Ok, I feel a bit silly about this, but I really don't have any prior experience with SCs or boost gauges...

I've finished my install of a Powerdyne SC and some gauges (boost and fuel pressure). Took it out for a "test run" and was very impressed with the power gains. Going for dyno-tuning on Tuesday. But, something is not right with my boost gauge!

I thought I just needed to tap into any ol' vacuum source on the car, and I had an open vacuum fitting on my intake manifold (I can't recall what was there -- emmissions something-or-other most likely). It is the small fitting right next to the power brake vacuum fitting. So, I connected my gauge to it. Well, instead of showing the 6lbs of boost I expected, when I start the car it slowly climbs (descends) to about 12 lbs of vacuum. The SC is definitely working as I can't believe the additional power I'm getting, so obviously something is wrong with the gauge set-up.

Any help would be greatly appreciated!

Thanks,
Mark

 

Emmm......you're not going to have boost at idle. It will always be in vacuum at idle. The throttle plates are closed....no way for any decent amount of air to get past them to produce boost.

You won't get boost until you punch the gas to open up the throttle plates to actually allow boost to start building through increasing the blower's RPMs.

You're probably not going to hit 6 psi of boost until 4,000 RPM's or higher anyway.

 

Oh yeah... duh! I didn't think of that!

I took it out for a quick run but didn't watch the gauge closely to see where it was reading as I increased revs. I did sit in my driveway, revved it to around 5,000, and held it for a few seconds -- the gauge came up a little but was still showing a vacuum.

Maybe the line is pinched somewhere? So it isn't getting quick readings?

Bottom line is I did connect it properly, I guess.

Thanks,
Mark

 

It's probably hooked up OK.

It's still not going to really get into boost without putting a load on the engine (while you're driving). Simply revving it in the driveway will only produce momentary bursts of boost, and only the instant you jam the pedal down (at least in my experience).

When I had my 6 psi pulley on, I'd only get a reading of 1-2 psi while jamming the gas without a load.....again, only momentarily, for a split second. With my current 12 psi pulley, it'll jump to 6 psi or so without a load.

Watch it while you're driving, I would almost guarantee it'll show the correct boost under load. If it doesn't, check to make sure your gauge's line didn't kink anywhere....and make sure your bypass valve isn't stuck open (if your system uses a bypass valve).

 

ok, thanks.

Mark

 

You gotta watch it at near redline while driving it. Until you rap it up, you aren't gonna see positive boost. You can't do it by free revving in your driveway. Your blower will hate you for that anyway!

Mike M