LS2 with LS3 Top end
Thread Starter
Instructor
Joined: May 2023
Posts: 217
Likes: 95
LS2 with LS3 Top end
I've been doing a lot of research on going with an LS3 top-end but would like some advice. I can get the heads locally and they advise me to stick with the 823 instead of the 821 since they claim the light weight valves are more prone to fail? I don't mind sacrificing a little hp for longevity.
Here is what they offer:
"I could have you a pair all done up, that’s with a fresh valve job, resurfacing bead blasting, new intake valves, resurfaced and bead blasted original gm exhaust valves and the btr .660 titanium retainer spring kit"
Now what I'm not sure about is what kind of compression will I end up with if I tell them to mill the head and by how much? I see most people with this setup running .040 head gaskets but what kind of compression will that get me exactly since the LS2 has more compression than an LS3 from factory.
I'm also worried about valve-to-piston clearance. I am told I should have room for 240* @.050 range but I really don't want to go too aggressive on the cam since I plan on supercharging down the road. Once I supercharge it, I would lower the compression but for now, I am looking to have as much as possible.
Lastly for the electrical portion. I plan on getting a complete LS3 intake manifold with injectors and fuel rails and use my silver blade LS2 90mm throttle body. Is an LS3 MAP sensor with an adapter harness all I need? I also plan on getting a harness to use a card style MAF.
Here is what they offer:
"I could have you a pair all done up, that’s with a fresh valve job, resurfacing bead blasting, new intake valves, resurfaced and bead blasted original gm exhaust valves and the btr .660 titanium retainer spring kit"
Now what I'm not sure about is what kind of compression will I end up with if I tell them to mill the head and by how much? I see most people with this setup running .040 head gaskets but what kind of compression will that get me exactly since the LS2 has more compression than an LS3 from factory.
I'm also worried about valve-to-piston clearance. I am told I should have room for 240* @.050 range but I really don't want to go too aggressive on the cam since I plan on supercharging down the road. Once I supercharge it, I would lower the compression but for now, I am looking to have as much as possible.
Lastly for the electrical portion. I plan on getting a complete LS3 intake manifold with injectors and fuel rails and use my silver blade LS2 90mm throttle body. Is an LS3 MAP sensor with an adapter harness all I need? I also plan on getting a harness to use a card style MAF.
8th Gear
Joined: Mar 2025
Posts: 8
Likes: 1
I've been doing a lot of research on going with an LS3 top-end but would like some advice. I can get the heads locally and they advise me to stick with the 823 instead of the 821 since they claim the light weight valves are more prone to fail? I don't mind sacrificing a little hp for longevity.
Here is what they offer:
"I could have you a pair all done up, that’s with a fresh valve job, resurfacing bead blasting, new intake valves, resurfaced and bead blasted original gm exhaust valves and the btr .660 titanium retainer spring kit"
Now what I'm not sure about is what kind of compression will I end up with if I tell them to mill the head and by how much? I see most people with this setup running .040 head gaskets but what kind of compression will that get me exactly since the LS2 has more compression than an LS3 from factory.
I'm also worried about valve-to-piston clearance. I am told I should have room for 240* @.050 range but I really don't want to go too aggressive on the cam since I plan on supercharging down the road. Once I supercharge it, I would lower the compression but for now, I am looking to have as much as possible.
Lastly for the electrical portion. I plan on getting a complete LS3 intake manifold with injectors and fuel rails and use my silver blade LS2 90mm throttle body. Is an LS3 MAP sensor with an adapter harness all I need? I also plan on getting a harness to use a card style MAF.
Here is what they offer:
"I could have you a pair all done up, that’s with a fresh valve job, resurfacing bead blasting, new intake valves, resurfaced and bead blasted original gm exhaust valves and the btr .660 titanium retainer spring kit"
Now what I'm not sure about is what kind of compression will I end up with if I tell them to mill the head and by how much? I see most people with this setup running .040 head gaskets but what kind of compression will that get me exactly since the LS2 has more compression than an LS3 from factory.
I'm also worried about valve-to-piston clearance. I am told I should have room for 240* @.050 range but I really don't want to go too aggressive on the cam since I plan on supercharging down the road. Once I supercharge it, I would lower the compression but for now, I am looking to have as much as possible.
Lastly for the electrical portion. I plan on getting a complete LS3 intake manifold with injectors and fuel rails and use my silver blade LS2 90mm throttle body. Is an LS3 MAP sensor with an adapter harness all I need? I also plan on getting a harness to use a card style MAF.
Safety Car
Joined: May 2016
Posts: 4,667
Likes: 1,849
From: Erlanger, Kentucky
I've been doing a lot of research on going with an LS3 top-end but would like some advice. I can get the heads locally and they advise me to stick with the 823 instead of the 821 since they claim the light weight valves are more prone to fail? I don't mind sacrificing a little hp for longevity.
Here is what they offer:
"I could have you a pair all done up, that’s with a fresh valve job, resurfacing bead blasting, new intake valves, resurfaced and bead blasted original gm exhaust valves and the btr .660 titanium retainer spring kit"
Now what I'm not sure about is what kind of compression will I end up with if I tell them to mill the head and by how much? I see most people with this setup running .040 head gaskets but what kind of compression will that get me exactly since the LS2 has more compression than an LS3 from factory.
