Is a boost spike of 16 to 11psi acceptable?

[RandyJr]

Man, the search function brings up everything but what I'm looking for.
Okay, I 've noticed that about in any gear, my boost will jump to 16 and go down all the way to about 11 and hold, maybe 10. Is that normal or is there something wrong? Any advice?

 

[psychlow]

Sounds a little high... is the car stock?

I would check all of the vacuum lines between the BCS/turbo/wastegate actuator for leaks or cracks...

Iif that doesn't help you may want to try bypassing the BCS (just run a vacuum line from the compressor outlet to the wastegate actuator) to see if that fixes it.

 

[midnght]

No, a 5psi spike is not acceptable. You might want to check a few hoses. See if there are any leaks or kinks. You might also want to check your wastegate and see if it is opening correctly.


Sometimes MBC that use the bleeder type function do not have a hole big enough to dispense the air to help keep the boost from building in excess before it "bleeds" off.

 

[RandyJr]

I have a MBC and boost gauge with all the vacuum lines removed. I have the boost turned up, I was wondering if it's normal for the boost to go down 5 psi after spiking. I'll recheck all my hoses but I'm sure everything is good.

 

[psychlow]

That was worth mentioning.

Also, make sure your vacuum lines between the boost source, the MBC, and the wastegate aren't too long. If they are, it might take longer for the pressure to hit the wastegate actuator because of the longer path.

 

[RandyJr]

Thanks psychlow, that was the problem. A friend I called an hour ago told me to check and see if I had a long hose on the MBC. I knew I did so I went and cut about a foot off the hose and it spikes about 1-2psi now. Thanks.

 

[psychlow]

Anytime, bud. Glad you got it fixed.

 

[BMWHATR]

Dude I am having the same problem. But my boost Jumps to 20PSI on T-25 WTF?
and the car sound lot louder. My house is about 3" from the factory one.(factory + MBC= 3" longer then OEM) What do you guys think i sould do?

Its not so bad in 1St gear but 2nd i get 20PSI that kind of freeks me out. and its not like its for a sec its like for 3 sec. till it goes back down to 13psi

 

[psychlow]

If I were having the problems you mentioned, I would replace all of the factory line with new line if you haven't already. Make sure your MBC is hooked up correctly, meaning the boost source line goes into the longer end of the T-shaped MBC (directly across from the set-nut), and the wastegate is hooked up to the short end.

If you have it backwards, that'll produce the symptoms you described. The wastegate won't get a signal, and the MBC won't work at all. Boost will just drop off when the T-25 runs out of steam.