legacycentral bbs

Hey everyone, I just finished installing a boost gauge in my '93 Turbo Legacy Sedan. I thought i'd write up a little thread on how the install went.

First, the gauge. I went to GI Joes in Lynnwood, WA and bought a cheap Sunpro boost gauge for $24.99.

First step was finding a vacuum line to tap. Here you can see I chose a line right behind the intake and throttle body (look for the little T with the clear wire coming off of it). The vacuum line runs down to the firewall, and through the grommet right behind the brake pedal.




After that, we needed to find a place to mount the gauge. I chose the door, because the piece it is screwed to is possibly the smallest interior piece in the car

I screwed the gauge into the interior piece, and then ran the wires and vacuum hose down through the seam in the door panel. I covered the wires and back of the gauge with electrical tape in hopes of hiding the wires a bit more.

I ran the wires down to the floorboard. I grounded it to a random bolt I found down there, then ran a power wire over and tapped into the Lighter Light-bulb.

Anyway, here are the pics. If you have any questions or comments, feel free to drop me a line!

That really isn't the place that I would T into for Vac/Boost readings. You should T into the line to the pressure sensor that comes off the #1 intake manifold. Like this:




Besides that though it looks pretty good.

The biggest problem was finding a hose that we had a properly sized T for. Stupid vacuum hoses all seemed to be slightly different sizes!

Why is that location better than the one I used?

interesting place to mount the guage, i just put mine in an a-pillar mount and shoved them between the dash and the a-pillar till i get time to screw it in. Looks like it belongs there tho.

I'm searching for an A Pillar pod to mount it with, but for now, that was the piece of interior that I didnt mind screwing in to. Doesnt look so bad either.

Well, the line off of the #1 Runner is used as the stock boost control manifold pressure line.

What your gauge would read, is exactly the same pressure that the computers stock boost control sees.

The line you tapped, is the Diverter Valve pressure reference line. The stock DV opens fully based on differences between that inlet line, and the turbo-to-throttlebody pipe. Since it's a manifold pressure line, it WILL work for what you want to do, but a leak in that line, would be problematic (the DV would not fully open). I had that same boost gauge (it's unreliable, btw) for about 10 minutes, and it leaked like a sumbitch. I wouldn't want that to be leaking on the DV return line, but that's just me.

I t'd mine in right off of the #1 Runner. And I spent a few bucks more and got a good boost gauge.

syphon - Cool writeup.

For hose sizes, look at my vacuum diagram: http://www.graphics.cornell.edu/~v/vacuum/

The hose you tapped into is the one controlling the blowoff valve, and is very close to 7/32". Like Phil says, a leak in that hose would cause some trouble -- not only could it prevent the valve from opening soon enough, but if it were a big enough leak it could also cause the valve to leak boost. I don't know if a tee that size is big enough to cause such a leak though.

The one most people (including Phil) tap into seems to be the one on the front passenger side intake runner, and is close to 1/8".

Phil - The gauge body itself leaked? That's weird, and surprises me. I think the particular unit you got might have been defective in that case... a pressure gauge shouldn't be able to leak, since that throws off pressure readings. More commonly the fittings leak if not fastened correctly.

A quick reply with a picture of the gauge at night..

I'm considering moving that vacuum hose to the one suggested, but I dont know if the existing hose is long enough to reach there, and re-routing a new hose would be a PITA. Anyone know of a good store that carries lots of vacuum fittings?

Most auto parts stores I've been to have a wide selection of random little plastic vacuum fittings. If they don't have them out on a shelf or something try asking at the counter; some of them keep them in a drawer.

Hardware stores typically have 'em too.

You wouldn't have to re-route the whole thing; just get a little union fitting and connect the hose you have now to a new length of 1/8" hose that routes along the back of the firewall and then down to the hose entering the driver side of the pressure exchange solenoid. Tee off it right there with an 1/8" tee.

The other problem is that the hose that came with the boost gauge is a shitty little nylon hose, and it's TINY. I worry about finding some sort of union that will fit it AND a larger vacuum hose.

Usually rubber vacuum hose fits right over that nylon hose. The nylon hose that came with my gauge had an outer diameter of 1/8".

Have you tried seeing if you can just connect the nylon line directly to 1/8" rubber vacuum hose?

Vikash - The compression fittings they included did not compress properly. You could feel the air coming from it.

That "shitty little nylon hose" is what comes with most gauges, including my Autometer gauge. I ran mine through a rubber vacuum hose to protect it (following Matt's recomendation). I've never had a problem.

You slid the ferrule on the nylon tube and torqued the nut down, and it leaked? If there was a pipe thread connection also, you had Teflon tape on it, right?

That's kind of ghetto that it leaked.

What I did when I first got my gauge before I understood how the compression fittings worked was to
just stick a short piece of 1/4" vacuum hose over the 1/8" NPT fitting and held it with a ziptie. I used an adapter to connect that to a piece of 1/8" hose that slid right over the nylon tubing. It worked fine for me.

window glare = yuk!

finish leaves to be desired, but good for you on general procedure.

Vikash - Yea, I used the compression fitting correctly, and it still leaked.

I think it was partially due to the fact that the whole thing was old, and the nylon hose was brittle. I snapped a peice of it off with my bare hands in one bend.

Oh, I think that'd definitely have something to do with it... Compression fittings are based on the idea of the tube material plastically deforming.

Indeed. I didn't even look at the thing when I took it off. The gauge was there for like a week before I got fed up with it, and got a real gauge.

Sorry to bump a fairly old thread...

I don't know what people are talking about when they say "inaccurate boost gauge" or claiming that where I tapped the vaccum line is bad. This gauge is as cheap as they come ($24.99 at GI Joes) and it's been dead-on with vrg3's scantool.

I installed an MBC last night and we did some tuning, and I found the gauge to display exactly what the scantool displayed. Perhaps I just lucked out with a good unit.

so what line should i tap into in that diagram?