I'm also worried about valve-to-piston clearance. I am told I should have room for 240* @.050 range but I really don't want to go too aggressive on the cam since I plan on supercharging down the road. Once I supercharge it, I would lower the compression but for now, I am looking to have as much as possible.
Lastly for the electrical portion. I plan on getting a complete LS3 intake manifold with injectors and fuel rails and use my silver blade LS2 90mm throttle body. Is an LS3 MAP sensor with an adapter harness all I need? I also plan on getting a harness to use a card style MAF.
Here is what they offer:
"I could have you a pair all done up, that’s with a fresh valve job, resurfacing bead blasting, new intake valves, resurfaced and bead blasted original gm exhaust valves and the btr .660 titanium retainer spring kit"
Now what I'm not sure about is what kind of compression will I end up with if I tell them to mill the head and by how much? I see most people with this setup running .040 head gaskets but what kind of compression will that get me exactly since the LS2 has more compression than an LS3 from factory.
I'm also worried about valve-to-piston clearance. I am told I should have room for 240* @.050 range but I really don't want to go too aggressive on the cam since I plan on supercharging down the road. Once I supercharge it, I would lower the compression but for now, I am looking to have as much as possible.
Lastly for the electrical portion. I plan on getting a complete LS3 intake manifold with injectors and fuel rails and use my silver blade LS2 90mm throttle body. Is an LS3 MAP sensor with an adapter harness all I need? I also plan on getting a harness to use a card style MAF.
I would NOT have the heads shaved any as you want to lower the compression especially if you will be supercharging. LS2 is already a bit on the high side with a 10.9 CR. Going to an LS3 top end should lower it to about 10.7.
LS3 821 heads have 69cc combustion chambers. 823 heads 70cc. Either would work fine. 823 heads would lower CR a little more than the 821's.
And I would choose an appropriate cam. If you will be supercharging, get a cam for that application. You can run it perfectly fine until you supercharge.
What is the application for the car? Race car, weekend drag strip, street strip, fun car/daily driver? And is the car an auto or manual?
Le Mans Master
Joined: Dec 2005
Posts: 6,999
Likes: 1,685
From: Southeast TX
I wouldn't fool with the heads if you know you're going to supercharge it. That's assuming it's not a max effort build. Going from 65cc to 70cc heads on an LS2 is going to lower your static CR below 10.3:1. While that "might" be beneficial if you're trying to run a bunch of boost, it's not beneficial on a mildly boosted street machine. Milling LS3 heads enough to get your static CR back to stock LS2 levels is going to cause PTV issues. To do it right, you'd need to fly cut your pistons.
I'd look for a cam with intake duration in the mid 220's, exhaust duration in the mid 230's, with a 115 or 116LSA. Lift in the low .600's. Good power potential without many, if any, big cam demons.
I'd look for a cam with intake duration in the mid 220's, exhaust duration in the mid 230's, with a 115 or 116LSA. Lift in the low .600's. Good power potential without many, if any, big cam demons.
Safety Car
Joined: Apr 2007
Posts: 4,461
Likes: 326
From: Houston TX
I didn't think anyone still explored these conversions since the price/performance isn't nearly as attractive as it used to be. I think if you plan to supercharge, just put your pennies away for that and don't bother with any LS3 parts at all. I think these days you could get a set of used ported LS2 heads and FAST or MSD Atomic for not too much that would be a more direct swap with similar, if not better, gains.
Thread Starter
Instructor
Joined: May 2023
Posts: 217
Likes: 95
Honestly the price is what's making me hold back. Seeing supercharged LS2s with stock heads making well over 600hp is making me rethink things. I don't plan on making more than 600-700hp in the long run, I just don't want to regret not going with the better heads to start off with. A fast 102 manifold isn't much more than a complete LS3 manifold, I'm in Canada so everything costs more.
I think I will just get the 102 to pair with my 1 7/8 long tubes, change my valve springs with a mild cam and save the rest for the supercharger.
I think I will just get the 102 to pair with my 1 7/8 long tubes, change my valve springs with a mild cam and save the rest for the supercharger.
Drifting
Joined: Apr 2005
Posts: 1,917
Likes: 451
From: Central NJ
Honestly the price is what's making me hold back. Seeing supercharged LS2s with stock heads making well over 600hp is making me rethink things. I don't plan on making more than 600-700hp in the long run, I just don't want to regret not going with the better heads to start off with. A fast 102 manifold isn't much more than a complete LS3 manifold, I'm in Canada so everything costs more.
I think I will just get the 102 to pair with my 1 7/8 long tubes, change my valve springs with a mild cam and save the rest for the supercharger.
I think I will just get the 102 to pair with my 1 7/8 long tubes, change my valve springs with a mild cam and save the rest for the supercharger.
My Ls2 made 580 whp (A6) with just a set of shorty headers and an electric water pump.
Just seems like you're taking the long way around jmo
You have the long tubes already? -so less than 5k US but either way I'd go straight to supercharger and see where you're at and go from there, again jmo based on your hp goals.
