Head Gasket Bore Size?
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Staging Lane
Joined: May 2009
Posts: 96
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Head Gasket Bore Size? How do you know how much bigger a head gasket bore size you should go? I see the Cometic stuff available in just about any bore and thickness you want. I've also seen some head manufacturers recommend a certain size bore, but not all manufacturers do this.
I wanted to decrease the compression on my engine and go to a thicker .06 or .07 thickness (along with adding a 72cc head) for adding a supercharger, but does the overbore of the headgasket really matter. It seems if you go to big, you only create a dead spot in the cylinder head with no swirl, but it is such a small volume.
BTW, this is for a 402 with a 4.01 bore.
I wanted to decrease the compression on my engine and go to a thicker .06 or .07 thickness (along with adding a 72cc head) for adding a supercharger, but does the overbore of the headgasket really matter. It seems if you go to big, you only create a dead spot in the cylinder head with no swirl, but it is such a small volume.
BTW, this is for a 402 with a 4.01 bore.
It all depends on the heads you choose. Some heads require a 4.130 gasket because that is how much the chamber is opened up too. If you put a 4.06 gasket on, it might burn some gasket.
On adding a thicker gasket, how much are your pistons out of the hole, or in it? If you are just say 0 deck and add a .06 gasket you might run into detonation problems.
On adding a thicker gasket, how much are your pistons out of the hole, or in it? If you are just say 0 deck and add a .06 gasket you might run into detonation problems.
The pistons might be rated at 0 deck but that is not where they are at. The ls2 block is rated at 9.240 deck height, but it almost never is that. You could have one side at 9.238 and the other side be 9.234. If whoever build your engine decked them both at 9.234 then you just became .006 out of the hole.
What kind of head is on the motor? Bore for the heads and motor is needed in order to make sure the gasket is correct. I will go ahead and say we don't really like to run a gasket thicker than .060".
Thread Starter
Staging Lane
Joined: May 2009
Posts: 96
Likes: 1
My short block is a TSP 402 with Wiseco -10cc pistons. The spec sheet says 4.0 inch stroke and 4.01 inch bore. It slipped my mind to actualy measure the deck clearance when I had the heads off so I called TSP and asked what the pistons were spec'ed to and the guy said zero deck clearance, so I assumed that was good enough.
Currently it has a set of PRC 5.3 heads on there, but this has a bit more compression than I would like for a supercharged engine. So it will probably get a set of PRC LQ9 heads.
If it really turns out to be that big a deal, I can pull the heads off and take an actual measurement.
Thanks for the tip on running the .06 thickness gasket. I was thinking .07, but the .06 still puts me under 10 for compression. I think it was like 9.7.
Currently it has a set of PRC 5.3 heads on there, but this has a bit more compression than I would like for a supercharged engine. So it will probably get a set of PRC LQ9 heads.
If it really turns out to be that big a deal, I can pull the heads off and take an actual measurement.
Thanks for the tip on running the .06 thickness gasket. I was thinking .07, but the .06 still puts me under 10 for compression. I think it was like 9.7.
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For that motor and head selections you are talking about a GM LS9 gasket would work, or if you want aftermarket cometic has the 4.035" bore available that would fit. Keep in mind if you go with the thicker gasket most of the time it takes a couple weeks to get because we don't keep them in stock that thick.
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Staging Lane
Joined: May 2009
Posts: 96
Likes: 1
For that motor and head selections you are talking about a GM LS9 gasket would work, or if you want aftermarket cometic has the 4.035" bore available that would fit. Keep in mind if you go with the thicker gasket most of the time it takes a couple weeks to get because we don't keep them in stock that thick.
BTW, the 402 purrs nicely with the PRC 5.3 heads. The throttle response is sweet!
