Question about raising CR methods on LS7
Thread Starter
Staging Lane
Joined: Sep 2013
Posts: 58
Likes: 0
Question about raising CR methods on LS7 I have a C6Z and was planning my next round of upgrades.
I bought this car with most of the work already done to it and forgive me if these questions are stupid but I just want to learn more about my setup and CR in general.
My car's motor blew a while back from the previous owner and the following parts were installed to rebuild the motor
LS7 block
GM LS7 head gaskets
PSI LS1511ML valve springs
xceldine titanium retainers
ferrea exhaust valves
LS1 main stud kid
LS2 cam bolt kit
Mahle forged flat top piston set
head resurfacing/replace exhaust valves and seals
here are my cam specs
duration at .050 intake 240 exhaust 248
lobe lift intake .3430 exhaust .3400
gross valve lift intake .617 exhaust .612)
now here comes the actual question...
my CR is 12:2:1
Is it safe to assume what raised the compression ratio of the motor was the flat top pistons? I didn't see anything about thicker head gaskets or decking the block. I did however see the head resurfacing, could that also be taken as "milling" as well?
I want more power so I was thinking of a set of ported heads. Now I was told that very little power comes from the head porting and most of it comes from actually milling the head, with my compression ratio could I actually go higher? or should I just stick with strictly ported heads?
I was reading that depending on the cam size I could run a high compression and the cam may be able to bleed off some compression as well. With my cam specs is this the case?
Thanks for the help guys
I bought this car with most of the work already done to it and forgive me if these questions are stupid but I just want to learn more about my setup and CR in general.
My car's motor blew a while back from the previous owner and the following parts were installed to rebuild the motor
LS7 block
GM LS7 head gaskets
PSI LS1511ML valve springs
xceldine titanium retainers
ferrea exhaust valves
LS1 main stud kid
LS2 cam bolt kit
Mahle forged flat top piston set
head resurfacing/replace exhaust valves and seals
here are my cam specs
duration at .050 intake 240 exhaust 248
lobe lift intake .3430 exhaust .3400
gross valve lift intake .617 exhaust .612)
now here comes the actual question...
my CR is 12:2:1
Is it safe to assume what raised the compression ratio of the motor was the flat top pistons? I didn't see anything about thicker head gaskets or decking the block. I did however see the head resurfacing, could that also be taken as "milling" as well?
I want more power so I was thinking of a set of ported heads. Now I was told that very little power comes from the head porting and most of it comes from actually milling the head, with my compression ratio could I actually go higher? or should I just stick with strictly ported heads?
I was reading that depending on the cam size I could run a high compression and the cam may be able to bleed off some compression as well. With my cam specs is this the case?
Thanks for the help guys
Teching In
Joined: Dec 2005
Posts: 36
Likes: 0
Well if your on the stock LS7 head gaskets then the increase in compression could only come from either smaller reliefs in the new pistons (the stock ones have ~ 5cc reliefs) or a smaller combustion chamber (result of milling the heads).
Porting the heads can be worth some power (maybe 30?), an FAST intake and 102mm TB may be worth an additional 15. Do you already have long tube headers?
12.2:1 compression is already pretty high for pump gas. At this point I dont think more compression is a great way for you to pick up power.
Porting the heads can be worth some power (maybe 30?), an FAST intake and 102mm TB may be worth an additional 15. Do you already have long tube headers?
12.2:1 compression is already pretty high for pump gas. At this point I dont think more compression is a great way for you to pick up power.
I have a C6Z and was planning my next round of upgrades.
I bought this car with most of the work already done to it and forgive me if these questions are stupid but I just want to learn more about my setup and CR in general.
My car's motor blew a while back from the previous owner and the following parts were installed to rebuild the motor
LS7 block
GM LS7 head gaskets
PSI LS1511ML valve springs
xceldine titanium retainers
ferrea exhaust valves
LS1 main stud kid
LS2 cam bolt kit
Mahle forged flat top piston set
head resurfacing/replace exhaust valves and seals
here are my cam specs
duration at .050 intake 240 exhaust 248
lobe lift intake .3430 exhaust .3400
gross valve lift intake .617 exhaust .612)
now here comes the actual question...
my CR is 12:2:1
Is it safe to assume what raised the compression ratio of the motor was the flat top pistons? I didn't see anything about thicker head gaskets or decking the block. I did however see the head resurfacing, could that also be taken as "milling" as well?
I want more power so I was thinking of a set of ported heads. Now I was told that very little power comes from the head porting and most of it comes from actually milling the head, with my compression ratio could I actually go higher? or should I just stick with strictly ported heads?
I was reading that depending on the cam size I could run a high compression and the cam may be able to bleed off some compression as well. With my cam specs is this the case?
Thanks for the help guys
I bought this car with most of the work already done to it and forgive me if these questions are stupid but I just want to learn more about my setup and CR in general.
My car's motor blew a while back from the previous owner and the following parts were installed to rebuild the motor
LS7 block
GM LS7 head gaskets
PSI LS1511ML valve springs
xceldine titanium retainers
ferrea exhaust valves
LS1 main stud kid
LS2 cam bolt kit
Mahle forged flat top piston set
head resurfacing/replace exhaust valves and seals
here are my cam specs
duration at .050 intake 240 exhaust 248
lobe lift intake .3430 exhaust .3400
gross valve lift intake .617 exhaust .612)
now here comes the actual question...
my CR is 12:2:1
Is it safe to assume what raised the compression ratio of the motor was the flat top pistons? I didn't see anything about thicker head gaskets or decking the block. I did however see the head resurfacing, could that also be taken as "milling" as well?
