is there any sort of relationship between compression and vacuum at idle? would it be correct to assume that a car with low compression, should have low vacuum at idle? say for example... an engine with a compression of 55-60psi (low compression), how much vacuum would i expect to see at idle... or would compression that low even allow the car to start...?

 

Good question, but I don't know the full answer. What I do know is, yes, compression has a relationship to vacuum, but so does air flow. High flow exhaust and intakes can cause lower compression by virtue of less restrictions.
Here's something to keep in mind about low compression rotary engines; normally only one seal causes it, and two rotor faces feel it. So, if you had low compression you would most likely see a fairly noticeable fluctuation in vacuum as the higher rotor face passes. Sorry I could not help.

 

i thought an engine with good compression would see higher vacuum?

 

That is correct. I think Goodfella had a poll going somewhere, where people posted their vacuum readings that they were seeing on their PFC.

 

here it is https://www.rx7club.com/forum/showth...acuum+readings