The Mighty 258 > The Engine

cylinder compression?

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mihunter:
does anyone know what the cylinder compression should be on the 258? thanks

mudkicker715:
Assuming stock 160 to165 psi.

ammachine390:
For an 81 258, the compression should 120-150 psi with 30 psi max variation between cylinders.

BenM:
The earlier engines will be less, they went to higher compression heads it 82. Very early AMC engines were about 8.0:1, by the early Eagles it was 8.2:1, and the post-81 Eagles were 8.6:1.

Jurjen:
So considering that both inlet and exhaust valves are already closed in BDC, you can multiply the ratio by the ambient air pressure: 15psi.
Ratio 1:8 should give you 120psi.
Note that ambient is much lower when your living in the hills.

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