boost loss

[ken06]

I have a hallman pro boost controller with the pressure t-d off a greddy rs. When I'm accelerating at WOT the boost will hit 14psi then drop to 11psi at about 3k or so and hold steady. It almost seems that my boost controller opens up but stays open giving me stock boost. Any ideas? Also what size are the vacuum lines because mine are multi colored right now , I think they are 4mm but i'm not sure.

 

[lil corb]

What do you have your MBC set at 14psi or 11psi because if it's at 11psi it just sounds like the MBC is spiking. Is the connection to the wastegate too long?

 

[crunchymilk]

yep, definitely sounds like your boost is actually at 11, but spikes to 14

 

[luvmygst]

Hi Im a T-25 i will never hold 14psi till redline!!!! Seriously it sounds like the small factory turbo just cant keep up. I know mine couldnt when I still had it on my car, I had the same problem, the boost just could not keep up with the motor. Time for a 14b

 

[ken06]

Ok thanks for the help i'll see what I can do to shorten the line cause now that I think about it it is definetly boost spike, I have the mbc mounted on one of the screws that attach the passenger side engine fan to the radiator, on the top left right by the mas, so if I dont move the controller I'm sure I can shorten the line.

 

[MrBoxx]

Get your boost pressure source from the T25 compressor nipple, not the BOV line. Leave the BOV line alone. You're in essence creating a boost leak in front of the BOV and possibly delaying it's opening. That's not a good thing. There have been several people recently who have moved their MBC pressure source to the compressor housing or the LICP nipple on a hard pipe and have had the majority of their problems disappear.

Here's what oldman has to say about it:

Taking the pressure source from the j-pipe fitting has many benefits.

1. The main reason why alot of mbc instructions and some tech articles suggests to tap from the BOV line is because it's connected to the intake manifold, the argument is that this is more accurate because it's the same pressure the engine sees. In reality this is a non issue because the boost gauge is tap to the intake manifold no matter where you tap your mbc so there is no advantage in tapping the bov/manifold pressure as previously thought.

2. The proper functioning (opening and closing) of the bov depends greatly on the accuracy of the pressure in the vacuum hose you're thinking of tapping on or off boost so it's best to leave it connected directly to the manifold without any interference.

3. Tapping off the compressor/j-pipe offers the shortest vacuum hose route which greatly reduces the chance of boost spike.

4. In the case of boost leaks, tapping off the compressor/j-pipe will help prevent over boosting the turbo.

5. Hooking up a bleeder type mbc like the TurboXS standard mbc to the bov line will result in a vacuum leak as well as affect the working of the BOV.

-as originally posted by oldman

And here's a graphical representation using a TurboXS hi-performance MBC that I drew up in my spare time:

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And do a boost leak test. Don't just assume that because your hose clamps are tight that you aren't leaking boost from anywhere.