anyone with high compression seen a variation in vacuum pressure at idle? I am running a 12.4:1 cr. I can't find any vacuum leaks yet my gauge says 15inHg at 750rpm idle. this is a bit different from what my engine use to run (22inHg) with the 9.5:1 cr.

thanks for any input

 

Did you change camshafts along with the compression upgrade?

 

no, stock cams......any idea?

 

bump

 

it dose sound like a cam isue. so your cam timing line up right. maby a cam gear slipped.

 

really, cams can cause this problem. anyone else heard of this?

 

would like to know more about this too, after installing an ITB setup vacuum changed from 15psi at idle to 8psi... what to do/how to compensate a/f readings with lower vacuum pressure?

 

bump, any ideas?

 

bump for good question

 

did u have any head work done? particularly a valve job?

 

Big cams will deffinitely lower your vacum pressure, messed up timing will too. Losing vacum pressure cuz of cams is mostly a problem for the V8's since none of them have v-tec, one cam lobe for every rpm makes for alot of lift and overlap at idle and the motor can't make vacum. I think u have a problem, like a leak or bad timing, your idle speed should also be wierd too.

 

Does higher compression increase reversion back into the intake? If it does, perhaps that is what is causing it.

Verified cam/crank timing?