normal cyl compression

[BUCKWHEAT]

what PSI should we expect on a healthy MM engine? 180? 160? 140? What PSI average have you seen in the real world? Thanks.

[crouse]

When I did mine, I was in the 180-200 range.

[fastblackmerc]

What's more important is the variation between the lowest and highest cylinders. Shouldn't vary more than 10%.

[crownvic97]

The numbers themselves don’t matter much, different gauges tend to read differently. It’s variation between cylinders you are checking.

I had 200 in 1-6, 170 in 7, and 90 in 8. That was a problem!

[fastblackmerc]

The numbers themselves don’t matter much, different gauges tend to read differently. It’s variation between cylinders you are checking.

I had 200 in 1-6, 170 in 7, and 90 in 8. That was a problem!

#8 is always a problem unless you've installed a rear cooling mod.

[crownvic97]

#8 is always a problem unless you've installed a rear cooling mod.

Indeed, I have rear cooling mods on the back of both heads now...after getting new heads.

[BUCKWHEAT]

Thanks for the comments. My range was tight, 136 average, with 142 high and 132 low. My gauge is a Harbor Freight special....

Did a leak-down today. Three at 20%, balance under 10%. Smoke test suggests the leakers are exhaust valves. Not critical.