Okay, so I have a boosted B1 with ARP head studs and ARP rod studs. I rebuilt the motor with all OEM parts before boosting it. The turbo kit is a Go-Autoworks kit. I have their intercooler and piping, a Garrett 60-1 T3/T4 hybrid 550hp turbo, Tial wastegate, Aeromotive 340 pump, AEM fuel rail, AEM fuel pressure regulator and ID 1,000cc injectors.

The car made 335 hp @ 11.6 lbs of boost and 356 hp @ 12.4 lbs of boost.

I’m running a cheap Glowshift boost gauge, but it seems to be doing (or at least has been doing) the job.

I recently rebuilt the turbo myself with a G-Pop Shop kit, and took the shaft and wheels to a reputable turbo shop around me to be cleaned and balanced. After breaking the rebuild in, I noticed that no matter how high I crank my MBC, the car won’t hold over 8 lbs of boost. I have boost leak tested and I can’t seem to find any leaks, but when I’m boost leak testing, the system won’t hold over 10 lbs of boost, as far as my boost gauge shows me. I’ve sprayed everything with soapy water and I’m not seeing bubbles anywhere.

I have a Turbosmart MBC with the correct line hooked up to the wastegate, with the other line hooked up to a nipple that I welded in the intercooler pipe coming out of the turbo. Like I said above, no matter how high I crank the MBC, the boost gauge won’t read above 8 lbs of boost, and it doesn’t feel like it’s boosting more than 8 lbs either. I can adjust it to make less than 8 lbs, but nothing over 8 lbs.

I’m not sure if my wastegate is stuck shut or stuck open, but I’m wondering if this is the culprit. How would I go about checking this?

If it’s not the wastegate, what else should I go about checking?

Thanks in advance!

This is actually a brand new MBC. Like legitimately less than 100 miles on it - probably less than 50. How do I check the wastegate? I had it off a few days ago and everything moved by hand as it should.

I took the wastegate off of the manifold and it was completely shut. With some force of my fingers, I pushed the piston in against the pressure of the spring. It opened and sprung closed. Assuming this would mean the wastegate is working properly. I had the wastegate open, and the seal to the diaphragm was flattened out in of section, but I unflattened it and put some Hondabond on it to reseal it. I know this is the cheap way around it - just don’t really feel like buying a new wastegate at this time.

I’m not quite understanding what you’re saying. There’s 2 nipples on the MBC - one of which goes to the wastegate, which is at the manifold, and the other goes to a vacuum port, which I have it on the intercooler pipe coming out of the turbo.

I’ve had this turbo kit on a car that I used to drag race, with the MBC setup the same as I have it now, pushing 30+ lbs of boost, running in the 10 seconds.

And I have the red wastegate spring. I’m not sure what lb spring that is, but it held the 30+ lbs of boost that I threw at it before.

most eveyone only uses vacuum lines directly off the manifold because of boost drop from intercooler. The manifold is the most accurate reading you can get.

yep, that’s why I was hinting that it might need to be moved

Maybe I will go ahead and order a new diaphragm. I’m just not understanding why the Hondabond wouldn’t seal it up.

You said that you get boost drop from the intercooler. The pipe coming out of the turbo is pre-intercooler. And when you say ‘manifold’ are you referring to the intake manifold? Because if so, that’s post-intercooler, so wouldn’t I be seeing the boost drop?

pre intercooler in my mind would be between the turbo and intercooler. Boost levels are always higher on the turbo side of the intercooler. Pre mean before and post would refer to after, or so I thought. Lol

Well, yes, the nipple on my intercooler piping is on the pipe coming out of the turbo, going into the intercooler, so it would be pre-intercooler. So from what you’re saying, this should be okay then, right? It goes turbo ->pipe->intercooler->pipe->intake manifold

no. You need your wastegate to read what the motor sees. The wastegate could see a higher boost pressure than the boost gauge or ECU and open prematurely and could cause some floating as the piping try’s to equalize. All lines should be connected to the intake manifold and the connection on the turbo should be plugged. Depending on the size and flow of your intercooler you might not see a big difference, but in a case of fast spool up, you might have the wastegate prematurely open if you get some spike between the turbo and intercooler. I’ve seen boost levels bounce around before because of the use the turbo connection. Best way to think about is like a tire out of balance, at certain speeds it can get way out of control

That was a really good way to explain it. Looks like I’ll be ordering a new diaphragm tomorrow!

Understood. So here’s another question then. I’ve heard some bad things about teeing into things. I don’t have the factory PCV system on the motor, as I have breather box running to 4 different places on the motor. I have the BOV line running into the nipple on the intake manifold where the PCV line would originally go. Would it be alright to tee the MBC line into this line? This might be a dumb idea, but I’m gonna ask about it anyways - what if I drilled the intake manifold and tapped it and threaded a barbed fitting into it (given there’s enough material to thread it) for a vacuum source for the MBC?

only thing I have against drilling and tapping would be if the intake is still attached, the smallest sliver shaving can get stuck under a valve.... trust me, it happened to me and I had to pull the head off only to find a tiny metal shaving that come off a intercooler pipe. It took 2 secs to knock off the shaving and 5 hours to remove the head buy and put a new head gasket on and pay the machine shop to pressure test the head. A vacuum manifold always sounds better to me lol

I think I’m going to go ahead and drill and tap the manifold.

I’m pretty meticulous when it comes to things like this, as I’m a CNC machinist. I’m gonna drill and tap the manifold. If I do get shavings in the engine somehow, I can have the head off in an hour. Fortunately, I know the B series like the back of my hand.

I don’t think the wastegate is fine though. The diaphragm is flattened out in 2 separate places, and oddly enough, I figured out that I had a 5 lb spring in the wastegate. I say this is odd because I’ve used this exact turbo setup in the past, pushing 30+ lbs of boost, running 10.8 second quarter mile passes.

I ordered a new diaphragm and a 10 lb spring today. Should have them tomorrow or Thursday.

I think you replied to the wrong person.... I agreed 100% with you in my post

Not a problem! The diaphragm and new spring just got here. I’m in the process of getting everything back together right now!