I have a Joe P XZ MBC and I am getting boost spikes. When set to 20psi it will reach and hold 20psi fine if I roll on the throttle smoothly, but if I am at 4000rpm in 3rd and I nail then throttle it spikes to 22-23psi and comes back to 20psi, especially on cold nights!

Without debating whether or not the spike is bad for the car, can anyone suggest how to get rid of the spike? I was thinking about making the tiny breather/vent hole in the MBC housing a bit bigger. Do you think this would help? My MBC hose routing is already short.

Is anyone out there using an MBC with zero spike of do I have to go EBC to get this performance?

 

i think whats happening is the turbo is building more boost than can be evacuated by the wastegate. Thats why you have a big spike in the higher gears with the engine loaded, at low rpms. I have the same thing. I get a ~3 psi spike in a low gear around 3k rpms and it slowly drops ~3 psi when i get to redline. Ive been wondering about this myself for some time. I think the only thing to do is port the wastegate, or buy the 10.5 cm^2 housing because it has a revised wastegate flapper. Im not sure if it evacuates the exhaust gases any faster though.

 

Funny thing...my JoeP spiked when I first installed it, and the peak boost varied from gear to gear. Then after getting dynoflashed, the boost holds rock solid from gear to gear.

I would think that the spike is mechanical, and has nothing to do with the tune, so maybe it was a coincidence. If so, then the problem went away by itself.

Also, you're going to make more boost in cold weather, so you have to adjust the MBC to bring it back down to 20 psi (then readjust when it gets warm again).

 

If you want to get rid of the boost spike, don't floor it at 4K. The stock turbo spools relatively fast and that's what happens when you have 4K RPMs worth of air coming past it and then floor it. It's not the MBC or the tune.