Weird MBC problem

[Sim]

I am running a dawesdevices MBC and i got a weird problem.

The MBC is losing boost as the RPM rises, and it is not because the turbo is small.

I set the boost controller to produce 18psi and the boost linearly tapers off as the RPM rises, lets say to around 10psi at the limiter. It is not because the turbo is small. Why?

I set the boost controller to produce 8 psi and the boost still tapers off linearly, lets say to 0 psi at the limiter. The turbo is surely capable of producing more boost than 0 psi at the limiter.

It is due to the MBC. Why can't it sustain the 8 psi through the whole RPM range?

Here's my log where you can see my 2nd gear WOT. I begin with higher boost than requested (thats good), then this almost linear tapering, and boost goes below requested at the end :(.

[ibizacupra]

Originally posted by Sim
I am running a dawesdevices MBC and i got a weird problem.

The MBC is losing boost as the RPM rises, and it is not because the turbo is small.

I set the boost controller to produce 18psi and the boost linearly tapers off as the RPM rises, lets say to around 10psi at the limiter. It is not because the turbo is small. Why?

I set the boost controller to produce 8 psi and the boost still tapers off linearly, lets say to 0 psi at the limiter. The turbo is surely capable of producing more boost than 0 psi at the limiter.

It is due to the MBC. Why can't it sustain the 8 psi through the whole RPM range?

Here's my log where you can see my 2nd gear WOT. I begin with higher boost than requested (thats good), then this almost linear tapering, and boost goes below requested at the end :(.

The dawes device is just a simple spring loaded thing is'n it...
increase the pressure to overcome the spring seal seat. what stops this just creaping with pressure rise?

How do you know the turbo can produce high boost at high rpms?

Bill

[salamanzer]

i agree with bill -

By the looks of things your turbo cannot produce the requested boost pressure at high revs.

The problem can be that the turbo is overspinning and the wastegate is dragging it back down.

My car has 1.5bar peak, 1.4bar hold and 1.1bar at the limiter.

Turbos cannot produce the peak pressure all the way through the rev range because they will overspin and destroy themselves!

Plus in second you will not get max/peak boost from your turbo due to the reduced engine load - try reproducing the graph in 4th or 5th!

J

[Sim]

Guys,

i know i should have been making a log with the MBC (dawesdevice) set to 8 psi (and not with ~16 psi). As i wrote in my first post, it does 8psi only at the beginning, then it will taper to 0 (ZERO) psi at the limiter. I think you did not mean it seriously that the K03 can not boost more than 0 psi at the limiter. Using the N75, requested and actual do match!

MBC is NOT holding the 8 psi at the whole range, forget about 16 psi. I want only 8 psi but at every RPM. it cannot do it. why?

[Sim]

I've modified the log. This is a hypothetical boost log, this is how the MBC works on different boost levels. It does not sustain the boost perfectly. Probably not that dramatical as the diagrams shows, but hopefully you get the idea. It has nothing to do with the turbo being small.