Cometic head gasket lowers compression?
03-18-2003, 11:58 AM
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Cometic head gasket lowers compression? What is the standard thickness for a LS1 head gasket - .060?
I purchased ported heads that have been milled .055.
Does Cometic supply gaskets that are .095 thickness? Who sells these?
...I want to run a naturally aspirated setup with a big cam and I beleive the stock gasket will result in piston/head clearance issues with the .055 milled heads.
I purchased ported heads that have been milled .055.
Does Cometic supply gaskets that are .095 thickness? Who sells these?
...I want to run a naturally aspirated setup with a big cam and I beleive the stock gasket will result in piston/head clearance issues with the .055 milled heads.
03-18-2003, 07:21 PM
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Re: Cometic head gasket lowers compression? I do run a .078 Cometic gasket which is the Max I think stock non-milled heads should run.
I think you should consider selling the heads and purchasing the right setup for Forced Induction. That's too much compression to address with gaskets.
I think you should consider selling the heads and purchasing the right setup for Forced Induction. That's too much compression to address with gaskets.
03-19-2003, 07:24 AM
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Re: Cometic head gasket lowers compression? OK great; but I'm NOT planning to run forced induction...just straight motor! ...The naturally aspirated guys said the forced induction guys run thick gaskets to kill compression....this is th eonly reasoin why I am here...
Is .078 the thickest gasket Cometics makes? ...their web page has stock .060 gaskets only....
Is .078 the thickest gasket Cometics makes? ...their web page has stock .060 gaskets only....
03-19-2003, 07:49 AM
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Re: Cometic head gasket lowers compression? You might be able to have the stock pistons cut while the heads are off for the PTV issues. Dunno if that can be done.
Cometic makes a .098 or so, but I don't recc it.
Cometic makes a .098 or so, but I don't recc it.
03-19-2003, 08:51 AM
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Re: Cometic head gasket lowers compression? ...so you beleive anything over .078 thinckness in a non-blower car will result in a blown head gasket or other bad stuff?
....I suppose the other choice would be to run a lower lift cam ....i don't want to fly-cut the pistons ...especially while the motor is in the car...besides ...i have not purchased the cam yet only the .055 milled Lingfelter ported heads. By the way, SDPC sells 60 sets of these heads per month ...so i am surprised this gasket/clearance issue is not more common.
Where did you buy your THICK Cometic head gaskets?
Thax,,,
....I suppose the other choice would be to run a lower lift cam ....i don't want to fly-cut the pistons ...especially while the motor is in the car...besides ...i have not purchased the cam yet only the .055 milled Lingfelter ported heads. By the way, SDPC sells 60 sets of these heads per month ...so i am surprised this gasket/clearance issue is not more common.
Where did you buy your THICK Cometic head gaskets?
Thax,,,
03-20-2003, 02:41 PM
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Re: Cometic head gasket lowers compression? ...good question! ...I surveyed the normally aspirated guys to see if anyone had the same .055 milled head and .560 lift cam combination.
Only one person replied. He said his intake valve was real close (clay measured) but he was running fly-cut stock pistons....so he basically said I need to address the situation before I get to the wrenching part of the install...
Only one person replied. He said his intake valve was real close (clay measured) but he was running fly-cut stock pistons....so he basically said I need to address the situation before I get to the wrenching part of the install...
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03-20-2003, 02:47 PM
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Re: Cometic head gasket lowers compression? ...someone above suggested that the proper way to do it would be to open up the combustion chamber...
Since opening up the combustion chamber will successfully lower compression ratio but it does nothing to relieve the piston/valve clearence issue, I assume this is a bad (dumb?) resonse...
Thanks anyway...
Since opening up the combustion chamber will successfully lower compression ratio but it does nothing to relieve the piston/valve clearence issue, I assume this is a bad (dumb?) resonse...
Thanks anyway...
03-20-2003, 08:30 PM
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Re: Cometic head gasket lowers compression? If valve to piston clearance is your only issue get some pistons with valve notches. They are usually only 2cc so your CR will not drop too much.
How big of CAM do you plan on running? What size valves are in the heads & what kind of valve springs are you using?
I had Katech run my heads on there dyno that measures valve bounce, and with 1.60" intake valves, a 230 duration CAM & Rev 1116 dual springs the bounce was 0.020" to 0.035" at 6200RPM, which in your case would hit your pistons.
How big of CAM do you plan on running? What size valves are in the heads & what kind of valve springs are you using?
I had Katech run my heads on there dyno that measures valve bounce, and with 1.60" intake valves, a 230 duration CAM & Rev 1116 dual springs the bounce was 0.020" to 0.035" at 6200RPM, which in your case would hit your pistons.
