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]

I'm not sure if its the same for all cars, but my friends GTI has stock turbo and he installed a boost gauge on his. He said its suppose to read -20 when idling and yes it goes to 0 when he is accelerating and depends on how much gas he gives it.

(but his goes to 10psi cuz its boosted) but I believe he did install it on his stock Mazda which wasn't turboed yet and it would go to about 0 when accelerating..

I have a Vacuum gauge coming and if I can get it installed easily, i'll let you know what I find out

Thanks!

[Bigmeanbulldog55]

I had a feeling it was around that. That's what I've seen on my buddies 240. A good bit of negative just at idiol.

[presure2]

at warm idle, a 5sfe should see between -18 - -22 just FYI, bulldog

[Jaws4God]

do you all have a pic of how to run the hose to read the vacuum? i'm not sure how to do that when i get the gauges...

what about the volt?

thanks!

[Bigmeanbulldog55]

at warm idle, a 5sfe should see between -18 - -22 just FYI, bulldog

Do you think I would just snap the gauge if I put it on there like it is? Or would it just max and that be the end of it?

do you all have a pic of how to run the hose to read the vacuum? i'm not sure how to do that when i get the gauges...

what about the volt?

thanks!

I will let you know as soon as I put it on. I might even strap a leaf blower on there to see if I can create positive pressure, just for kicks. I'm also going to test my ram air system, vs just my short ram intake. I hate how those are named the same. I think this gives me the chance to really play with things.

EDIT: Jaws, what do you mean by volt? Do you mean my volt gauge? Because I don't have it on yet either. If you're talking about power to the gauge, I'm just going to tap into the fuse box and use the gauge light fuse.

This post has been edited by Bigmeanbulldog55: Oct 16, 2006 - 7:50 PM

[presure2]

at warm idle, a 5sfe should see between -18 - -22 just FYI, bulldog

Do you think I would just snap the gauge if I put it on there like it is? Or would it just max and that be the end of it?

do you all have a pic of how to run the hose to read the vacuum? i'm not sure how to do that when i get the gauges...

what about the volt?

thanks!

I will let you know as soon as I put it on. I might even strap a leaf blower on there to see if I can create positive pressure, just for kicks. I'm also going to test my ram air system, vs just my short ram intake. I hate how those are named the same. I think this gives me the chance to really play with things.

EDIT: Jaws, what do you mean by volt? Do you mean my volt gauge? Because I don't have it on yet either. If you're talking about power to the gauge, I'm just going to tap into the fuse box and use the gauge light fuse.

everything will be just fine.
you'll never see more than -25 or so.

[n1ckz0r]

bulldog, please post your results when you get them. THats a good idea man.

[CarneDeBlaQ]

I've got a boost/vacuum gauge on my 90 5sfe gt. At idle throttle it reads nearly -30psi. Full throttle is always 0psi. I have a ebay cold air intake sucking air from custom hood scoop. No box, so won't get ram-air, but it is a very short length of pipe and it keeps the intake manifold nice and cool.

[Jaws4God]

I've got a boost/vacuum gauge on my 90 5sfe gt. At idle throttle it reads nearly -30psi. Full throttle is always 0psi. I have a ebay cold air intake sucking air from custom hood scoop. No box, so won't get ram-air, but it is a very short length of pipe and it keeps the intake manifold nice and cool.

Do you have a picture of it installed? i'm still wondering what line to tap into to get the reading..

[hitcachi]

If you need more, let me know.


oh Jaws, and about the volt gauge. You really dont have to make it all that complicated. Just hook it into the same source where you hook the postive wire for the guage backlights. Examples would be, cig lighter, or dimmer switch. As long you make a real good ground, you'll be fine.

[CarneDeBlaQ]

Hitcachi's location is fine, but you can hook it up anywhere off the manifold. I eliminated all emmisions crap so I had some extra places to plug into.

[Jaws4God]

Cool!! thank you hitcachi thats exactly what I was looking for!

So how did you run it throught he firewall? I just thought of that :-P

[hitcachi]

the boot for the steering rack and pinon. Props to Dustin for letting me know on that one a long time ago

[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

[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..

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

YOU DA MAN!!

Drove it to work today, you were right.. it did what I expected... Thanks!!!

[Yellow94GT]

YOU DA MAN!!

Drove it to work today, you were right.. it did what I expected... Thanks!!!

NICE!
Nothing like an invigorating commute to make the day complete.

Yellow94GT

[Jaws4God]

YOU DA MAN!!

Drove it to work today, you were right.. it did what I expected... Thanks!!!

NICE!
Nothing like an invigorating commute to make the day complete.

Yellow94GT

just hope i don't wreck.. its so fun to watch it go from 25 at backpressure to 10 or 5 when I need to gas and go..to 20 when idling...