Re: mariner v6 150 compression?
Between 125 and 135, depending on the head gasket thickness. As long as all cyl's are very close to even, less than 10% variation, it should be fine.
Some have the heads milled/planed to raise compression to 145 to gain a bit more performance. Not really recommended for the average boater as fuel quality, ignition timing can become issues.
Generally kept stock as a rock is just fine.