03-21-2003, 12:30 AM
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Re: Cometic head gasket lowers compression? Going with a thicker head gasket will be detrimental to the performance of the engine. The squish band area requires minimal clearance at TDC to obtain proper combustion. The proper way would be to open up the combustion chamber or dish the pistons.
03-21-2003, 12:34 AM
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Re: Cometic head gasket lowers compression? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by robertbartsch:
<strong>i have not purchased the cam yet only the .055 milled Lingfelter ported heads. By the way, SDPC sells 60 sets of these heads per month ...so i am surprised this gasket/clearance issue is not more common.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">So, Question...
What exactly makes you think that you'll have V-to-P clearance issues if you don't have the heads on the car right now?
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<strong>i have not purchased the cam yet only the .055 milled Lingfelter ported heads. By the way, SDPC sells 60 sets of these heads per month ...so i am surprised this gasket/clearance issue is not more common.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">So, Question...
What exactly makes you think that you'll have V-to-P clearance issues if you don't have the heads on the car right now?
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03-21-2003, 05:10 AM
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Re: Cometic head gasket lowers compression? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by robertbartsch:
<strong>Since opening up the combustion chamber will successfully lower compression ratio but it does nothing to relieve the piston/valve clearence issue, I assume this is a bad (dumb?) resonse...</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif"><img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />
If you really want to know about your P-to-V, then use your stock gaskets, which you have now, and bolt on one head with the intended cam installed. Put some modeling clay on the piston and rotate the assembly 720 degrees. Cut away the area that is thinnest and measure.
Remember that the cumulative distances of lift and head milling, etc, aren't really the entire picture. The duration is what holds the valves out toward the piston; the piston chases the exhaust valve, the intake chases the piston, so even the degree to which you advance or retard the cam can make or break the P-to-V clearance.
Once you know the relative clearance then, knowing the stock gasket thickness, you can make an informed decision as to whether a thicker gasket is in order.
Oh... and don't sweat the "valve bounce". If you keep .080" on the intake and .100" on the exhaust, you'll never have a problem. Bounce is only a concern if your trying to push the tolerance stack, which is something better left to racers and people with more money than sense (or little of either). I ran a mechanical roller with staggering lift rates and at .080/.100 I never had any problem at 8000rpm, even with true flat-tops.
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<small>[ March 21, 2003, 10:49 AM: Message edited by: SS00Blue ]</small>
<strong>Since opening up the combustion chamber will successfully lower compression ratio but it does nothing to relieve the piston/valve clearence issue, I assume this is a bad (dumb?) resonse...</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif"><img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />
If you really want to know about your P-to-V, then use your stock gaskets, which you have now, and bolt on one head with the intended cam installed. Put some modeling clay on the piston and rotate the assembly 720 degrees. Cut away the area that is thinnest and measure.
Remember that the cumulative distances of lift and head milling, etc, aren't really the entire picture. The duration is what holds the valves out toward the piston; the piston chases the exhaust valve, the intake chases the piston, so even the degree to which you advance or retard the cam can make or break the P-to-V clearance.
Once you know the relative clearance then, knowing the stock gasket thickness, you can make an informed decision as to whether a thicker gasket is in order.
Oh... and don't sweat the "valve bounce". If you keep .080" on the intake and .100" on the exhaust, you'll never have a problem. Bounce is only a concern if your trying to push the tolerance stack, which is something better left to racers and people with more money than sense (or little of either). I ran a mechanical roller with staggering lift rates and at .080/.100 I never had any problem at 8000rpm, even with true flat-tops.
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<small>[ March 21, 2003, 10:49 AM: Message edited by: SS00Blue ]</small>
03-21-2003, 07:29 PM
#13
Re: Cometic head gasket lowers compression? If you want to be cheap about it, get some playdoh and stick about a fist size amount in your C.C. and torque your heads down (with the old head gasket of course).. Crank the engine over BY HAND, make sure your ignition and fuel are disconnected... This will show you your P-T-V clearance.. You can then cut playdoh in half and measure the clearance and use it to position or reference how much you want to cut out of your pistons..
Going with a thicker head gasket will just run you the chances or constantly replacing head gaskets and re-milling your heads every time they blow...
Your best bet is to do it right and buy the right heads.. If you want I have some stock LS1 heads that im currently porting.. If you interested PM me..
Going with a thicker head gasket will just run you the chances or constantly replacing head gaskets and re-milling your heads every time they blow...
Your best bet is to do it right and buy the right heads.. If you want I have some stock LS1 heads that im currently porting.. If you interested PM me..
