I posted a few days ago about slow boost coming on with my 2.7t A6 after VAST tuning.

I knew the VAST tuning had nothing to do with the problem but something wasn't right. When I first picked up the car is was extremely responsive. I had boost very low and the car felt great.

After a while that tapered off and the boost was not coming on full until about 3300rpm.

They put a new N75 on it which turned out to be defective and swapped it out today for me. That solved some of my boost issues. Its not as late but then again its not how it was.

Their explanation which makes sense to me is that the N75 was bad from the get go and it was probably cracking the wastegates leading to boost down low.

A MBC should mimic that run in parallel with the N75 and let the boost hit harder than with just the N75 running things.

I had to get a boost gauge first and they offered a reasonable MBC.

I'd really like the option of adjusting it in the car though...and I'd like the option to run off the N75 or the MBC. Reason is the MBC will be more harsh versus the smoothness of stock.

If we're going out or want to take a nice cruise I'd like to be able to keep things smoother.

Their MBC doesn't have remote control. I've seen these $7.99 controllers on Ebay that are remote. They are not complicated pieces so the price doesn't scare me away, cost me $3.00 to build my own MBC years ago.

I really want the remote control so I can dial it down in the car.

Anyone use one of the Ebay ones? I suppose I can take their MBC and extend the hoses out. Good thing about extending the hoses out is I can pipe the boost gauge in right there.

Thanks

 

Never heard this. How do you figure? MBC in parallel doesn't raise boost or bring it on any sooner - N75 will still control all boost below the MBC setting, and the parallel setup will only serve to bleed off excess.

You'll actually be seeing less boost, with spikes capped.

Moreover, if your N75 was cracking wastegates earlier, you'd be seeing LESS boost, not more.

Also, when running in parallel, you're not going to get any driveability issues with on/off throttle like you would with MBC only. If you want to switch between a parallel and MBC only setup, you can always just throw a valve in and turn it on or off.



No experience with inside-cabin adjustments...

 

I used incorrect wording....I had it clear in my head and translated it down onto paper wrong.

The N75 seems to be set for smoother spooling. Making the car more refined.

An MBC stays shut until desired boost level, the N75 might "flutter" the gates to get smooth spool. So the MBC should spool the turbo faster.

You are correct though not in parallel...they'd need to be separate.

Although if I put the MBC before the N75 wouldn't that work? If the N75 is not seeing boost at all until the MBC lets the pressure through....

My goal is to get faster spool, down where I had it before.

Whatever was wrong or right, before the new N75 I had boost very low, just looking to get that back.

 

The N75 is a solonoid. It is controlled by the ECU.

 

You have a problem with your car. If it ran well before and doesn't now something is broken. Your "solution" is not a solution. It's a band-aid at best.

Are you prepared to run an MBC? Got a wideband gauge and some sort of way to adjust fueling to tune for the MBC? You can't just override the ECU and expect that it will compensate and all will be roses.

Ebay? $8 for a MBC? It just screams "quality".

 

and an MBC won't fix it, maybe only mask it. I run MBC only, but I have the tools and patience to do so. Also, why have VAST tuning if you are going to HB it. Did you pressure test it? That is where I would start.

 

I'm not band aiding anything.

The car runs fine. It has the tune in it for 15lbs. I am not running more than 15lbs.

What I am attempting to do is get the turbo to spool faster.

I don't plan on running more than 15lbs, the reason for the MBC is to get the turbo to spool faster and get it to hit harder down low.

According to VAST and I agree with what they say, the speed at which it spools is normal. The car feels fine, it just doesn't have the same punch as when the valve was bad and holding the wastegates shut longer.

$8.00 boost controllers are not the end of the world you know. I ran a 700hp turbo car off of a $3.00 ball style boost controller that I put together.

The problem with the MBC is its not too smooth, its going to hit low and hit hard. Thats fine for when I want it that way but I'd like to move it back over to the N75 for normal driving.

 

Yes the car was pressure tested, everything was gone over, I've logged the hell out of it.

The problem was the N75 all along.

 

The concept remains the same...the control of the N75 seems to be set to create a smoother spool up.

 

that is your problem. 3. If not in Parallel it is MBC only or N75 only. 4. MBC before N75=pointless 5. If the problem occurred immediately after N75 was installed check the install, are the hoses cracked, reversed, etc.......................