Running a manual boost controller in parallel to the N75 to control boost spikes

[EvolutionArmory]

Generally speaking you want your N75 and tune to have complete control of your boost but the reality of that isn’t always possible. People have different tunes, different mods, live in different altitudes and many off the shelf tunes don’t offer the ability to tweak tunes to perfect aspects of the tune or charge a good amount of money to do so.

My issue was with wastegate crack pressure. If I set it too low, peak boost came on too slow and I wouldn’t hold boost up top. If I set it too high, the boost would spike and the ECU would pull timing. So what I decided to do was a trick many 1.8T and 2.7T big turbo folks have been doing for years.

I set my wastegate crack pressure high enough to make good boost up top and use a manual boost controller to limit peak boost to whatever I set it to.

The rule of thumb for wastegate pressure has always been to set crack pressure to about half of your total boost so I set mine to 9. I was able to hold 20 PSI on my K04 to redline but the boost spike was bad because my N75 couldn’t work enough to deal with it.

The principal is simple. Plumb in a boost controller so it runs along side the N75.
Attachment 198592

Here’s a log of my boost without it. Our MAP sensor will only read 22.5 PSI so I added what the 30 PSI spike would look like.
Attachment 198593

With the MBC plumbed in parallel, I can set my peak boost to whatever I want. It’s basically adding a 2nd vent for the wastegate and you still get full factory control. Here’s a log with only a 22 PSI spike after installing it. I can lower it even more.
Attachment 198594

With the boost spike, the car was pulling way too much timing down low and even when boost fell in line, the timing was all over the place. It’s like the ECU couldn’t recover from it. I was making power with boost but losing power from timing pull.

Being able to control my peak boost not only fixed my boost spikes but also cleaned up my timing logs tremendously.

Just thought I’d share.



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[AudiB720TS]

Which MBC was used?

[EvolutionArmory]

Integrated Engineering. I think it’s the best MBC out there for this car.


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[EvolutionArmory]

Image1657063697.274325.jpg

I mounted it right to the rad support for easy access.


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[AudiB720TS]

Integrated Engineering. I think it’s the best MBC out there for this car.


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Was looking at that, but seems out of stock everywhere and link on their website is down. Wonder if it is discontinued.

Looking at TurboSmart and Grimspeed also, but I like that IE has a bracket and fittings looks to be in the right size.

[AudiB720TS]

Ordered a GFB ‘Atomic’. Good reviews, discreet design that should be easy to hide.

[AudiB720TS]

EA, can you clarify need for vacuum "T" connectors to run MBC inline? Tee's are needed and are they 3 mm or 4 mm ID?

Thanks

[EvolutionArmory]

Measure the barbs on your N75 and MBC. That’s the size inner diameter hose and T couplers that you need.


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[AudiB720TS]

Measure the barbs on your N75 and MBC. That’s the size inner diameter hose and T couplers that you need.


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Well obviously. I wanted to avoid breaking the hose clamps before I had all parts.


Anyways, does this look correct to you? Your attachment's (first post) are broken. This is an attempt to re-work that other diagram you shared floating around the internetz, in order to visualize it better.

[EvolutionArmory]

Should work fine like that.


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