MBC quirks...need help!

[Aleks]

Alright, I started using MBC on my car, nd it worked great for the first couple runs, I wouldn't spike anymore, hold 18-19psi consistently, but then suddenly started overboosting in partial throttle situations....I would hold 1/4 throttle, and the boost would build all the way past 15psi.....after that started happening, I would spool until 14psi, and hit soft limp, even after a few shut down/start up cycles, I couldn't get past this limp.....I have the MBC run in between my N75 and my wastegate actuater......

Otherwise, if my car would run like it did the first bit, I would be very impressed, it was smooth, no more surging/hesistation at WOT, plus a few more PSI .....any ideas??

[Kor]

Re: MBC quirks...need help!

I thought you were de-modding this year?

[Aleks]

Re: MBC quirks...need help!

nope.....what gave you that idea??

[Kor]

Re: MBC quirks...need help!

Must have been confused.

[Aleks]

Re: MBC quirks...need help!

any help?

[Flanders]

Re: MBC quirks...need help!

That's why I'm not running an MBC...WOT was great, but part-throttle (oddly enough, which is what I do most of the time anyway) was absolutely brutal.

[Aleks]

Re: MBC quirks...need help!

I've got it kinda working with the right throttle modulation, I can still drive great...I don't want to lose that smoothness now......I wonder if that overboost kit would fix this?

[NeonGTI]

Re: MBC quirks...need help!

I've got it kinda working with the right throttle modulation, I can still drive great...I don't want to lose that smoothness now......I wonder if that overboost kit would fix this?

Nope. Got it.

[Klobi-One-Kinobi]

Re: MBC quirks...need help!

Try an ebc? Kinda pricey though.

[Aleks]

Re: MBC quirks...need help!

Are there any EBC's that can let me boost over 14.4? I'll try a different boostvalve shortly....

[NeonGTI]

Re: MBC quirks...need help!

Are there any EBC's that can let me boost over 14.4? I'll try a different boostvalve shortly....

I had a 'boostvalve.com' valve on as well as an el cheapo from my turbo daytona and they both did the same thing at half throttle - they made rippin boost.

I also had the overboost kit for the boostvalve. I think they are sitting in a tool box somewhere in my house. I keep going back to the stock n75 for the predictability, linear progression of power and ability to control boost levels.

[Kor]

Re: MBC quirks...need help!

Its an on/off valve so it can only be on or off. The N75 is not an on/off valve, it can be in any position to allow a tiny bit of flow or a lot of flow. That is the simplest explanation.

As long as you put an on/off valve in the system, you will be able to feel when it goes from on to off, and it will trigger limp mode if it does so under low requested boost (part throttle).

A programmable solenoid type valve is a better idea. I would recommend something simple like the Greddy Type S.

[Aleks]

Re: MBC quirks...need help!

So, a different N75 wouldn't change things, I'm still running the F valve, and its still connected.....I would think that a J or H would be a little more lenient with spikes, as it delays the signal slightly.....no?

[Flanders]

Re: MBC quirks...need help!

I found them both (J and H) to give me erratic part throttle behavior :( I went back to my stock "C" valve.

[Kor]

Re: MBC quirks...need help!

So, a different N75 wouldn't change things, I'm still running the F valve, and its still connected.....I would think that a J or H would be a little more lenient with spikes, as it delays the signal slightly.....no?

The problem isn't the N75 valve, or spiking... you can take it out even or leave it in and you will see the same basic behaviour pattern. There is no delaying the signal with an MBC in-line - the MBC is either open (0% delayed) or closed (100% delayed).

Putting the MBC in a sort of "overboost" configuration in parallel to the N75 will remove this problem, but also will negate being able to control (increase) the boost. In parallel the MBC will just let you limit the max pressure (spike).

You could try using a valve that is not on/off. For example a pressure regulator/restrictor or bleed. However you will only be able to make minor changes of maybe 1-2 psi before the part throttle problems re-occur due to the changed boost curve.