boost & vac gauge readings

#391 · 03-28-2007, 06:39 PM

I just installed an aftermarket boost/vac gauge.

What should I be seeing on the gauge for:

1. vac at idle
2. max boost

I have Autothority Stage II chips, if it matters. Everything else engine-wise is stock.

Bonus question: I had the turbo rebuilt over the winter, and it hasn't been used yet. What boost level should I keep it under, and for how many miles (to break it in)?

This will be track use only.

soxnail · 03-28-2007, 08:13 PM

Vac = low end 16 inches high end 18 inches. If it is less than 16" you have a leak some where. (this is warmed up car, no a/c or any other load).
Can't answer the boost question, check with the chip supplier.
Never heard of turbo break in, but then it might be my ignorance.
Sox

AaronM · 03-28-2007, 09:53 PM

Sox, I'm usually pulling about 20 inches of vacuum at warm idle. 18 inches of vacuum is for cold idle when the car is just started.

16 inches of idle will let the car run OK, but it'll be a little stumbly. 16 inches of vacuum at warm idle definitely means a leak somewhere. I'd say that less than 18 inches at warm idle means a small leak in one of the little lines.

#391 · 03-29-2007, 03:34 AM

I'm getting about 14 cold, 18 warm for a vac reading at idle. All my lines have been replaced with the Lindsey Racing silicone lines. Should I zip-tie the ends of the vac lines onto the nipples? Does this help? I have seen some people do this.

Another question: Will the vac reading vary depending on where in the vac system the gauge is tapped into? I have removed my heater and AC components, so I hooked the gauge into the "T" connector by the brake booster where the climate control line connected. This way I didn't have to splice into the KLR line like a lot of people do.

soxnail · 03-29-2007, 06:16 AM

AaronM You have a very good system or your gauge is a tad off. Any way I was just giving the minimum for a well secured (leak wise) system.
#39 Your readings are fine, you might have a small leak in the throttle body, tps, idle valve connector(on top) or fuel purge valve. I have used the little spring ties on my small lines see pics.

AaronM · 03-29-2007, 07:26 AM

Quote:

Originally posted by soxnail
AaronM You have a very good system or your gauge is a tad off. Any way I was just giving the minimum for a well secured (leak wise) system.

Sorry if I came off as trying to call you out. I did have the vacuum lines re-done by Gerber last summer so the system is very fresh, which may be what's giving me the stronger numbers.

I'll look into the gauge itself as well. How would I go about calibrating it anyway? It seems basically accurate, sits at "0" with the car off (fully mechanical guage) and Seattle is essentially at sea level.

#391 · 03-29-2007, 07:41 AM

Quote:

Originally posted by soxnail
[B]AaronM
#39 Your readings are fine, you might have a small leak in the throttle body, tps, idle valve connector(on top) or fuel purge valve. I have used the little spring ties on my small lines see pics.

Ah, those spring ties are pretty trick looking. I like the fact that they apply even pressure all the way around...nice. I will look into those, thanks.

Anyone have any idea on my question regarding the break-in procedure for a newly rebuilt turbo? What boost pressure should I keep it under, and for how many miles?

Thanks in advance!

soxnail · 03-29-2007, 10:03 AM

AaronM lol

did not think you were..the gauge will sit at zero because unless you have a "one side sealed" it just reads the vacuum relative to the ambient pressure. The sealed ones require you to set the actual pressure manually at the spot you are. So it reads absolute and that will change with your elevation, the relative gauge will not.
(like setting barometric pressure on a airplane altimeter).
Any way you are probably getting the right numbers as your car is freshly done. If really you want to know there are a couple of things you can do.
1) Take it to calibration lab.
2) take it to the local airport and a shop that fixes instruments and have them check it.
#39 I got mine at a local hardware store..
Sox

ae1969 · 03-29-2007, 11:59 AM

Very cool clips...

I sit at 15mmhg at 3000 feet if it makes any difference?

soxnail · 03-29-2007, 09:30 PM

Ae1996 thats cause the outside pressure is lower so the relative shown on your gauge is also lower. I bet when the car is off it shows 0 and not a vacuum of aprox 3.12 inches (standard lapse rate)
Sox

nize · nize's Garage

an easy way to test boost/vac gauge accuracy is to use a hand pump that also has a gauge, and compare the two readings.