Need the experts on this (MBC)

[95RedGST]

Ok I fixed the MBC...It holds at 15 psi but the only thing is it spikes at 20 psi than goes to 15 psi and holds again. Im not getting why it spikes.

 

[Bohrn]

someone please answer this so we all can know. I think it is a flow issue, where not enough pressure goes to the wastegate, but I am not sure either.

 

[turboholic]

-Make sure the brass orifice is still in the hose b4 the "T" from the air filter in the circled area. .

 

[Bohrn]

on a manual boost controller??

I just have vacuum hose,as I think most people do. In the factory boost controller, it is t ed in like that. How are we supposed to set up a MBC?

 

[95RedGST]

I was told ALL MBCS spike..and i cant really stop it.

 

[turboholic]

-I have never use mbc (have profecB) but was told that the amount of spike you get is corresponse to the distance of the mbc and the boost source, ie: if the mbc is mount in the cab, you'll get tons of spike.

 

[95RedGST]

Soo if I shorten the vacume line from the wastegate to the MBC, itl make it minimal right?

 

[95RedGST]

Shorten the vacume lien to the turbo nipple to the MBC or from the wastegate to the MBC?

 

[97GSTURBO]

I had the same prob, I had the line running down out of the way so I couldn't see it and it'd spike 5 psi above what it was set for, I shortened the line by about 6 inches and that got the spike down to only 1-2 psi above what it was set for. Good luck!

 

[95RedGST]

Wastegate line or the turbo nipple line, what vac line?

 

[cucumber]

Eric, I've told you what you need to do buddy.

 

[GRNDSM]

MBCs can spike for two reasons:

-Bad design/intallation
-VERY quick spooling turbo (like T25), that overshoots the preset boost level.

In ether case, it is not always a bad thing. You get higher boost at lower RPMs, where it is not as dangerous to run high boost.

Leon
RR

 

[jim97gst]

In ether case, it is not always a bad thing. You get higher boost at lower RPMs, where it is not as dangerous to run high boost.

I'm running a T25 with a 3" O2 eliminator downpipe, UICP and 1G BOV. I'm getting spike as high as 19 PSI at low RPMs and then it drops to 15-16 PSI. I'm not running a boost controller and don't want to because I don't want to be in the street mod class for autocross. I logged it and I'm getting ignition retard as low as 2-3 Deg during the spike so I'm likely getting detontation, right? Am I going to have to bite the bullet and get a boost controller? Here's a log of a 2nd/3rd gear pull:

time,RPM,timing,TPS,O2

01:15.05,736.0,9.0,1.96,0.18
01:15.73,996.0,3.0,1.96,0.26
01:16.43,1608.0,3.0,13.36,0.06
01:17.12,1852.0,26.0,15.32,0.08
01:17.80,2104.0,22.0,23.97,0.36
01:18.50,2428.0,24.0,29.47,0.3
01:19.19,2836.0,22.0,35.76,0.7
01:19.87,3428.0,4.0,52.26,0.94
01:20.55,4040.0,2.0 ,98.23,0.96
01:21.26,4680.0,3.0 ,98.23,0.96
01:21.95,5348.0,5.0 ,98.23,0.96
01:22.63,5952.0,10.0,98.23,0.96
01:23.33,6496.0,16.0,98.23,0.96
01:24.01,6508.0,18.0,98.23,0.98
01:24.70,4676.0,39.0,98.23,0.94
01:25.38,5056.0,9.0,98.23,0.96
01:26.08,5384.0,11.0,98.23,0.96
01:26.77,5688.0,15.0,98.23,0.96
01:27.80,6072.0,19.0,98.23,0.96
01:28.50,5460.0,21.0,1.18,0.72
01:29.19,3940.0,35.0,1.18,0.7

Is there some way to control this other than a boost controller?

Thanks

 

[jim97gst]

In ether case, it is not always a bad thing. You get higher boost at lower RPMs, where it is not as dangerous to run high boost.

I'm running a T25 with a 3" O2 eliminator downpipe, UICP and 1G BOV. I'm getting spike as high as 19 PSI at low RPMs and then it drops to 15-16 PSI. I'm not running a boost controller and don't want to because I don't want to be in the street mod class for autocross. I logged it and I'm getting ignition retard as low as 2-3 Deg during the spike so I'm likely getting detontation, right? Am I going to have to bite the bullet and get a boost controller? Is there some other way to control this?Here's a log:

time,RPM,timing,TPS,O2

01:15.05,736.0,9.0,1.96,0.18
01:15.73,996.0,3.0,1.96,0.26
01:16.43,1608.0,3.0,13.36,0.06
01:17.12,1852.0,26.0,15.32,0.08
01:17.80,2104.0,22.0,23.97,0.36
01:18.50,2428.0,24.0,29.47,0.3
01:19.19,2836.0,22.0,35.76,0.7
01:19.87,3428.0,4.0,52.26,0.94
01:20.55,4040.0,2.0 ,98.23,0.96
01:21.26,4680.0,3.0 ,98.23,0.96
01:21.95,5348.0,5.0 ,98.23,0.96
01:22.63,5952.0,10.0,98.23,0.96
01:23.33,6496.0,16.0,98.23,0.96
01:24.01,6508.0,18.0,98.23,0.98
01:24.70,4676.0,39.0,98.23,0.94
01:25.38,5056.0,9.0,98.23,0.96
01:26.08,5384.0,11.0,98.23,0.96
01:26.77,5688.0,15.0,98.23,0.96
01:27.80,6072.0,19.0,98.23,0.96
01:28.50,5460.0,21.0,1.18,0.72
01:29.19,3940.0,35.0,1.18,0.7

Thanks

 

[jim97gst]

Sorry for the double post. My connection timed out so I didn't think it took.