question about thickness of cometic headgaskets

[4-71/Z-28]

heres the scenario: i blew a cometic gasket on my gn ( the ones that were on there wer triple thick i believe .040 thickness), i ordered another gasket and they sent me a .060 cich is 5 layers, can i just take 2 layers out?

 

[turbofabricator]

heres the scenario: i blew a cometic gasket on my gn ( the ones that were on there wer triple thick i believe .040 thickness), i ordered another gasket and they sent me a .060 cich is 5 layers, can i just take 2 layers out?

Maybe you need to use the .060" gasket to prevent it from blowing again? Thicker means less compression which means less detonation. WHY did it blow? That is the FIRST question needing an answer. BUt to answer your question, yes, you should be able to remove a layer or two. Just make sure you use onae thick layer and one thin payer on each side. Copy the removed gasket.

 

[4-71/Z-28]

i lifted a head, so it wasnt really detonation rather than probably the head studs needing retorqueing

 

[DailyDrifter]

I asked this same question about a month ago. Pacecarta said it can be done. I have a .060 gasket and im going to take one of the shims out to make it a .040.

 

[bison]

Thicker means less compression which means less detonation.

Wrong. Ive run .040 gaskets in a 9.3:1 engine and dont ever have detonation. Detonation is from not enough octane or poor tune. If i was at the threshold for detonation with the 9.3:1 engine then i could say lowering compression would eliminate it. I doubt more than a handful of guys in here even came close to the detonation threshold for boost+compression+timing. I know i havent and ive run over 30psi on that combo. Usually the problem is someone didnt use enough octane and got greedy.

 

[Pablo]

Wrong. Ive run .040 gaskets in a 9.3:1 engine and dont ever have detonation. Detonation is from not enough octane or poor tune. If i was at the threshold for detonation with the 9.3:1 engine then i could say lowering compression would eliminate it. I doubt more than a handful of guys in here even came close to the detonation threshold for boost+compression+timing. I know i havent and ive run over 30psi on that combo. Usually the problem is someone didnt use enough octane and got greedy.

9.3:1 and 30 psi on pump gas?

Lower compression gives you a lot more room to work with to compensate for the myriad of factors that can contribute to detonation. Assuming there is any one compression ratio that is ok for hundreds of variables is just plain ignorant. Are you aware of what fuel he is limited to, what kind of inlet temps he sees, what kind of temp rise over the course of a run, camshaft, etc etc? Increased static compression lowers your detonation threshold while dynamic compression can change that threshold regardless (though not necessarily mutually exclusive) of what your static compression ratio is.

You can certainly run 9:1 cr on just about any turbo buick depending on how much boost you run for your given combo and conditions. Everyone wants more performance though and depending on some combinations it would certainly be advisable to run less or more CR depending on the desired effect. The increase in chamber pressure and temperature due to increased static compression is much less desirable than an increase in boost resulting in the same power increase. More static cr = greater deviation from the mean cylinder pressure (at the high end) and you cant intercool the resultant heat from doing so like you can with an intercooled turbocharger setup

 

[4-71/Z-28]

I asked this same question about a month ago. Pacecarta said it can be done.

good enough for me, pacecarta helped put this engine together, he definatly knows his stuff

 

[bison]

9.3:1 and 30 psi on pump gas?

Lower compression gives you a lot more room to work with to compensate for the myriad of factors that can contribute to detonation. Assuming there is any one compression ratio that is ok for hundreds of variables is just plain ignorant. Are you aware of what fuel he is limited to, what kind of inlet temps he sees, what kind of temp rise over the course of a run, camshaft, etc etc? Increased static compression lowers your detonation threshold while dynamic compression can change that threshold regardless (though not necessarily mutually exclusive) of what your static compression ratio is.

