GM CNC heads
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Intermediate
Joined: May 2006
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GM CNC heads
Does any one have experience with, or knolwedge of, the GMPP 88958665 CNC'd cylinder heads. These are the ones that GM performance sells, and that were used in the ASA and showroom stock classes. I have a new set and was wondering how they would work on a moderately modified LS2. I have talked with Ed at Lingenfelter, Andy at A&A, and J. Formato about this, and each has a differing opinion. The intake ports are large (245 - 250 cc), but they use the 2.00 inch LS6 valves. The consensis is that they are a decent middle of the road piece, as CNC heads go, but are most effective at higher rpm's.
I guess my concern would be that, with the large intake ports, they may tend to be soft (or dogs) in the low and mid-range. It dosent do much good for most of the power to be made up top (6000+rpm) in a street/touring motor. In the world of the traditional 23 degree motors, my experience is that anything much above 215 cc intake volume is for larger displacements, or a pretty seroius performance piece.
I guess my concern would be that, with the large intake ports, they may tend to be soft (or dogs) in the low and mid-range. It dosent do much good for most of the power to be made up top (6000+rpm) in a street/touring motor. In the world of the traditional 23 degree motors, my experience is that anything much above 215 cc intake volume is for larger displacements, or a pretty seroius performance piece.
Tech Contributor
Joined: Jul 2002
Posts: 14,950
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From: St. Louis, MO
St. Jude Donor '08
My buddy has them in a 98 C5 MN6 with a 230ish cam on a 115 LCA. With Dynatech headers w/cats he has 420 rwhp and 400 rwtq. I've driven his car - it is the most streetable H/C car I've seen (and I've had one and been around a bunch at our Corvette Challenge). He has a ton of low end torque and runs consistent 11.8's at 120 in our heat and has got 11.5x. I think these are excellent heads.
Give Mike Norris a call at Next Level performance and ask him what he thinks. He just tuned the car (tell him it's Mike C's black 98 C5 he tuned at Champion last Friday). I trust what Mike says, he doesn't steer people wrong and is THE expert around here.
Give Mike Norris a call at Next Level performance and ask him what he thinks. He just tuned the car (tell him it's Mike C's black 98 C5 he tuned at Champion last Friday). I trust what Mike says, he doesn't steer people wrong and is THE expert around here.
Last edited by Joe_G; Jul 26, 2006 at 09:43 PM.
Team Owner
Joined: Sep 2003
Posts: 43,084
Likes: 33
From: Raleigh / Rolesville NC
that is a good head for a LS6. For the LS2 the GM #88958622
is a better head. This the head the speed world challange corvettes use.
"Unbelievable performance from fully CNC ported cylinder heads. Some of the best low and mid-lift numbers we have ever seen from a stock size valve. These heads will flow over 200cfm at 0.300" lift and 290+ at 0.500". Fully assembled with the 2002 Z06 light-weight valves and the new '02 valve springs.
These heads have been milled 0.055" to bring the combustion chambers back down to approximately 60.9cc. Care must taken to check pushrod length and proper intake installation when using these cylinder heads. "
about 995 each
is a better head. This the head the speed world challange corvettes use.
"Unbelievable performance from fully CNC ported cylinder heads. Some of the best low and mid-lift numbers we have ever seen from a stock size valve. These heads will flow over 200cfm at 0.300" lift and 290+ at 0.500". Fully assembled with the 2002 Z06 light-weight valves and the new '02 valve springs.
These heads have been milled 0.055" to bring the combustion chambers back down to approximately 60.9cc. Care must taken to check pushrod length and proper intake installation when using these cylinder heads. "
about 995 each
Drifting
Joined: Jun 2005
Posts: 1,837
Likes: 4
Are these heads any different except for that 0.055 in?
Do you have any (better) data on compression ratios for these heads on the LS6 and LS2? I come up with the following, but it is based on some possibly inaccurate data and I'm just estimating the actual residual volume from the published numbers.
