Low Comp. pistons

[74390]

Is there such a thing as a low Comp. piston for a Amc 390 to make about a 9.3 ratio with 58 c.c. 401 Heads ?

[Big Bad AMX]

I'm not aware of any off-the-shelf. You can have them custom made. If you want to run straight pump gas, it's better to get the compression down with pistons and heads. Thick headgaskets can be trouble. Having said that, the stock 68, 69 pistons are 10.2:1, the '70 had 10.0:1 so you'd be getting a 9.4 with the '70 pistons which is closer to your goal. BUT I think the pin height is different between 68/9 and 70 pistons due to the increased block height on the 70 block so I don't think they'll work for you, someone else should verify that though.


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[jeremy0711]

you didn't mention what engine you are looking for pistons for. if you use the factory 69 and down piston and compression with the 58cc later heads from 71 on up then you are where you want to be at 9.3.

if you use the 70 head 51cc (291c head) then you will acquire what you already have.

if you are using a 71 up based 360-401 engine that is already at low compression then use the 70 head (291c )to get 9.2 compression.

[jeremy0711]

if you are playing with a 70 engine 360 or 390 then you want to use the 58cc head too for the 9.2 compression.