You can certainly run 9:1 cr on just about any turbo buick depending on how much boost you run for your given combo and conditions. Everyone wants more performance though and depending on some combinations it would certainly be advisable to run less or more CR depending on the desired effect. The increase in chamber pressure and temperature due to increased static compression is much less desirable than an increase in boost resulting in the same power increase. More static cr = greater deviation from the mean cylinder pressure (at the high end) and you cant intercool the resultant heat from doing so like you can with an intercooled turbocharger setup

110+ octane and alky. More compression will mean more power everywhere in the curve. If you want to use pump gas then you better not go over 24-25psi unless you are spraying a lot of alky in there. Even with that you are still at greater risk for detonation than the high octane gas. By reading his sig with a 70GTQ and a small hydraulic cam i assume he will be running high boost to get the number since he is rpm limited by the valvetrain. If you are octane limited you are much better off with a solid cammed engine that will rev higher and run less boost if you want to come close to maximizing the compressor. The 2 ways i know of to get more mass flow into the engine are to turn up the boost and or rev the engine more.

 

[Pablo]

110+ octane and alky. More compression will mean more power everywhere in the curve. If you want to use pump gas then you better not go over 24-25psi unless you are spraying a lot of alky in there. Even with that you are still at greater risk for detonation than the high octane gas. By reading his sig with a 70GTQ and a small hydraulic cam i assume he will be running high boost to get the number since he is rpm limited by the valvetrain. If you are octane limited you are much better off with a solid cammed engine that will rev higher and run less boost if you want to come close to maximizing the compressor. The 2 ways i know of to get more mass flow into the engine are to turn up the boost and or rev the engine more.

More compression will mean more power assuming detonation doesn't occur. It is an unfortunate fact of life that it indeed can occur. If we are to take your point to its logical end, then where is the limit on CR and why dont we all run 11:1 in our buicks?
The fact of the matter is that while compression can increase power, so can increasing boost. Fortunately, boost can be intercooled, it also has the effect of increasing average cylinder pressure more evenly throughout the stroke. Increased static compression vs boost has the effect of a rapid rise in chamber pressure and temperature as the piston approaches TDC. This makes the fuel in the chamber much more volatile and thus more prone to detonation.
The downside to reduced compression is less power off boost and slower spool. There is clearly going to be a lower limit depending on your needs.
This concept of arbitrarily assigning boost pressures that are safe or not is also oversimplifying what goes on in an engine. Boost is not a measure of chamber pressure. What boost level may be fine on one combo due to restrictive heads and cam may blow out the head gaskets on a more efficient setup. FYI on my stock longblock I ran over 25 psi and generally 28 on a single methanol nozzle ( and 91 octane) for 4 years without trouble. It took a 95 degree day at the track to finally pop an HG.

 

[bison]

More compression will mean more power assuming detonation doesn't occur. It is an unfortunate fact of life that it indeed can occur. If we are to take your point to its logical end, then where is the limit on CR and why dont we all run 11:1 in our buicks?
The fact of the matter is that while compression can increase power, so can increasing boost. Fortunately, boost can be intercooled, it also has the effect of increasing average cylinder pressure more evenly throughout the stroke. Increased static compression vs boost has the effect of a rapid rise in chamber pressure and temperature as the piston approaches TDC. This makes the fuel in the chamber much more volatile and thus more prone to detonation.
The downside to reduced compression is less power off boost and slower spool. There is clearly going to be a lower limit depending on your needs.
This concept of arbitrarily assigning boost pressures that are safe or not is also oversimplifying what goes on in an engine. Boost is not a measure of chamber pressure. What boost level may be fine on one combo due to restrictive heads and cam may blow out the head gaskets on a more efficient setup. FYI on my stock longblock I ran over 25 psi and generally 28 on a single methanol nozzle ( and 91 octane) for 4 years without trouble. It took a 95 degree day at the track to finally pop an HG.

Even at 30 psi the engine wasnt close to detonation. It would take around 40 psi on that combo to even come close to the detonation threshold. Anyone who wants to make the power while trying to skimp on octane will be in for very frequent expensive lessons. My stage 2 is almost 10.0:1