This may be of interest to some. I am running the GIAC Hammer file for the K04. It’s been great, but the sustained max boost has been 18 psi. I wanted a little more, like 20 or 21 psi, but could not adjust the boost with the software like Revo does. So, here’s what I did.

First, I made the diode modification to limit reported boost to whatever 4.7v represents (17 psi). That took care of limiting the boost to 18 psi. However, the problem now is that boost would peak to 25 psi and hold around 23 psi—more than I wanted.

So, how to limit boost? A boost control valve from Boostvalve.com. But, instead of hooking it up according to instructions, I fed the boost input side with a line from the intake manifold. (Boostvalve operates by bypassing the N75. The problem was that the diode mod effectively defeated the boostvalve by keeping the N75 open and never sending pressure to the wastegate actuator.)

Now, the car is boosting and holding at 21 psi, but still retains the nice drivability that the N75 provides.

 

Awesome.. But what did you do to make adjustments to your fuel/timing to make use of that added boost?

 

Nothing. That's why I'm keeping it to only 20 psi. My fuel trims indicate that I'm running a bit rich as it is, so I will drive cautiously until the trims have adjusted. The additional 2 psi shouldn't be a problem. Now, if I was running 24 or 25 psi, then there'd be a potential problem. But I'm not overly concerned with 20 psi.

 

So you feel a difference in performance then or what?

 

It does feel stronger. I’m not a big fan of dyno’s just to prove a point because I’d rather spend my money on real stuff to make my car faster, etc., but I feel that it’s pulling stronger and longer. Even with the K04, you could feel the power drop off at higher rpms. Now it feels just a little stronger in the upper rpm range.

 

about what rpm's did the k04 drop off at before? The k03 drops off around 4500-5k rpms and i thought the k04 pulled longer than that?

 

I'll check again, but that's about right. Now, boost holds almost to redline.

Here’s a pic of my setup. As long as the line from the manifold to the boostvalve is intact, I can adjust the max boost pressure. Up to 18 psi the N75 will work as normal. At 20 psi, the boostvalve opens to the wastegate controller and boost is held constant. Boost still peaks above 20 psi, but not very high and quickly settles at 20.

 

Cool. Speaking of all this... Im about to get a mbc because i overboost near redline in 3rd+gear and go into limp mode. I get that damned "negative deviation" fault code that no one has the solution to. Im hoping a boost controller will help, but i really dont want to turn the boost down. It holds between 18 and 20psi. I might try 15 or so with the mbc.

 

jetta did you try to run just a mbc with out a n75 or the diode mod?

 

I have in the past and felt that boost was too erratic. This is kinda the best of both.