03-21-2003, 11:25 PM
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Re: Cometic head gasket lowers compression? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by jpas:
<strong> Going with a thicker head gasket will be detrimental to the performance of the engine. The squish band area requires minimal clearance at TDC to obtain proper combustion. The proper way would be to open up the combustion chamber or dish the pistons. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Yeah like the ones I have <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
<img src="http://james.jaguar.net/kctrading/Pics-of-truck-3-2-02/383-Shortblock/closeup-srp-pistons.jpg" alt=" - " />
31cc dish forged SRP's I run mod vortec steel heads right now that have been milled (57cc chambers) with .008 engine deck height and a felpro .039 gasket to get 9 to 1 comp but I'm running 10psi of intercooled boost on a 383 engine <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
Ken
<strong> Going with a thicker head gasket will be detrimental to the performance of the engine. The squish band area requires minimal clearance at TDC to obtain proper combustion. The proper way would be to open up the combustion chamber or dish the pistons. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Yeah like the ones I have <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
<img src="http://james.jaguar.net/kctrading/Pics-of-truck-3-2-02/383-Shortblock/closeup-srp-pistons.jpg" alt=" - " />
31cc dish forged SRP's I run mod vortec steel heads right now that have been milled (57cc chambers) with .008 engine deck height and a felpro .039 gasket to get 9 to 1 comp but I'm running 10psi of intercooled boost on a 383 engine <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
Ken
03-25-2003, 12:42 AM
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Re: Cometic head gasket lowers compression? ..these heads are new, and stock LS6 valves are installed...
I'll be installing them with the motor in the car so...I don't want to install new pistons and do not want to fly-cut them in the car either....
...can't I use a .090 thickness head gasket and install a high-lift cam? ...this is a street car...
I'll be installing them with the motor in the car so...I don't want to install new pistons and do not want to fly-cut them in the car either....
...can't I use a .090 thickness head gasket and install a high-lift cam? ...this is a street car...
03-25-2003, 06:57 AM
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Re: Cometic head gasket lowers compression? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by robertbartsch:
<strong>...can't I use a .090 thickness head gasket and install a high-lift cam? ...this is a street car... </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Sure. Do whatever you want. We're just giving you the right way to do it, but you wouldn't be the first guy to go another route.
Let us know how it turns out with .090 gaskets...
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<strong>...can't I use a .090 thickness head gasket and install a high-lift cam? ...this is a street car... </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Sure. Do whatever you want. We're just giving you the right way to do it, but you wouldn't be the first guy to go another route.
Let us know how it turns out with .090 gaskets...
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03-25-2003, 05:36 PM
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Re: Cometic head gasket lowers compression? ..OK so my other option is to flycut the pistons with an Isky valve relief cutter...apparently, this can be done with the block in the vehicle....
...Has anyone had experience with this technical marvel...????
...Has anyone had experience with this technical marvel...????
03-26-2003, 06:21 AM
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Re: Cometic head gasket lowers compression? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by robertbartsch:
<strong> ..OK so my other option is to flycut the pistons with an Isky valve relief cutter...apparently, this can be done with the block in the vehicle....
...Has anyone had experience with this technical marvel...???? </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Yup. Just bring the piston to TDC and smear grease on the gap between the piston and the bore and cut away. The only danger in doing this is that some aluminum can get caught under a ring land, that's why the grease is necessary. Oh, and the other danger is that you cut too deep into the piston, but you're not looking to cut out very much material. Just don't fall asleep with the cutter running. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />
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<strong> ..OK so my other option is to flycut the pistons with an Isky valve relief cutter...apparently, this can be done with the block in the vehicle....
...Has anyone had experience with this technical marvel...???? </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Yup. Just bring the piston to TDC and smear grease on the gap between the piston and the bore and cut away. The only danger in doing this is that some aluminum can get caught under a ring land, that's why the grease is necessary. Oh, and the other danger is that you cut too deep into the piston, but you're not looking to cut out very much material. Just don't fall asleep with the cutter running. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />
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03-26-2003, 06:23 AM
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Re: Cometic head gasket lowers compression? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by TchargedLS1TA:
<strong> If you want to be cheap about it, get some playdoh and stick about a fist size amount in your C.C. and torque your heads down (with the old head gasket of course).. Crank the engine over BY HAND, make sure your ignition and fuel are disconnected... This will show you your P-T-V clearance.. You can then cut playdoh in half and measure the clearance and use it to position or reference how much you want to cut out of your pistons.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Wish I'd have said that. <img border="0" title="" alt="[Roll Eyes]" src="images/icons/rolleyes.gif" />
SC-
<strong> If you want to be cheap about it, get some playdoh and stick about a fist size amount in your C.C. and torque your heads down (with the old head gasket of course).. Crank the engine over BY HAND, make sure your ignition and fuel are disconnected... This will show you your P-T-V clearance.. You can then cut playdoh in half and measure the clearance and use it to position or reference how much you want to cut out of your pistons.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Wish I'd have said that. <img border="0" title="" alt="[Roll Eyes]" src="images/icons/rolleyes.gif" />
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