Unsolved Boost Mystery

[wcxbp240]

I disconnected the vacuum line that attaches the wastegate to my MBC and something amazing happened...I started boosting 15+ pounds with the stock T25 turbo. Besides the obvious vacuum leak sound, my BOV is now making a sound like a rattle snake (flutter?) when it blows off at lower boost levels. Is this a safe/wise thing to do? If so, can I cap off the open end of the MBC to get rid of the vacuum leak and still get the same results? I've never been happier with the performance of my car, but I don't want to damage the engine or the turbo. Any help would be appreciated.

[Warped]

your bacically destroying your turbo with anything over 13-14psi to it it looses its efficiency and all you doing is heat soaking you ic and damaging your turbo + your fuel system if stock can't handle over the 13-14psi mark and your really leaning out your motor probably causing damage

[SpeedRacer1]

You are running an open wastegate. This is unsafe because the turbo runs on limitless boost until it blows up based on throttle position.

[highmilehatch]

Jesus. You disconnected the vacuum line from your wastegate. Now your wastegate has no idea when to open. You are overboosting. If you don't want to ruin your engine, I suggest putting that line back on. No it is not safe.

[wcxbp240]

Damn it...I guess its back to stock 7 psi. This was too good to be true. Thanks for the help.

[9240sx]

So why cant you boost higher then stock now????You said you have a MBC.So whats the problem

[wcxbp240]

I don't know what the deal is with my MBC...I have turned that thing every which way and it always boosts 7 psi. Also, I am not 100% sure that it is hooked up properly. From searching this site I found out that I need to upgrade my fuel pump in order to boost more. But for now I am going to try a new O2 housing, down pipe, and test pipe (all 3 inches). Any suggestions/recommendations for my fuel pump uprade?

[9240sx]

Walbro 255lph works very good,Iv had mine for 4years with no problems at all..If you have alittle more money to spend,You can always get a Tomie,or mod the a z32 TT or Skyline pump to work..But you sould just get the Walbro 255..For cost and install reasons.

[wcxbp240]

How much of an increase should I expect by upgrading to the 255 lph pump? Do you think that my new exhaust options will increase boost? Searching around your site and talking to other SR owners, the consensus is about a 3 psi gain over stock. I am already 3 inches from the cat back.

[nzmoman]

you may want to think about a bigger intercooler before turning up the wick.

you seem really anxious, but you have to be careful and take your time or the next thing you know youll be spending $ on another motor.

your exhaust system will free up the turbo, but it is not going to allow you to go boost crazy, it will mostly let the turbo spool faster, and a tad higher, but you should really check out a decent front mount unit and exhuast system.

But take your time and be patient.

[wcxbp240]

I already have a FMIC installed (should I be seing more boost?)...I'm just getting aggravated with my car's inability to boost. When I first got the car 7 psi was incredible, but now....not so much anymore. I just ordered the fuel pump last night and my exhaust will be 3 inches from the turbo back on Friday. Sorry to complain, just frustrated.

[dustyk]

If you MBC isnt working, you either dont have it plumbed in correctly or its defective. An MBC is just a valve that limits the amount of air that goes to the wastegate or actuator, I really dont see how it can be broken. How do you have the MBC plumbed in?

[wcxbp240]

The vacuum line from the manifold is "T'd" off with one hose going to the BOV and the other going to the MBC. That line exits the MBC and goes directly to the wastegate.

[boost_creep]

you should keep the bov line on its own from the manifold.the input for the mbc should be off a chargepipe,then to the wastegate.i think it works better,and safer this way.

[wcxbp240]

I cannot find a nipple on my charge pipe to connect the line to. Do you have any pictures of what I am looking for? Sorry man, I am a turbo noob.

[Blown240sx]

Obviously.... YOur lucky you didnt blow your turbo up or worse your motor.Next tiem ask before doing something.

You shoul have 3 nipples on the Intake Manifold. If they are all used then get a nipple welded on your Front Mount piping. You should be able to turn the boost controller clockwise till it stops which should be closed then twist it out some and test run it in 3rd gear. Adjust from there.

If its not working try flipping the hosing to the other nipples on the MBC.

[wcxbp240]

Yeah, I guess I lucked out. I was never over 15 psi for a few seconds during the 10 minutes I had the vacuum line disconnected. My manifold only has 2 nipples...One of them is going to the BOV and the other to the Boost gauge. Help the noob please...

[Blown240sx]

go to a weld shop and have them weld you a nipple on your hot pipe of your front mount turbo piping.

[drifter_for_life06]

im going to be an a$$

everything you have asked thus far.....has been answered numerous times