Manual Boost Controller in Parallel with N75 to Correct Boost Spike

[clockwise33]

Hello again guys,

I wanted to share some good results of a recent project on my MKV. I've got my APR K04 dialed in really nicely lately with more time for logging. It pulls hard and smooth to red line, peaks 260ish g/s MAF, about 315whp on Virtual Dyno. One slight issue has been occasional overboosting past the sensor max (about 26psi on the gauge), especially when shifting and getting back on the throttle. This never throws a code, however you can see the ECU correcting by closing the throttle and pulling timing for protection, making the car actually feel slower. I decided to try plumbing in a simple ball/spring MBC in parallel to the N75, exactly how it is described in this link: http://www.boostvalve.com/vw-1.8t-overboost-fix.html. In my opinion, this is needed for a K04 to run right on a car with the 2.55bar boost sensor because the requested boost is so close to the sensor max. This is why most K04 tunes for TSI and some for FSI require the 3bar sensor, however my car is a 2006 and the ECU is not compatible with a 3bar sensor.

It was a big pain to install with very little space to work, however it worked flawlessly. Basically, you are setting the absolute max that the boost can reach, while allowing the ECU to maintain control. The below graphs show how the MBC fixed the spiking on a WOT 3-4 shift on back to back days on the same road and conditions.

Boost spiking above sensor max causing throttle closure and timing pull:

Boost spike above sensor max eliminated by MBC, keeping ECU happy:

 

[ROH ECHT]

1) I would make sure the intake valves are cleaned...then see if it still spikes. I've recently seen one with an over-boost code. Owner ran around trying to find the cause. Ended up taking it to a VW shop. They determined the inlets were clogged and causing it. Once cleaned it ran perfect.

2) You could also reduce the WGA preload and find this will eliminate the spike, yet still hold its boost target to redline.

 

[clockwise33]

1) I would make sure the intake valves are cleaned...then see if it still spikes. I've recently seen one with an over-boost code. Owner ran around trying to find the cause. Ended up taking it to a VW shop. They determined the inlets were clogged and causing it. Once cleaned it ran perfect.

2) You could also reduce the WGA preload and find this will eliminate the spike, yet still hold its boost target to redline.

Both good points.

I cleaned my valves when I installed MK6R rods/pistons about 9,000 miles ago so they should be good.

I've adjusted my wastegate probably a dozen times since fitting the K04 in 2016. The problem for me is the amount of preload that must be removed in order to calm down the spike results in late boost onset and lower top end air flow (245g/s vs 260+). With the parallel MBC, I get to eliminate the spike while keeping the low end response and top end power.

 

[ROH ECHT]

OK...since you've already addressed those possibilities, yeah do a MBC.
I think I have a pic GIAC sent me for boost spike limiting...and to make the install easy to understand...yep, here it is; ("Ambient Pressure" is the turbo inlet line to N75__"From Turbo Housing" is obviously the compressor line to N75)

 

[clockwise33]

OK...since you've already addressed those possibilities, yeah do a MBC.
I think I have a pic GIAC sent me for boost spike limiting...and to make the install easy to understand...yep, here it is; ("Ambient Pressure" is the turbo inlet line to N75__"From Turbo Housing" is obviously the compressor line to N75)

View attachment 197968

That's exactly how I installed it. I also placed it as close to the wastegate as possible to improve response, while allowing access for adjustment.

 

[ROH ECHT]

Excellent. Mine was built in May or June '06 but is an '07, and I ran a 3 bar MAP when I ran the Driver Motorsport K04+ tune. Data would only register 2.58 bar even with the 3 bar sensor and DM tuned to 26 to 28 psi. This is why I had to get the boost gauge. Originally, when the gauge was installed shortly after loading the DM file, I saw it was boosting over 30 psi. He adjusted it and I had to mess with preload due to surge above 28 psi.

A United Motorsport custom tune for a 3 bar sensor, tuned by a UM dealer on the dyno, would likely work...shelf files, no.

This was DM K04+ open-loop boost data;

This was the DM K04+...60 mph to 120 mph acceleration. Less than 8 seconds;