LS3 heads on LS2 Engine
Thread Starter
Racer
Joined: Aug 2016
Posts: 354
Likes: 54
LS3 heads on LS2 Engine
I am in the process of adding LS3 heads, intake, and BTR cam to a factory LS2 engine. I would like to retain the factory compression ratio.
LS2 heads have 64cc chambers
My LS3 heads have 68.5cc chambers
To retain the factory static compression ratio of 10.9:1, I will need to mill the heads. Does anyone know the exact amount that needs to be milled from the heads to achieve a 64cc chamber in the LS3 heads?
Additionally, the lift of the replacement cam is a concern leading to PTV contact concerns with milled heads.
Considering two different cams:
226/231 113+4 0.605"/0.598"
230/235 114+4 0.609"/0.610"
I believe these cams would be considered quite small for this combo. Will I have issues with PTV clearance concerns with either of the above cams?
Thank you for the schooling in advance.
LS2 heads have 64cc chambers
My LS3 heads have 68.5cc chambers
To retain the factory static compression ratio of 10.9:1, I will need to mill the heads. Does anyone know the exact amount that needs to be milled from the heads to achieve a 64cc chamber in the LS3 heads?
Additionally, the lift of the replacement cam is a concern leading to PTV contact concerns with milled heads.
Considering two different cams:
226/231 113+4 0.605"/0.598"
230/235 114+4 0.609"/0.610"
I believe these cams would be considered quite small for this combo. Will I have issues with PTV clearance concerns with either of the above cams?
Thank you for the schooling in advance.
Drifting
Joined: Nov 2009
Posts: 1,385
Likes: 102
General rule of thumb is every .006 off the heads is 1cc. I would do this instead...mill the heads .02 and THEN go with a cometic .040 gasket the thinner gasket will help raise compression without hacking more off the head and it will also bring down quench which will help fight off detonation. Combined those 2 things will put you just a smidgenover the stock compression ratio.
As always you should check ptv clearance when screwing with milling and such
As always you should check ptv clearance when screwing with milling and such
Last edited by redbird555; Oct 14, 2016 at 11:22 AM.
Thread Starter
Racer
Joined: Aug 2016
Posts: 354
Likes: 54
General rule of thumb is every .006 off the heads is 1cc. I would do this instead...mill the heads .02 and THEN go with a cometic .040 gasket the thinner gasket will help raise compression without hacking more off the head and it will also bring down quench which will help fight off detonation. Combined those 2 things will put you just a smidgenover the stock compression ratio.
Are you saying that I will gain ~0.6scr (to ~11.0:1) by milling the heads 0.020" to reduce the combustion chamber volume by 3.3cc (drops LS3 heads to 65.2cc) and the reduced thickness Cometic head gasket will reduce by another 3cc?
Or how much will the Cometic 0.040" thick gasket gain? What is stock thickness head gasket?
I may be willing to drop the compression ratio to a bit by just doing a thinner head gasket. Does Cometic make thinner than 0.040" thick head gasket?
Drifting
Joined: Nov 2009
Posts: 1,385
Likes: 102
Yes give or take mulling the heads .02 and running the thinner gasket will put you right around 11.1:1 which is absolutely no problem with pump gas. I recommend keeping the compression up there as compression will also help fuel economy as well as drive ability.
The stock gasket is .054 compressed and the cometic will be .040 this allows the head to be closer to the block creating a better compressed fuel mix which will decrease the chance of getting small hotspots on the piston which normally causes pre detonation.cometic does make a thinner head gasket but you have to be careful going too thin will increase the likelihood of not getting a good deal between the head and block. Another issue with this is that on ls engines the piston sticks up out of the block a.004-.006 so bringing the head too close to the block with a really thin gasket may cause the piston to smack the bottom of the head. On a stock short block ls .040 is a good safe number to be at with the HG
The stock gasket is .054 compressed and the cometic will be .040 this allows the head to be closer to the block creating a better compressed fuel mix which will decrease the chance of getting small hotspots on the piston which normally causes pre detonation.cometic does make a thinner head gasket but you have to be careful going too thin will increase the likelihood of not getting a good deal between the head and block. Another issue with this is that on ls engines the piston sticks up out of the block a.004-.006 so bringing the head too close to the block with a really thin gasket may cause the piston to smack the bottom of the head. On a stock short block ls .040 is a good safe number to be at with the HG