Given:
LS6 bore 99mm stroke 92mm
swept volume 708cm3 residual volume 9.5cm3
LS2 bore 101.6mm stroke 92mm
swept volume 746cm3 residual volume 11cm3
Then:
LS6 w/65.0 cm3 chamber (708+9.5+65.0)/(9.5+65.0) = 10.50
w/60.9 cm3 chamber (708+9.5+60.9)/(9.5+60.9) = 11.06
LS2 w/64.5 cm3 chamber (746+11+64.5)/(11+64.5) = 10.88
w/65.0 cm3 chamber (746+11+65.0)/(11+65.0) = 10.81
w/60.9 cm3 chamber (746+11+60.9)/(11+60.9) = 11.38
An 11.38:1 compression ratio seems pretty steep for 93 octane pump gas!
Also, GMPP has CNC'd LS2 heads, about $750. The difference is the valves, the LS2 heads have the solid valves instead of the hollow intakes and sodium-filled exhaust valves. But I'm not sure I wouldn't go the extra $250 for the lighter (and hopefully faster cooling) valves.
Do you have any (better) data on compression ratios for these heads on the LS6 and LS2? I come up with the following, but it is based on some possibly inaccurate data and I'm just estimating the actual residual volume from the published numbers.
Given:
LS6 bore 99mm stroke 92mm
swept volume 708cm3 residual volume 9.5cm3
LS2 bore 101.6mm stroke 92mm
swept volume 746cm3 residual volume 11cm3
Then:
LS6 w/65.0 cm3 chamber (708+9.5+65.0)/(9.5+65.0) = 10.50
w/60.9 cm3 chamber (708+9.5+60.9)/(9.5+60.9) = 11.06
LS2 w/64.5 cm3 chamber (746+11+64.5)/(11+64.5) = 10.88
w/65.0 cm3 chamber (746+11+65.0)/(11+65.0) = 10.81
w/60.9 cm3 chamber (746+11+60.9)/(11+60.9) = 11.38
An 11.38:1 compression ratio seems pretty steep for 93 octane pump gas!
Also, GMPP has CNC'd LS2 heads, about $750. The difference is the valves, the LS2 heads have the solid valves instead of the hollow intakes and sodium-filled exhaust valves. But I'm not sure I wouldn't go the extra $250 for the lighter (and hopefully faster cooling) valves.
Team Owner
Joined: Sep 2003
Posts: 43,084
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From: Raleigh / Rolesville NC
Originally Posted by revo1059
If GM heads are installed (let's assume by a GM dealer), is the warranty still intact if anything were to happen (if the failure was related to the heads)?
These heads are only warrentied do to manufacturing defects, ie no warrenty once installed would be my guess.
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Race Director
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From: Supporting the Corvette Community at Abel Chevrolet in Rio Vista, CA 707-374-6317 Ext.123
St. Jude Donor '08
I have them
I installed these on my Z06 and they are great. See sig for list of mods and H/P #'s
Race Director
Joined: Nov 2005
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From: Supporting the Corvette Community at Abel Chevrolet in Rio Vista, CA 707-374-6317 Ext.123
St. Jude Donor '08
Originally Posted by revo1059
If GM heads are installed (let's assume by a GM dealer), is the warranty still intact if anything were to happen (if the failure was related to the heads)?
Tech Contributor
Joined: Mar 2003
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From: Colorado Springs, CO
St. Jude Donor '08-'09-'10-'11
Originally Posted by Z11409
GM Performance heads are made by Edelbrock-always a good product.
Race Director
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From: Supporting the Corvette Community at Abel Chevrolet in Rio Vista, CA 707-374-6317 Ext.123
St. Jude Donor '08
Originally Posted by GN1270
I may be wrong, but I think he is asking if his power train warranty will be voided by GM if these heads are installed by a GM dealer, not if the part itself is warranted.