I have a sleeved 388ci LSA with a 4.125 bore using an F1X. What is the best head gasket for 4.125 bore? I pretty much see stock or Cometic. I really wish I would have stuck with the stock bore so I could have used the LS9 head gasket because it has more layers. I've heard some people get away with using the LS9 head gasket on a 4.125 bore but not sure if I want to attempt it even though it would be nice if it did work.

 

I would get Cometic they are so good I reuse them.

If they don't have the bore size you call them and they make any bore size you want and you have them in a week they also have several compressed thickness to choose from.

They made two sets for me so far last one was 0.045 compressed, already reuse one of them no problem.

 

LS9 Gasket has a 4.100" bore, I would not recommend using that on a engine with a 4.125" bore. Even if the parts stack zero's with the deck height (which 99% of the time does not happen for multiple reasons) it would not be a good idea.


I would personally just use a stock LS7 gasket with head studs, ive never had good luck with cometic gaskets.

 

Is it a six bolt block. You can use the GM LSX gaskets

 

4 bolt block. Lsa block sleeved to 4.125

 

LS7 it is then

 

I would use the OEM LS7 head gaskets, blew some cometics last summer and still can't seem to find what caused it. I have head studs also.

 

Or just use the LSX gaskets and have the extra bolt parts just sticking out. It won't hurt anything.

 

How many layers does that gasket have? Found the part number but it just says multi layer.

 

Never counted, but plenty of people making 1500+rwhp on them without issue.

 

I use OEM LS7 head gaskets

 

Ha! 4 bolt block blown head gasket? you are lifting up the heads I bet you the leakage is between the studs on the outside of the heads.

The very reason there is 6 bolts heads and no you are nut stretching the studs there's never leaks around the stud area but between rite about in the middle happened to me many times even with O rings on the heads and the block and copper head gaskets I have lifted the 4 bolt heads enough to leak past the O ring what's worth is ones the head lifts will continue to lift.

Here's a tip you may or not believe this but the head can lift and the block can stretch and to know who is doing what you observe the head gasket and see which side is leaking, IF the black smoke trail is on the top part of the gasket the head is lifting, IF the smoke trail is on the under side the block is stretching.

I'm sorry to be the one but I done it all and all that could happen have happened to me did not learn this in school but building and racing engines, before there was 6 bolts heads I made the heads into 6 bolts and so did the block.

Today 6 bolt heads and block is my choice unless is a heads and cam on a stock block and still if I buy heads will only get 6 bolts juuuust in case later I decide to amplify power.