Arw these the correct heads?
Le Mans Master
Joined: Dec 2004
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From: West coast CA
https://www.summitracing.com/parts/nal-12675871
The LS3 head p/n has lower-volume combustion chambers and hollow-stem intake valves.
Thread Starter
Melting Slicks
Joined: Nov 2011
Posts: 3,187
Likes: 266
From: Virginia
As it says in the description, p/n 12711770 is an L92 cylinder head. The LS3 head is p/n 12675871:
https://www.summitracing.com/parts/nal-12675871
The LS3 head p/n has lower-volume combustion chambers and hollow-stem intake valves.
https://www.summitracing.com/parts/nal-12675871
The LS3 head p/n has lower-volume combustion chambers and hollow-stem intake valves.
Thread Starter
Melting Slicks
Joined: Nov 2011
Posts: 3,187
Likes: 266
From: Virginia
So are the 12675871 heads a good replacement head? The only difference that I can tell apart from the stock head is maybe the valves have a two angle cut instead of a three angle cut like the 821’s. Other than that they seem identical. Are these inferior in any way?
Le Mans Master
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Thread Starter
Melting Slicks
Joined: Nov 2011
Posts: 3,187
Likes: 266
From: Virginia
I know it comes with the hollow intake valves but on the exhaust valves they might be heavier than the stock 821 exhaust valve. But no the car won’t ever see past 6500 RPM
Le Mans Master
Joined: Jul 2010
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Le Mans Master
Joined: Dec 2004
Posts: 5,492
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From: West coast CA
If you buy an LS3 crate motor (19540155), it comes with two 12675871 heads installed. The same heads also come on the LS376/480, LS376/515, LS376/525, DR525 and 525RLB crate motors.
The current "stock replacement solid-stem [exhaust] valve used in L92 and LS3 engines" is part number 12582719, which is the same as it was back during C6 production. It's the same valve. I presume this still-current "stock replacement" valve is what GM installs in their current 12675871 "stock LS3" heads.
Maybe there's a subtle difference between the LS3 replacement parts GM sells today and what they put in the Corvette originally, but I have no evidence that they're a lower-performance design. Some people have argued that QC isn't as good, but that's a separate problem.
Last edited by torquetube; Nov 29, 2024 at 11:19 PM.
Thread Starter
Melting Slicks
Joined: Nov 2011
Posts: 3,187
Likes: 266
From: Virginia
As it says in the description, p/n 12711770 is an L92 cylinder head. The LS3 head is p/n 12675871:
https://www.summitracing.com/parts/nal-12675871
The LS3 head p/n has lower-volume combustion chambers and hollow-stem intake valves.
https://www.summitracing.com/parts/nal-12675871
The LS3 head p/n has lower-volume combustion chambers and hollow-stem intake valves.
heads from a Chevy dealer using my vin and the heads that came are the L92 heads that I posted the picture of. I have some hollow intake valves so that’s not a problem but why kind of difference with the combustion volume difference make? I think it’s 70cc on these L92 heads and 68.4 on the other heads.
Safety Car
Joined: May 2016
Posts: 4,669
Likes: 1,849
From: Erlanger, Kentucky
So I ended up having a buddy order me some
heads from a Chevy dealer using my vin and the heads that came are the L92 heads that I posted the picture of. I have some hollow intake valves so that’s not a problem but why kind of difference with the combustion volume difference make? I think it’s 70cc on these L92 heads and 68.4 on the other heads.
heads from a Chevy dealer using my vin and the heads that came are the L92 heads that I posted the picture of. I have some hollow intake valves so that’s not a problem but why kind of difference with the combustion volume difference make? I think it’s 70cc on these L92 heads and 68.4 on the other heads.
Thread Starter
Melting Slicks
Joined: Nov 2011
Posts: 3,187
Likes: 266
From: Virginia
I will lower your static compression ratio a little. From an online calculator, it is showing a 0.2 lower compression ratio. Not really much. And you can make that back up with a thinner head gasket. 0.045 Cometic would do get it back to normal and give more squish which is a good thing.
Safety Car
Joined: May 2016
Posts: 4,669
Likes: 1,849
From: Erlanger, Kentucky
Great thanks for the info buddy. I have no idea why they sent the L92 heads because supposedly they used my VIN and that was the part number it pulled. I know these heads will work fine it just sucks because I did have to spend extra money to get the hollow intake valves. I know the solid ones would have worked like we discussed but for valvetrain stability purposes I went ahead and got the hollow valves. I also read that these heads don’t flow quite as good But I’m sure the difference is minimal if any different at all. I had already ordered both head gaskets and went with the factory replacements but I’m sure I can return those. If not, any idea how much that .2 lower compression ratio would actually affect hp/tq?
