Customer head gasket.

[Steve.k]

On custom head gaskets do you have a rule of thumb over bore size? Eg most 4” bore are 4.1. Do you stick with .100 or tighten as close to bore as possible. So on 4.155 go 4.2? Thoughts please.

[ProPower engines]

It depends on the use. If you are doing a spec deal when comp. is limited then keep it as tight as possible.
If its not and you can get away with a shelf type gasket then use them.
If you are talking about MLS gaskets there are some with a bore relief and other not.

I don't go more then .010 larger then the bore unless I have to a shelf gasket that has a much larger gasket bore size.

[Steve.k]

Thank you. No spec as much squeeze as we can safely get.

[BillK]

Also depends on how much chamfer on the top of the bores. A lot of stock blocks have gigantic chamfers. A .030 chamfer adds .060 to the diameter.

[englertracing]

Ive been told to stay 0.010" over if the piston is anywhere near the deck

[Schurkey]

If the block has had the cylinders moved around to maximize wall thickness, I'd expect to need a larger-bore gasket, since the bores in the gasket aren't going to be shuffled to match the cylinders.

There are offset dowel pins, but I've never used them.

[CGT]

Also depends on how much chamfer on the top of the bores. A lot of stock blocks have gigantic chamfers. A .030 chamfer adds .060 to the diameter.

Yes and some machine shops get WAY carried away with that.

If the block has had the cylinders moved around to maximize wall thickness, I'd expect to need a larger-bore gasket, since the bores in the gasket aren't going to be shuffled to match the cylinders.

There are offset dowel pins, but I've never used them.

I just recently had to use a head gasket with a larger bore than what would normally be necessary due to using offset dowel pins. I may try fitting a smaller bore gasket next time around or talk to cometic about possibly making one.

[zums]

You should request the shop leave the bores un chamfered and hand chamfered it yourself, I've been doing it that way for years, run the gasket to the bore edge ,as CGT pointed out , sometimes you are forced to run oversized because of offset dowels or in. bore notching

Tom

[CGT]

You should request the shop leave the bores un chamfered and hand chamfered it yourself

Exactly. I also only use bore specific tapered ring compressors anymore...don't really need much if any chamfer with those. Back in the day, I had the local machine shop "fix me up" with a huge chamfer on a GM 400 block that I had some decent money invested in with billet caps etc... NOT a good application to have big chamfers on . I thought I was gonna kill him

[Steve.k]

Thanks everyone. Talked to mfg and we went with 4.180 for the 4.155 bore. We sitting about .006 above deck.