I want more power so I was thinking of a set of ported heads. Now I was told that very little power comes from the head porting and most of it comes from actually milling the head, with my compression ratio could I actually go higher? or should I just stick with strictly ported heads?
I was reading that depending on the cam size I could run a high compression and the cam may be able to bleed off some compression as well. With my cam specs is this the case?
Thanks for the help guys
Thread Starter
Staging Lane
Joined: Sep 2013
Posts: 58
Likes: 0
Well if your on the stock LS7 head gaskets then the increase in compression could only come from either smaller reliefs in the new pistons (the stock ones have ~ 5cc reliefs) or a smaller combustion chamber (result of milling the heads).
Porting the heads can be worth some power (maybe 30?), an FAST intake and 102mm TB may be worth an additional 15. Do you already have long tube headers?
12.2:1 compression is already pretty high for pump gas. At this point I dont think more compression is a great way for you to pick up power.
Porting the heads can be worth some power (maybe 30?), an FAST intake and 102mm TB may be worth an additional 15. Do you already have long tube headers?
12.2:1 compression is already pretty high for pump gas. At this point I dont think more compression is a great way for you to pick up power.
I just picked up the FAST intake and NW 102MM TB. I also have longtube headers and Catless Xpipe.
any ideas what the highest compression I can run safely is? or am I already there?
Registered User
Joined: May 2014
Posts: 34
Likes: 0
As far as static compression goes, I would keep it where you're at ( 12.2 ) Dynamic compression ( engine running / operating ) is separate and has to do with cam lobe center line separation and valve opening / closing points. I've seen DCR's in the high 8's, very low 9's range, on pump 93 btw.
You'd have to get complete cam / lobe specs, head gasket thickness, head chamber cc's to figure out DCR.
As far as power gained by porting the heads, to an extent, more of the power gained typically come from milling the heads vs. porting them, but who ports them has a lot to do with the power gained as well.
To give you a better idea of where to look for additional power, what does the rest of your engine combo consist of ( induction / exhaust )?
You'd have to get complete cam / lobe specs, head gasket thickness, head chamber cc's to figure out DCR.
As far as power gained by porting the heads, to an extent, more of the power gained typically come from milling the heads vs. porting them, but who ports them has a lot to do with the power gained as well.
To give you a better idea of where to look for additional power, what does the rest of your engine combo consist of ( induction / exhaust )?
Registered User
Joined: May 2014
Posts: 34
Likes: 0
DCR is an area where it's possible for you to gain a little bit of power. A Reputable port job on the FAST 102 is another area, leave the TB alone.
As far as porting the heads goes, I would seriously look into Frankenstein Racing Heads, then Darin Morgan @ Reher-Morrison.
KP Racing recently build a heads, cam, exhaust, stock intake, stock tb, stock cold air intake C6Z that pushed a almost, or just a tad over 600RWHP with FRH head work!!!
I want more power so I was thinking of a set of ported heads. Now I was told that very little power comes from the head porting and most of it comes from actually milling the head, with my compression ratio could I actually go higher? or should I just stick with strictly ported heads?
A full point in compression is worth 3% extra power, so say 15-18rwhp. And that's alot of milling to do, so more realistically you can gain 10rwhp from milling the heads. However porting them can gain 40-50rwhp.
Registered User
Joined: May 2014
Posts: 34
Likes: 0
It's actually the opposite. Most of the power is gained from the ported heads and a little bit from the milling.
A full point in compression is worth 3% extra power, so say 15-18rwhp. And that's alot of milling to do, so more realistically you can gain 10rwhp from milling the heads. However porting them can gain 40-50rwhp.
A full point in compression is worth 3% extra power, so say 15-18rwhp. And that's alot of milling to do, so more realistically you can gain 10rwhp from milling the heads. However porting them can gain 40-50rwhp.
So, in the LS7's case, typically, more power is gained by milling the heads vs. porting the heads. Again, every combo is, and can be, different when it comes to results, so the key word here is, Average / typical.
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Staging Lane
Joined: Sep 2013
Posts: 58
Likes: 0
As far as static compression goes, I would keep it where you're at ( 12.2 ) Dynamic compression ( engine running / operating ) is separate and has to do with cam lobe center line separation and valve opening / closing points. I've seen DCR's in the high 8's, very low 9's range, on pump 93 btw.
You'd have to get complete cam / lobe specs, head gasket thickness, head chamber cc's to figure out DCR.
As far as power gained by porting the heads, to an extent, more of the power gained typically come from milling the heads vs. porting them, but who ports them has a lot to do with the power gained as well.
To give you a better idea of where to look for additional power, what does the rest of your engine combo consist of ( induction / exhaust )?
You'd have to get complete cam / lobe specs, head gasket thickness, head chamber cc's to figure out DCR.
As far as power gained by porting the heads, to an extent, more of the power gained typically come from milling the heads vs. porting them, but who ports them has a lot to do with the power gained as well.
To give you a better idea of where to look for additional power, what does the rest of your engine combo consist of ( induction / exhaust )?
the FAST102 is ported and I also have a NW 102mm TB and cam specs are above