whats a good vacuum reading /oil pressure ?

[sports-imports]

My car is now fully registered and road legal , so im able to pay more attention to driving the thing rather than having it sat in my garage.

So whats a good vacuum reading for these engines ? Mine only makes 300mmHg at idle which i think is a little low, and 500mmHg under decel. Ive got nothing to compare it to exepct my RX7 which is just plain weird anyway.

Oil pressure just over 2 bar when warm at idle and 4bar at 3100rpm. Normal?

Ive got an HKS VPC too , so any air leaks arent immediately apparent. Havent tried it on boost yet - need to get it set up for UK fuel. Cant wait though

Chris

[jrpidgeon]

Vacuum is a little low, as an example my car makes just over 500mmHg at idle.

Oil pressure is fine, if your talking about warm pressures?. If cold that is maybe a little low aswell.

The VPC works with a pressure transducer tapped into the plenum so any air leaks are going to effect the fuel Map, accross the whole rev range.

[sports-imports]

Ah ! I thought that was a temperature probe for the VPC. I was assuming it was using a seperate map sensor somewhere.... i understand now !

Ive got HKS cams and variable cam gear - im thinking this could make the vacuum lower ? Or am i barking up the wrong tree again ? The car idles fine and drives fine, and it IS a very old Greddy gauge (ive no stock boost gauge).

I'll get under the bonnet at the weekend


Chris

[SkylineUSA]

Which cams do you have? Do know where your LSA is at? Yes, duration, lift and timing events will play with your idle vacuum.

My oil gauge will read 1 at idle sometimes. I would not worry about where yours is at. Its a well know fact that the factory gauge is not that accurate. As long as you don't hear guys trying to hammer there way out of your engine you should be fine with your oil pressure

[gary]

ah another vpc user,
the probe in the manifold is for air temp and it does have a seperate map sensor from the manifold,the low reading you have is due to your wild cams and timing,sounds like another monster
Gary

[Peter]

Mine makes 300mmHg on idle too.... Forgot to check it on run down though.

[gary]

Youre just trying to squeeze too much out of your cams

[Peter]

Haven't touched them myself Gary. How does the cam timing affect the vacuum, is it the overlap?

Peter.

[gary]

The cam timing effects a whole lot of parameters overlap and vacuum are related but thats just the tip of the iceburg
Gary

[Peter]

Thanks Gary.

What are the disadvantages of having a low vacuum?

[gary]

heavy fuel consumption and response and incomplete combustion,
also could be bore wear etc
Gary

[Peter]

Originally posted by gary
heavy fuel consumption and response and incomplete combustion,
also could be bore wear etc
Gary

Oh, not much then.... Guess I must just be plain lucky she keeps going strong and doesn't blow up like so many, with good response, fuel consumption and a clean backside..

I'd be interested to learn what vacuum everybody else is getting at idle....

[SkylineUSA]

Too low of vacuum, no brakes. Well at least the car I am used to working on, i would think the same for Skylines.

Your LSA and duration plays a biggest part than anything else in low vacuum.

[sports-imports]

I thought my cams might have something to do with it. Ive since found that the more the overlap, the lower the manifold vacuum. Im learning quickly !

I dont know if HKS specify the LSAs on their cams, usually just the duration - 240, 260 or 272 deg from memory. Mine allegedly has 240deg cams, but the idle is quite rough, so maybe 260s ?

High fuel consumption is right - no figures but 6% CO at idle and not many miles per gallon

Chris

[jrpidgeon]

Looking at the turbo's I'd say more like Step 2 272 maybe 280 espically if its got a burbley idle, nice