64-66 273 what pistons do I have ?

[rustytoolss]

Got the heads off my early 273. Never had a 273 apart before. At some point in it's life someone installed open chamber 675 heads and hydraulic parts.
Back to the pistons. They are flat top , with 4 valve reliefs. Look to be .050 in the hole. The pistons are stamped .030.
I'm guess that I've got the 8.8/1 pistons ?
Also how far can I safely mill THESE 675 heads to up compression ? was also thinking of using MR Gasket .028 thin head gaskets. This is just a driver. Would still prefer to use 87-89 octane. Any input

 

[cudavert]

Flat-tops = low comp. With the 4 valve reliefs, open chamber heads and .050 in the hole, I'd bet they're 8.8 at best. Maybe even in the 7's with fat head gaskets.

 

[toolmanmike]

Got the heads off my early 273. Never had a 273 apart before. At some point in it's life someone installed open chamber 675 heads and hydraulic parts.
Back to the pistons. They are flat top , with 4 valve reliefs. Look to be .050 in the hole. The pistons are stamped .030.
I'm guess that I've got the 8.8/1 pistons ?
Also how far can I safely mill THESE 675 heads to up compression ? was also thinking of using MR Gasket .028 thin head gaskets. This is just a driver. Would still prefer to use 87-89 octane. Any input

Mill the heads and don't forget the intake or it won't fit. You need to seriously think about the combination of parts you have. A low compression 273 needs the closed chamber heads and will benefit with a step up in compression. You have neither. With the pistons you have so far down the bores you could mill .100 off the heads before it would do much good. If you want to go completely through the engine put Egge domed pistons or custom flat tops at zero deck. The closed chamber heads and a thin gasket would net the best results. tmm

 

[66fs]

I'd measure how far down those pistons are for sure while you have it open. I put open chambered 675 heads on my brothers 273 and Fel-Pro gaskets to be able to run 87 octane gas. I also mill the heads .020 and the intake side of the heads .019 when I put a street engine together. 1wild&crazyguy measured stock chambers about 68 cc so that puts the chambers about 64 cc. The 920 heads with Fel-Pro gaskets needed premium gas to stop detonation. I am not sure about where the pistons are in the hole on that 273.

 

[toolmanmike]

It must be the polished chambers on my heads that make the difference. I milled the heads .030, used the thin head gasket and have the Egge domed pistons. My timing is 12 initial, all in by 2000 and total at 35° I use Shell premium with no ping problems and have tried regular gas a couple times with no ping. It sounds like Rusty needs a .030 mill and a thin head gasket and it will run all day on cheap gas without pinging problems. tmm

 

[66fs]

It must be the polished chambers on my heads that make the difference. I milled the heads .030, used the thin head gasket and have the Egge domed pistons. My timing is 12 initial, all in by 2000 and total at 35° I use Shell premium with no ping problems and have tried regular gas a couple times with no ping. It sounds like Rusty needs a .030 mill and a thin head gasket and it will run all day on cheap gas without pinging problems. tmm

Maybe I'll try and tune my 66 a little closer if you can run on pump premium. My heads are at 57.4 cc, milled .040 and .038 on the intake. TRW forged 10.5 pistons. I'll need that 10.95 clutch for sure then.