dachmo

I just installed an autometer phantom boost gauge on my SC tC. At Idle, I'm reading 20-25mg Hg..... The thing is that it stays in vacuum, between 0-15mg Hg, while im at part throttle, and only goes into boost at WOT. I have the NST 9.5 psi pully and I only saw about 8psi....

What could the problem be?

I thought the car would be in boost at part throttle too.

could it be as simple as a leak in the boost gauge fittings?

Thanks

- Dante

WeDriveScions

Looks IDENTICAL to my setup.... 20-25 at idle and then climbs a bit and starting at ~2600, climbs past 0 and then up to 6 (until my WG dumps, then just stays at 6) with the S/C, I'd think you'd get a linear transition up through the RPM range.

That's with an Autopower manual boost gauge....

dachmo

It is a linear transition, but it's only up to about 8psi and it doesn't build boost under part throttle...... even though I can hear the SC spooling.

If I accelerate at about 50% throttle, I'l build about 1-2psi throughout the entire RPM Range from about 2500+rpm

Is that normal?

- Dante

yamaha16bw

Well I'm turbo and that sounds just like mine. I can hear the turbo spool but its still in VAC. I would worry about it. You should right at -20 at idle. I get about -24ish when I let off the gas while moving.

dachmo

did you really mean that???

yamaha16bw

Sorry, I meant to say wouldnt worry about it. My bad

06scionsc

You have a few possiblities. One you have a vaccum leak causing incorrect readings. Two you have not switched out the stock bypass valve and have boost leak. Three the gauge has a leak in the line somewhere. Four you have a belt slip problem. All of these are possiblities. As for only seeing 1-2lbs of boost. That is pretty normal. I see about 2.5 lbs until about 5k then it will start to go higher. I only see 9.5 right at redline.

OuterHeaven

With the supercharger boost is a relationship between RPM and how much the throttle is open. Even at partial throttle I think the bypass valve is being used so therefore you will not get as much air into the engine. You should only see 9.5 psi at Max rpm while at WOT.

WeDriveScions

^ Good Answer from a S/C guy!

3min3m2

yeah thats the only draw back to it...but as your amount of vaccum increases, that means your boost is building....just hasnt ecame a positive number

Joe_Dezod

I'd say your setup is normal. It depends on where you tap your vacuum line. OuterHeaven is right though, the bypass valve is doing that due to your engine's load and throttle position. When you open it up, the TB opens and all the air can finally rush in, at the boost it needs to be at. You MAY have a small boost leak somewhere or a belt slip if you're actually supposed to hit the 9.5. Sometimes the gauges are a little off too so keep that in mind.

Nick06tC

I will put my experience in.
I am running the 9.5pulley as well and have an autometer boost gauge. EVERYTHING IS FINE WITH YOUR SETUP!! You will only see boost if you are pushing it hard. You can easily drive the car a few hundred miles without ever seeing boost. Its awesome because it helps with gas milage. No boost, no extra gas!!

The way mine seams to be. No matter how low the RPMS are, if I floor it it will hit about 2 psi instantly, then build from there and hit 9.5 right before shifting.
Dont worry everything is fine!

Nick06tC

oh just saw you arent seeing the full 9.5psi.
I would say, the gauge is off, or you have a boost leak, or your belt is slipping.

Did you change the belt with the pulley?

OuterHeaven

Are you still using the stock bypass valve with the 9.5psi pulley?? That could be part of your problem.

Mase77

I know on my car (Ion Redline) you won't see boost unless you hammer it. It''s simply as stated above, TP not open enough. BTW I see 10psi instantly when I hammer it at 3000rpm and 20psi at 7000rpm

IceNine

If you are using the stock BPV *OR* the 110 Sport, you'll leak boost.

Been there, Done that, Wrote the 'for dummies' book.

Get the Forge, put the stiffest spring in, use the 2 shims, install it, problem solved.

dachmo

damn.... I thought I'd be fine with the 110sport....

I'm definately only seeing 8psi at redline so I think maybe it's time for anew BPV...

Thanks

IceNine

I've heard the Bosch is only good for up to around 7lb max (so 8 isn't much of a stretch). Mine saw 6-8lb max, but once I swapped it for the forge it was a full 9.5lb at redline (at least, once I put in the stiffest spring + shims).