Thread Starter
Melting Slicks
Joined: Nov 2011
Posts: 3,187
Likes: 266
From: Virginia
It won't be much. Probably 1-3 hp, 5 at most. Nothing that would really make a difference. And might be able to run slightly more timing which would make up that difference. But the little bit thinner head gasket can make up for that. The thinner gasket would also have a better squish/quench. That has several benefits such as better resistance to detonation.
I hope I don’t end up regretting changing over to the cam motion Titan 2. I know cam motion makes great cams and has a great reputation and the Titan series is supposed to be really good but what makes me nervous is nobody seems to be using that cam from what I’ve seen. And I did call Cam motion to see about getting a custom grind but when I told them what I was looking for they suggested going with the Titan 2.
Safety Car
Joined: May 2016
Posts: 4,669
Likes: 1,849
From: Erlanger, Kentucky
Yeah makes sense, thanks for that info. Using a thinner head gasket might put me a little on the high side as far as lifter preload on these Johnson lifters but I’ll have to measure since I’m changing the cam. Also my current heads have had a valve job done and I know that can affect your lifter preload also, so who knows what length I’ll end up needing.
I hope I don’t end up regretting changing over to the cam motion Titan 2. I know cam motion makes great cams and has a great reputation and the Titan series is supposed to be really good but what makes me nervous is nobody seems to be using that cam from what I’ve seen. And I did call Cam motion to see about getting a custom grind but when I told them what I was looking for they suggested going with the Titan 2.
I hope I don’t end up regretting changing over to the cam motion Titan 2. I know cam motion makes great cams and has a great reputation and the Titan series is supposed to be really good but what makes me nervous is nobody seems to be using that cam from what I’ve seen. And I did call Cam motion to see about getting a custom grind but when I told them what I was looking for they suggested going with the Titan 2.
I take a more conservative approach to cams. And that is why my go-to for cam recommendations is CamMotion. The lift on their cams for the application is much more reasonable and realistic.
But people see big lift numbers and think it must be better. Duration has a much greater effect on power.
And with a 6.2L liter engine you are getting diminishing returns going with crazy lift and duration and and putting much more stress on components than is necessary. Fine for a race car but not a daily driver, street fun car. As an example, Cam Motion's LS7 Stage 1 cam has nearly the same duration and lift as Texas Speeds LS3 Stage 1 cam. The duration and lift numbers are appropriate for an LS7 but not an LS3; bigger displacement needs more lift and duration.
Last edited by Spaceme1117; Dec 28, 2024 at 12:18 PM.
Thread Starter
Melting Slicks
Joined: Nov 2011
Posts: 3,187
Likes: 266
From: Virginia
Don't worry, the Titan 2 will be awesome. And easier on the valve train. I like some of BTR's stuff; I'm running their shaft rocker system in my car. But I think they (and other cam makers) have way too much lift on some of their cams.
I take a more conservative approach to cams. And that is why my go-to for cam recommendations is CamMotion. The lift on their cams for the application is much more reasonable and realistic.
But people see big lift numbers and think it must be better. Duration has a much greater effect on power.
And with a 6.2L liter engine you are getting diminishing returns going with crazy lift and duration and and putting much more stress on components than is necessary. Fine for a race car but not a daily driver, street fun car. As an example, Cam Motion's LS7 Stage 1 cam has nearly the same duration and lift as Texas Speeds LS3 Stage 1 cam. The duration and lift numbers are appropriate for an LS7 but not an LS3; bigger displacement needs more lift and duration.
I take a more conservative approach to cams. And that is why my go-to for cam recommendations is CamMotion. The lift on their cams for the application is much more reasonable and realistic.
But people see big lift numbers and think it must be better. Duration has a much greater effect on power.
And with a 6.2L liter engine you are getting diminishing returns going with crazy lift and duration and and putting much more stress on components than is necessary. Fine for a race car but not a daily driver, street fun car. As an example, Cam Motion's LS7 Stage 1 cam has nearly the same duration and lift as Texas Speeds LS3 Stage 1 cam. The duration and lift numbers are appropriate for an LS7 but not an LS3; bigger displacement needs more lift and duration.
Safety Car
Joined: May 2016
Posts: 4,669
Likes: 1,849
From: Erlanger, Kentucky
Looking forward to you having it installed and running great.
