Mkai0

I am planning to install a Prosport mechanical boost gauge. However, I am not sure which vacuum source would be the best to tap into. Can anyone point out a good location I can use?

Weiboy718

iTrader: (10)

yes, remove your valve cover there's a vac line by each side of the throttle body. you can choose either side to tap into. this pic is tapped on the passenger side but there's one on the drivers side too. if you have the GTM kit tap it on the drivers side

Black Betty

iTrader: (60)

What forced induction do you have?

Mkai0

Oh yeah, forgot to mention that. GTM Stage one SC. I didn't plan on putting a boost gauge in at first, but since I'm only putting down 320whp with the pulley that should get me 400, I know I have a boost leak to find! The tribulations of aftermarket boost. Thanks for the help.

Weiboy718

iTrader: (10)

how's your idle? if you had major boost leak you car should be running like ****. did your tuner or whoever dyno your car plugged in a boost gauge?

Mkai0

The tuner did plug in a boost gauge and I was hitting 7.8 lbs with the 84mm Pulley that should get me 10-11 lbs on the HR motor. The same 84mm pulley on the VHR motor gives 8 lbs, but gets a little over 400whp, which I'm sure you know Weiboy. All tuning was done using Uprev and via the DynaPak. The funny thing about it is that I'm my torque peaks at 321 lbs, but the HP hits goes to about the 320-327 range then the powerband drops off in the upper rpms, which shouldn't be happening with and HR motor especially when SC'd. This leads me to believe there is a leak. Sam told me to tighten the bypass valve first to see if that's where the leak is. I'm gonna try and diagnose the problem next week. Just ready to get this thing running right!

Weiboy718

iTrader: (10)

that is weird! question...do you have that motordyne manifold installed?

Mkai0

No, I have ART pipes.

Mkai0

Weiboy, by any chance do you know what size vacuum line they are using in this picture?

mikelr

iTrader: (1)

If you are achieving 7.8 lbs of boost in the low to mid rpm range than you are not mysteriously developing a boost leak at the upper rpms. More than likely you are experiencing some sort of flow restriction on the intake which can't support the air demand at high rpm.
I experienced the exact same issue with my GTM stage 1 kit (I had one of the first if not THE first self install), the original intake tube did not flow well enough to make the advertised hp, after some reworking which included some porting and an extrude hone process the intake was up to the task. Maybe you some how got one of the original unmodified piece by mistake.
With a centrifugal style blower you should be producing more boost the faster you spin it which would still increase your boost level against a fixed "boost leak" especially as the VE of the engine decreases at the upper rpm range

Mkai0

mikelr,

I hope I'm not having restriction issues with my intake. My tuner somehow felt my custom exhaust was to blame. I don't think so because I have a custom 2.25 inch exhaust with X-pipe and Art pipes and dynoed 261 whp on a Dynojet prior to going FI. I'm gonna first tighten the bypass valve to see if I'm losing my power there. If that doesn't fix it I'm going to get a boost leak test done.

Weiboy718

iTrader: (10)

Dang, I forgot what size it is. GTM manual doesn't say either, I just checked.

Per my friends with superchargers on their 350z they said with test pipes you may lose some boost but it's just weird how you only made 330ish whp. Do you have the turbosmart bypass valve? FYI, You can reach the bypass valve from up top or at least I can. Hopefully you don't have very big arms and hands.

Mkai0

I have the turbosmart, and I cannot reach it from the top. I'll be removing the bumper to tomorrow so I can reach it.

Weiboy718

iTrader: (10)

try it getting it from your undertray.

I highly doubt you're leaking boost pressure otherwise you would've never made 7.8psi of boost. Is your car running normal?

Mkai0

Its running normal with a lot more torque, 321 lbs to be exact. My boost is tapering off in the upper RPMS which is evident by my power curve dropping. This leads me to believe there may be a boost leak. I'll try reaching the bypass from the bottom tomorrow.