NA vacuum pressure, Quick Question Options

[Bigmeanbulldog55]

I've happend apon a cheap boost gauge that messures up to 30+ & -. I'm wonding if this is enough to messure the vacuum pressure. I'm worried that it won't. I just want to know the deference in pressure as the rpms go up or down.

[Jaws4God]

well i got them installed today.. but little confused.. looks like the vacuum will read about 22 when idling.. and when i gas it it jumps down closer to 10 or 5.. but I thought if I left the gas there then the vacuum will stay there.. IE, the more gas the less vacuum...but if i give it steady gas it seems to jump down to 10 ish then go back up to 20.. is that normal?

i'll drive it tomorrow to see how it does..

[Yellow94GT]

well i got them installed today.. but little confused.. looks like the vacuum will read about 22 when idling.. and when i gas it it jumps down closer to 10 or 5.. but I thought if I left the gas there then the vacuum will stay there.. IE, the more gas the less vacuum...but if i give it steady gas it seems to jump down to 10 ish then go back up to 20.. is that normal?

i'll drive it tomorrow to see how it does..

22 inches at idle is good. When reving a parked engine a rapid return to high intake manifold vacuum (above readings at idle) is normal.

On the road the engine will give the readings you may anticipate due to engine load and vacuum characteristics. As you drive with Wide Open Throttle (Accelerator fully depressed) there will be virtually no engine vacuum. Zero inches indicates that there no difference between the normal atmospheric (outside the engine) pressure and the pressure (within the engine) at ported intake manifold source.

However as rpm increases at part throttle vacuum #'s will rise (unless the engine is at W.O.T.)
The extreme case is when you downshift and let off the throttle the readings will read somewhere around 30 inches until engine rpm decreases and/or the throttle is opened.

You'll soon see this as you drive and watch the readings when you drive.

The vacuum gauge is a good diagnostic tool. It can indicate if an engine is running properly. Many common engine problems can be discovered/ noticed and then diagnosed with the aid of a vacuum gauge.

Yellow94GT

This post has been edited by Yellow94GT: Oct 24, 2006 - 2:09 AM