I found a really good deal on a tial bov and I wanna buy it as soon as I can, but I wanna make sure that the spring in it would be okay for my application. I know that choosing the spring is based on idle vacuum, but I cannot run my car at this moment to check if the idle vacuum is on the higher end or the lower end.

My question is this how does compression ratio affect idle vacuum? Just in my mind I would think that the lower the cr the higher the idle vacuum (in absolute terms). If I am right then my cr which is ~9.5:1 would need one of the lower/middle spring rates (7 or 9psi) on the tial bov and hopefully the 7psi spring would work for me (because that is the spring that it has in it).

I will be running 15-16psi boost maximum and at this boost the turbo will be flowing ~42-43 lb/min. Thanks for any help.

Oh, and btw, I searched for sometime but found nothing.

 

No input on how compression ratio affects idle vacuum?