Custom headgaskets for custom bore size

Do I have to get custom headgaskets made for an engine if I have it bored out? Are there any alternatives like say modifying an existing headgasket to match bore size? Mazda 1.8 bp-z3 engine.

I will give a general answer because you told us nothing about the type of engine.

Head gaskets will generally be larger than the standard bore. Overbores will usually fit and seal properly. Sometimes aftermarket head gaskets will specify they are for an overbore.

If this is an older Chevy or Ford V8, you can buy dozens of gaskets for different bores, head materials and more.

Sorry I was kind of just asking in a general sense but if it helps more im the motor would be a mazda bp-z3 engine.

I think the shop that does the work might have a real answer about the gasket . Also you could just keep the old gasket and see how it fits after the rebore .

True but im probably gonna go a little bit further past the max overbore because I was told you could if you installed wet sleeves to your cylinders but im not completely sure if thats true or not. So at that point im pretty sure the stock gasket won’t fit anymore.

Use the internet to see if you can find performance gaskets. If its a popular engine to modify, someone may make gaskets for the mods you plan. You may be able to get a custom copper head gasket cut on a water-jet cutting machine for the engine.

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Just some food for thought but maybe it should not be bored too much. Boring the cylinders out does not really add that much to the horsepower equation. I’ve heard a few people over the years claim that horsepower increased quite a bit just from boring .020, .030 over, etc. Not really.

Porting the heads, larger valves, intake/exhaust mods, camshaft profile change, and so on is where the major changes come into play.

I’ve modded a Cadillac 500 engine by adding 425 cylinder heads to it. That raises the compression ratio by 2 points and the stock 500 head gaskets are used. The only mod there is to drill a couple of extra coolant holes in each head gasket but the stock head gaskets work just fine.


Thank you for the advice I will keep it in mind.