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View Full Version : new boost gauge reading 20 lbs vaccum?


ncrk
02-10-2008, 10:15 PM
ok, i just "installed" an autometer boost gauge, and i drove my car for the first time and it reads between 10 and 20 lbs of vaccum
i doubt my car is pulling 20 pounds
if it helps, my turbo is the t25 that comes stock with the redtop sr20
any help would be cool
thanks

duffman1278
02-10-2008, 10:16 PM
Wrong section.....Unless you're selling it.

ncrk
02-10-2008, 10:19 PM
nevermind guys....

projekt_s13
02-10-2008, 10:41 PM
for future reference 20 lbs of vacuum at idle is normal

Def
02-11-2008, 03:47 AM
Vacuum gauge on most imperial unit gauges is in-Hg(inches of mercury), and yes, -20 in-Hg at idle is normal for stock cams. For more bumpy cams you can get anywhere from -10 to -15 in-Hg.

ncrk
02-11-2008, 03:14 PM
but it says 20 pounds when im driving it too

stupid nissan
02-11-2008, 03:20 PM
is it 20 lbs of boost or is it vacuum they are to different things

corriganjoshua
02-11-2008, 03:24 PM
it says 20 ibs vac when your driving i take it, it reads that when you hit boost as well?

ncrk
02-11-2008, 03:24 PM
vaccum.........

ncrk
02-11-2008, 03:25 PM
yep...........

SHIFT_*grind*
02-11-2008, 03:26 PM
What vacuum source are you using for the boost gauge?

SoSideways
02-11-2008, 03:28 PM
Please use the correct terms when you refer to vacuum or boost, because you will confuse people if you don't.

Vacuum is measured in inHg (inches of mercury) on most imperial gauges, just like Def said.

Boost in measured in PSI (pounds per square inch) on most imperial gauges.

Please listen to Def as he is a helluvan engineer, and he knows what he's talking about.

20inHg of vacuum on a stock car is good.

I don't even get 20inHg. I get like 17 to 18 inHg.

g6civcx
02-11-2008, 04:29 PM
Take a picture of the gauge with the engine off and at idle. Do not try to take a picture and drive at the same time, or at least don't blame us if you crashed.

ncrk
02-11-2008, 05:46 PM
k, sorry guys im new at this
when its idle it sits at 0 ad when i get on the throttle it goes up to 10-20 inHg of vaccum
when the turbo kcks in it shows about 20inHg
so thats a good thing?
i thought i should be having press.

Kouki
02-11-2008, 05:52 PM
Either you got a bad gauge, or you tapped into the wrong spot for your vac source. You should be around 20inhg at idle, and under boost it should go up into boost psi. Is this a mechanical gauge? Where did you tap into for the vac source?

ncrk
02-11-2008, 05:56 PM
Either you got a bad gauge, or you tapped into the wrong spot for your vac source. You should be around 20inhg at idle, and under boost it should go up into boost psi. Is this a mechanical gauge? Where did you tap into for the vac source?
i tapped in right off of the blow off valve
im getting the feeling i did something stupid?

lazierhobo
02-11-2008, 06:11 PM
so as you come into boost, there is no change in the readings?

ncrk
02-11-2008, 06:14 PM
so as you come into boost, there is no change in the readings?
there is a cange
it goes up to 20

johngriff
02-11-2008, 06:16 PM
If it is -20 at WOT.

There is a big issue, no matter what the vacuum source is, even if it is N/A

ncrk
02-11-2008, 06:20 PM
is the blow off valve not the place to tap into the vaccum??

Kouki
02-11-2008, 06:21 PM
If it's an electrical gauge maybe you wired it backwards?

ncrk
02-11-2008, 06:24 PM
i think its mechanical cause it uses the nylon tube
but it might be electrical for all i know

bo2o
02-11-2008, 06:54 PM
take a picture.

it cant be right if your gettin nothing at idle.
take some pix of how you got your vac lines routed

2fast4y0u
02-11-2008, 08:00 PM
just follow this...


Where do the vaccum lines on an SR20DET go?

The vaccum diagram for the SR20DET is wonderfully simple. Thank god. There are only 3 vaccum lines that are absolutely necessary. Most mildly modified SR20's will have 4-6 depending on what extras are added on. Lets begin.

