .040" Cometic puts my squeeze at 10.8 without milling. Down about a half point from my current heads at 62cc with the much cheaper LS2 gaskets
Thoughts on if I should stay the plan with my 3.42 geared M6 car or consider running the LS3 top on my LS2 short block and whether or not I should also change the camshaft even though I would DIY port the 821 exhaust side
I'm only shooting for around 440 rear wheel but want near stock drivability with occasional 1/4 mile blasts. Mostly cruising type driving.
Comments welcome
Last edited by A.R. Shale Targa; Mar 23, 2016 at 12:56 AM.
Mostly cruising type driving.
If it was more than just a mild street cruiser I'd say LS3s with a new cam for sure, but those heads will perform better on the street with the smaller runners and higher compression.
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From: Wilmington, De
That cam would work fine with the LS3s. Milling the heads and using factory gaskets, you'd be around 11:1 without issue, and I'd bet that you would hit the high 400s without issue and with perfect street manners.
However, if you already have the 799 heads and don't plan on buying a new throttle body to bolt to the LS3 intake, then I would just keep what you have.
However, if you already have the 799 heads and don't plan on buying a new throttle body to bolt to the LS3 intake, then I would just keep what you have.
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From: Fredonia,WI
The buddy of mine kept his injectors/rails so I'd end up needing to find some.
My cathedral combo will most likely need some FAST36 injectors to meet my target power level.
I'll probably end up staying the plan as my short block and heads are all together and I'm happy with all the clearances.
For me the temptation comes from the intake and TB being better and the heads having such few miles on them, practically new.
He also has his original LS3 block/rods/Pistons/rings which he pulled at around 2K
I just can't justify starting over with his stuff for eight more cubic inches.
I'm thinking you guys have convinced me that I've picked the appropriate combination for the intended usage I have for my car
Thanks again 👍
My cathedral combo will most likely need some FAST36 injectors to meet my target power level.
I'll probably end up staying the plan as my short block and heads are all together and I'm happy with all the clearances.
For me the temptation comes from the intake and TB being better and the heads having such few miles on them, practically new.
He also has his original LS3 block/rods/Pistons/rings which he pulled at around 2K
I just can't justify starting over with his stuff for eight more cubic inches.
I'm thinking you guys have convinced me that I've picked the appropriate combination for the intended usage I have for my car
Thanks again 👍
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Keep the cathedrals. There have been some who have made around 500rwhp on LS2's with ported 799's so you have plenty of head flow for ~450rwhp. The smaller chambers will also be more responsive on the street.
Jason
Jason
If this was a matter of stock 799 cathedrals vs stock LS3's and we were talking about port velocity id be inclined to agree with the latter, but since we are talking about CNC'ing the cathedrals vs LS3 heads, don't bother wasting the money hogging out the 799's to achieve LS3 type flow when you can just swap the LS3 heads on and LS3 intake for cheaper. Port velocity is always hurt on the cathedral heads no matter how you CNC them, it's just a matter to what degree. There is nothing about the LS3 heads that are going to make your car less "streetable".
don't bother wasting the money hogging out the 799's to achieve LS3 type flow when you can just swap the LS3 heads on and LS3 intake for cheaper.
There is nothing about the LS3 heads that are going to make your car less "streetable".
There's more to a set of heads than just flow. And if you do want to use flow as a benchmark, look at the size of the heads for the given flow. Those ported cathedrals with something like 22x cc runner flow the same as an LS3 with a 260 cc runner...not exactly impressive.
No it won't make a car less streetable with LS3 heads sure. But a car with small port high velocity heads flowing the same as some monstrous rectangular heads will drive a helluva lot better and snappier on the street.
No it won't make a car less streetable with LS3 heads sure. But a car with small port high velocity heads flowing the same as some monstrous rectangular heads will drive a helluva lot better and snappier on the street.
There's more to a set of heads than just flow. And if you do want to use flow as a benchmark, look at the size of the heads for the given flow. Those ported cathedrals with something like 22x cc runner flow the same as an LS3 with a 260 cc runner...not exactly impressive.
No it won't make a car less streetable with LS3 heads sure. But a car with small port high velocity heads flowing the same as some monstrous rectangular heads will drive a helluva lot better and snappier on the street.
No it won't make a car less streetable with LS3 heads sure. But a car with small port high velocity heads flowing the same as some monstrous rectangular heads will drive a helluva lot better and snappier on the street.
hogging a cathedral port head out to make it the same size as an LS3 head port is pointless when you can do the LS3 conversion for less money
you would need a 232cc CNC ported cathedral head to match the flow rates of an LS3 head and would have LESS port velocity then the stock LS3 head would have making the CNC ported cathedral heads worse in terms of low rpm streetability.
How do you explain that?
It's not just the port size, but a 2.16" intake valve will make a big difference in airspeed compared to the 2" on a ported cathedral head.
PTV clearance is also much less on the LS3 head with it being the same 15 degree valve angle. Your cam may not be large enough to pose an issue, but you certainly won't have as much cushion in the event of an over rev or if the valve springs begin to weaken over time.
Jason
PTV clearance is also much less on the LS3 head with it being the same 15 degree valve angle. Your cam may not be large enough to pose an issue, but you certainly won't have as much cushion in the event of an over rev or if the valve springs begin to weaken over time.
Jason
Really? Then what did you mean by this:
Highly debatable.
That's not what we're talking about. YOU stated a 232cc cathedral port would have less "velocity" than a stock 260cc rectangle port. That's the statement I am calling BS.
No they're not.
No they're not.
Keep the cathedral ports reasonable and you can get the peak power you want with great torque. The LS3 heads are good for more power stock and they won't have the port flow you want to keep a broad torque motor. I like the cam specs I've seen. What lift is it?