Hey all,

This past weekend I installed my Forge UNOS MBC.. Anyhow, I have one line from the MBC going to the turbo outlet nipple, and the other going to the wastegate. I originally had it tee'd into the BOV line, but recinsidered after this problem started. Anyway ever since I installed the MBC the car has been boosting fine(20 psi till the tune). When the car goes into boost it holds 20 all the way to 5500 or so rpm then it will start leaking boost and fall back to 15 os so psi. If I start in 1st gear it will leak right away and leak as soon as it hits boost in any gear, whereas if I start a pull in 4th gear it will go right to 20 and hold just fine untill 5500 rpm or so as stated above. I've had the car apart 3-4 times now re-checking everything, I have zipties on the nipple and wastegate now, doesn't seem to be leaking there however. I also have 2 zipties on the MBC now. I also put t-bolt clamps on but it still is leaking. Why would it hold on a pull till higher rpms, but if I go through the gears it leaks as soon as I hit boost? Anyone else ever have a problem like this? I noticed the MBC has a bleed off hole and thought maybe it needs a stiffer spring put in, but figured I would ask here before I proceed further.

Thanks!

 

Has anyone had a problem like this? Is this serious? Your MBC is not "leaking to 15psi." It's called boost taper. You've honestly never heard of boost taper nor seen it discussed?

Lower gears = less load = less peak boost + sooner taper + more taper
Higher gears = more load = more peak boost + later taper + less taper

 

so ok how do u maintain a constant boost through all rpms?

 

No it holds fine, then you can hear a high pitch whistle from under the hood.. It definitely is not taper, it holds 20 then bam it falls to 15, I know what taper looks like, and this definitely isnt it. It sounds like it is right at the firewall, but I have t bolts on everything but the connections to the intercooler.

 

Electronic boost controller

 

Maybe the seals in your BOV are going bad, or are all dried up from underhood temps.

 

Also, the stock boost solenoid would hold 19 psi to redline on a 4th gear pull before anything was touched.. I know on my old DSM I could blow apart a throttle body gasket when boosting too much, is that a common problem on the Evo?

 

The car is brand new. It held 19psi fine on the stock setup, I dont understand why 1 psi more on an MBC would make it go haywire + the addition of t bolt clamps.

 

I never heard of it being a common problem. I would do a boost leak test. If you were boosting to 26 psi, you may have opened up a leak somewhere.

 

Is there any way to get the inlet pipe off of the turbo without disturbing any of the other piping? I know I had a hell of a time putting the MBC in with taking the fan out and IC pipes off.. I would like to leave everything as it is to test, but I think it would be almost impossible to get that tube off without removing something.

 

Sure you can. It's a tight squeeze though. Pain in the butt to get the screw driver on it but it can be done. Check to see if any of your pipes slid partly back towards the end of the i/c pipes. I had a guy who's pipes were about to pop off and they were leaking like crazy. Wait, you took the fan out? You don't need to do that.

 

maybe you have a problem with your blow off valve did you install it the correct way when putting the mbc?

 

I didnt remove the BOV.. All the pipes are tight as can be as they have t bolts and the pipes coming out of the IC look fine..

 

I would still do a boost leak test. It may look fine and leak at the same time. You can try removing your boost controller and hook up the stock boost selanoid to see if it has anything to do with the boost controller.

 

Oh, you didn't give those details.

You have the Warrtalon Intake Snorkel Syndrome, and Bat-talon is here to save you. My crew of saved Gotham City Residents:

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