Slant six compression

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Slantsix64

Slantsix64

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hey there guys was going to pick up a six motor checked it out runs good did a compression test 140 psi average on the cylinders. my question is if the motor has 140 psi what the compression ratio on the slant would this indicate that the head has had some milling done to it or is that just stock psi on a regular rebuild on a 1971 slant six 225. i am asking this cause the owner only know the person he got it from did a rebuild prior. any advice is welcome thank you!
 
There really isn't a direct correlation to compression ratio and cylinder pressure. Too many variables. Most slants had an advertised ratio of 8.4:1.
 
You might get an approximation of the total cylinder volume if you knew exactly when the intake valve closes. Then you could work the Dcr formula backwards. But it would be a lil complicated and a long-shot for sure.
140 is a pretty good number, for slanty.If she's got oil pressure, she'd be worth driving, for sure.
 
The advertised CR may be 8.4:1 but not for real.

We milled our /6 head .050" at last January's rebuild, and with stock .040" over pistons, we got 130 psi across all cylinders, and that is at or slightly above FSM numbers. (I did forget to prop the carburator open so it could be a bit higher.) So if you got 140 psi then that is good; it could have had the head shaved. Or, the compression gauge may not be totally accurate, or they did not run the compression test 'dry' and put oil in the cylinders to make the rings seal better! Either way, it sounds like it has decent cylinder sealing; if you have doubts, ask for a cylinder leakdown test.
 
How can you get an earlier closing than a stock /6 cam? LOL

Actually the 60's /6 cams were milder (less lift, can't recall the duration).
 
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