compression ratio

[erictheetype]

chassis no 1e51060 engine no 7e53798-9 should the compression ratio be 8:1 or 9:1

[PoB]

If the last digit is 9 then 9:1 CR

[TonyB]

The actual compression ratio depends on the pistons fitted but also whether the head or block faces have been refaced. Most of the heads will have been machined by now. The compression ratio that is best for your engine depends on what fuel you intend to use, the ignition advance you use and the type of cams you have. In my experience, with standard cams 8.5:1 is enough for standard fuel unless you pull the ignition back.

[SJHill99]

Most books I've read list 9:1 compression ratio as standard for Series 1 4.2L, with 8:1 available as an option. Does anyone have any idea as to how many Series 1 4.2 RHD cars were supplied with 8:1 compression ratio heads. Is it listed anywhere? Why would you specifically opt for an 8:1?

[piman]

Hello SJHill,

it's not the heads but the pistons that determine the compression ratio. I suppose someone abroad who has only lower octane fuel could be one reason?

Alec