Throttle Body:
The throttle body has 3 vaccum sources coming off of it. Two above the throttle plate, and one below. The top left vaccum source is for the fuel pressure regulator. Also, if running a boost gauge (like you should), you will need to T off of this source to get the boost gauge signal. The top right vaccum source is for the Recirculating or Atmospheric Blow Off Valve. Lastly, the bottom left vaccum source is for the carbon canister. However, a lot of SR swaps will have this capped off because not having it isn't going to make us fail emissions. We fail anyways! The large hose above the throttle body that connects to the intercooler cold pipe is for the idle. Please hook it up; your SR will thank you.


Wastegate:
The wastegate gets it's signal off of the charge piping (aka Intercooler Piping). The stock piping has has a nipple on the cold side for the wastegate. Blitz and HKS front mount kits have a nipple on the hot side, and GReddy or custom intercooler kit will need to have a nipple welded in on the hotpipe (or somewhere else on the charge piping). If you are going to run any sort of boost controller, the boost controller needs to sit in the "middle" of this vaccum source. Meaning that you will need to have the nipple on the charge piping go to the "In" side on the boost controller, and the "Out" side needs to go the wastegate actuator. I don't have a boost controller on mine, thus I run a vaccum source directly from the charge piping to the wastegate.


Boost Solenoid:
This oddity sits on the ignitor chip plate. If you got a clip, yours was probably hooked up. Well... you don't need it when you swap it into your USDM chassis. Cap them off or take it completely off and do whatever you want with it. I suggest feeding it to your dog.



the website this was on is not going to availble anymore. so here it is.
Jay

Kouki
02-11-2008, 08:05 PM
Did you buy the gauge new? What gauge is it? Does the car seem to run fine, pull good up top, and idle smooth?

96Turbo
02-11-2008, 08:25 PM
i don't think you fully grasp the difference between vacuum and boost. When your engine is turned off, the gauge should be at 0. (atmospheric pressure). When you fire it up, it will go down (to the left, into vacuum). It is normal to be around 15-20 mmHg when idling. Most of the time while you're just cruising, it will be in vacuum, and begin to rise with slight throttle inputs. When you step on it, it should go past the 0, and into a new set of numbers (psi, to the right of the 0) which is boost.

Does your gauge stay below 0 the entire time?

that's sweet you live in garden grove...where is that? does it smell like lou dog inside your van?

Def
02-11-2008, 10:23 PM
^ Exactly, "zero" on your gauge corresponds to atmospheric pressure. Anything below that is "vacuum" or lower than atmospheric, while anything above is higher than atmospheric.

Units below are probably in-Hg of vacuum, while units above are probably PSI(pounds of pressure per square inch).

There is a BIG difference beyond "it goes to 20" when it is on either side of zero.


Also... what type/brand of gauge do you have?

I tried to tune a guy's KA that had too many ebay parts on it, and the boost gauge was basically a good random number generator. He thought it was cool as hell when it went to 35 psi when you went WOT at 2.5k RPM though...

SHIFT_*grind*
02-12-2008, 07:57 AM
When you say you tapped it "right off of the blow off valve," do you mean you just ran the hose directly from the gauge to the vacuum nipple on the BOV, without T'ing it off? You sound pretty clueless about all of this so I thought I would ask. If that's what you did, it's definitely wrong. The BOV isn't the best place to T off from, anyway.

Follow 2fast4you's instructions up there and as long as it's not broken, the gauge should work fine.

M374llic4
02-12-2008, 08:11 AM
If I am not mistaken you need to put a line from your intake manifold on that nipple on the bov to hold it shut under boost, otherwise when you hit boost the bov will just open and vent all your charge?

ncrk
02-12-2008, 09:12 AM
When you say you tapped it "right off of the blow off valve," do you mean you just ran the hose directly from the gauge to the vacuum nipple on the BOV, without T'ing it off? You sound pretty clueless about all of this so I thought I would ask. If that's what you did, it's definitely wrong. The BOV isn't the best place to T off from, anyway.

Follow 2fast4you's instructions up there and as long as it's not broken, the gauge should work fine.
i T'd it off, i know that much haha
and yeah im new at this whole thing
thanks for all the patience though