^%$#&in Boost spike!! Help pls

[John Hartman]

So, I have spike.  Have had it for a bit, but I figured I could whip it.

No such luck.

I have a BBC(Busta Boost controller), all my vacuum hoses are new.  Good connections.  I have the boost source for the controller coming from the compressor outlet elbow.  Stock nipple.  I even drilled it out slightly to make sure I had adequate flow.  The boost source line is at most 6" long, and the wastegate actuator line is less than a foot for sure.

It will spike to 20 or 21 PSI and then fall off to whatever I have it set at.  Currently 17 psi for testing purposes.  If I set it to 19, where I'd like it, the damn thing spikes to 23 or 24 psi!!!

In no way is this a knock on Vlad's controller.  I just wanna clear this up, its hard to tune like this!!

[Jack Lee]

Man that sucks. Does it spike if you source it from the BOV? In theory this would be worst (longer line) but you never know. Mine's connected to the BOV and no spike. Of course, I didn't have a spike when it was connected to the outlet elbow either though.

[John Hartman]

yea thats why I changed it back to the outlet nipple.  I even had the nipple welded on, and bought new hose to make the BOV line one piece.

[Travis Merrick]

do u have a ported o2 housing?  You should do that and get a 34mm flapper put on, while ur at it, port it out =)  I dont think its anything that can be controlled by vaccum lines man, you have a 3" turbo back.

[Kimyee Lai]

Ported O2 and bigger wastegates are more remedies for boost creep.  Boost spike is very likely BC issues.  Does it spike if you bypass the BC and go directly from the boost source to the actuator?  I have my old MBC you're welcome to try...

[Vlad Busta]

Hey there John, the b-bc is very sensitive to adjustment.  Once in the range of the boost that you want just turn the adjustment screw while keeping the lock nut tight.  You know this already since you've modified the b-bc  :wink: .

I have another one sitting around so you can give it a try if you want.  We can probably meet up this weekend if the weather is good.

Have you checked for any boost leaks.  These can cause some funky things to happen.

Later, Vlad.

[Jeremy Clarke]

You say this happens at 17 and worse at 19, but does it happen if you lower it to 15? In either case you may want to test your WG actuator before getting more serious, (ie. porting things) the Haynes outlines the proceedure, just borrow a pump from Crappy Tire. It may be that your actuator has a leak. Also, I know Vlad puts a tiny bleed hole in his MBC's you might try blocking that off with a screw and go for a run. I have never used the bleed hole in my MBC's and have never heard of a problem, then again I instruct it to be run off both sources, and that may have somthing to do with it.

[Travis Merrick]

Spike, not creep Travis, dammit! yah I know I overlooked what I was reading.  What kinda psi can the springs in the BBC handle.  Im sure there is a grade rating or psi rating on springs, and itmaybe have broke or something.  Could it be a possibility that the spring may be compressing to much upon initial boost hitting the ball bearing making it going up to much than coming back down? just an analogy u may wanna look at.

[Kimyee Lai]

You need the bleed hole there to vent pressure after the boost source decreases...This is the scenario if the ball is sealing the MBC perfectly.  Boost comes up, pushes against the ball, which pushes against the spring.  At a certain pressure, the spring force is overcome and the ball comes off the seat.  Air travels through, goes into the wastegate actuator and opens the wastegate.  Now, if the boost now falls off and the ball reseats itself, the entire assembly downstream of the ball stays pressurized.  This means that the wastegate will be kept open and your spool time will be longer.  The vent hole is there to prevent this from happening.  

You might want to try different sized vent holes...Theoretically, a larger vent hole would probably cause more of a spike, because it'll take a larger opening in the MBC to pressurize the post ball portion of the MBC enough.  I'm not sure what size vents Vlad has, but a 0.5mm vent hole worked fine for me.  I had a system in place where I could screw on different sized vent holes, curtesy of the head of a mechanical pencil...so I could go 0.5, 0.7, 0.9mm .

[Jeremy Clarke]

You need the bleed hole there to vent pressure after the boost source decreases...

Yeah, I know the theory behind the vent hole very well, but I have never had one and never had a problem nor have any of the dozens of people I sold them to. My bearings are high grade SS, special ordered and cost me a lot so I'm sure they seal. I really don't know why or care why it works, I'm just saying that blocking it and running off both sources is worth a try.

[Kimyee Lai]

My bearings are high grade SS, special ordered and cost me a lot so I'm sure they seal. I really don't know why or care why it works, I'm just saying that blocking it and running off both sources is worth a try.

The seal also depends on the seat, not just the bearings .  Besides, the adjustment screw is also a likely vent source.

[John Hartman]

ok, Travis, you answered your post for me

Kimyee, I totally forgot to try running just a hose from the source to the actuator.  I will give it a try, thanx.

Vlad, this one is not modified, except that I glued in the top piece so that it would not turn if I turn the lock nut.  I never even took it apart, just some real thin CA (crazy, but better brand) glue and let it flow into the threads.

Drivin me nuts  Pulls like a bastard at 22 psi tho, hehe, but way too much knock.

Oh, and Vlad, how the hell do you turn it when the nut is tight??

Anyone local wanna lend me thiers for a short time??  Like to get this narrowed down to either the controller, the j-pipe or a leak soon.