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JettaRedII
10-23-2006, 03:59 AM
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 (http://forums.vwvortex.com/zerothread?id=1484504&page=6) 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 (http://www.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.

mike-2ptzero
10-23-2006, 08:52 AM
People have been doing this for years on the B5's. I actually did the same thing back in 2001 but using a EBC to hold the boost at exactly 21psi.


Only bad part is that you have now removed a safety that is built into the dbw cars, so if for some reason one of the vac lines to the boost control blows or fails for some reason the car can boost all it wants and this can damage your motor. That is one of the reasons I used a EBC with over boost alarm which would then cut boost if it hit the max limit I set it for(25psi).

JettaRedII
10-23-2006, 09:12 AM
Very good point. So, if I put the boostvalve between the N75 and the wastegate actuator, and remove the diode, I could effectively accomplish the same thing. That way, I could raise the resistance of the pressure to the actuator by the boostvalve. Or, would the car then go into limp because the MAP is seeing 20-21 psi?

I’ll have to ponder this a bit.

marcini
10-23-2006, 10:58 AM
if the software is written for 18psi then you will most likely go into limp mode due to positive deviation code (simply overboost)

BranCKY3
10-23-2006, 11:23 AM
Originally posted by mike-2ptzero
People have been doing this for years on the B5's. I actually did the same thing back in 2001 but using a EBC to hold the boost at exactly 21psi.


Only bad part is that you have now removed a safety that is built into the dbw cars, so if for some reason one of the vac lines to the boost control blows or fails for some reason the car can boost all it wants and this can damage your motor. That is one of the reasons I used a EBC with over boost alarm which would then cut boost if it hit the max limit I set it for(25psi).

Yea my vac line from the compressor to the EBC got kinked a few times, it hit 29.1psi and the EBC really did nothing with the warning other than beep. I don't think it was able to do anything since it wasn't seeing any pressure so it couldn't open the wastegate.

k0mpresd
10-23-2006, 11:42 AM
yea..like mike said..this isnt new info @ all

good info none the less but its been around a while

on a sidenote..me and a buddy put a spec 2 in a car, accidently kinked the signal line to the controller and it just fed pressure to the wastegate constantly so it was running off spring pressure instead of not opening @ all

JettaRedII
10-23-2006, 12:07 PM
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.

http://www.msnusers.com/JettaRed/Documents/Boostvalve.jpg

matt719
10-23-2006, 01:30 PM
picture didn't work?

tunerb5
10-23-2006, 01:53 PM
you have 3 A4s?

JettaRedII
10-23-2006, 03:51 PM
Originally posted by tunerb5
you have 3 A4s?

More like a fleet. Two more and I get a fleet discount at the local dealer.[:D]

JettaRedII
10-23-2006, 05:34 PM
Originally posted by JettaRedII
More like a fleet. Two more and I get a fleet discount at the local dealer.[:D]

Oh, and they're all silver.[a4]

sean1.8t
10-23-2006, 06:19 PM
totally off subject, but why 3 A4s? why not just one stg 2+ S4 or something like that?

beejohn
10-24-2006, 12:10 AM
Originally posted by JettaRedII
Very good point. So, if I put the boostvalve between the N75 and the wastegate actuator, and remove the diode, I could effectively accomplish the same thing. That way, I could raise the resistance of the pressure to the actuator by the boostvalve. Or, would the car then go into limp because the MAP is seeing 20-21 psi?

I’ll have to ponder this a bit.

shouldn't hooking up the n75 and mbc in parallel make boost be max at whatever the n75 puts it at, and then the mbc only *limits boost below what the n75 is requesting?

is there anyway to hookup the n75 and mbc in parallel and increase boost at the same time?

JettaRedII
10-24-2006, 05:56 AM
The key is in fooling the ECU to think boost is less than what it really is. Otherwise, you go into limp. That's the purpose of the diode mod.

What I've noticed is that before, boost would drop down to about 12 psi at redline. Now it holds much higher an longer in the upper rpms. I've not tried to take it to redline in 4th or 5th yet, but certainly in 3rd it is holding boost much higher. That's when you really feel the difference.

mike-2ptzero
10-24-2006, 08:03 AM
Just a little info. The map sensor in the car is only used to read boost but the ecu doesn't use it to run more boost if the readings are lower, it is just there for a safety so that if readings are too low or too high the ecu will throw a code. So doing the diode mode wont cause the ecu to make the turbo boost more. Sounds like the reason your car only would hit 18psi is because the boost would hit over 21psi(which it did after doing the diode) causing the throttle to close a bit to control boost. Adding the MBC or EBC runs a set boost, so this is why the car is now holding more boost in the higher rpms and is basicly causing the turbo to hit max spool which is why the boost starts to drop. Only bad thing about that is now your IAT's are going to be much higher since the turbo is well out of its efficiency range.


BeeJohn - It sounds like he put the MBC/N75 in series since it is between the N75 and WG actuator. But doing it that way you can increase the amount of boost by leaking or blocking off the pressure being sent by the N75. Installing it in parallel with the N75 is only to control boost spikes and doesn't help with increasing or decreasing the amount of boost at all. This is because installing it this way gives you 2 paths for the pressure to reach the actuator.

JettaRedII
10-24-2006, 08:27 AM
Agreed and good info. However, the diode mod allows more boost by not indicating an overboost situation. The diode mod does nothing to the N75—it functions as usual. But the signal to the N75 to direct pressure to the wastegate never comes because the ECU thinks you’re boosting only to 17 psi, when you’re much higher. The diode mod prevents the ECU from limiting boost.

Our turbos are quite capable of hitting 25+ psi if the wastegate doesn’t open, they just won’t be efficient and will superheat the air. In my case, the Racetec FMIC does an excellent job at keeping the charge air cool. After a run, I can put my hand on the intake side of the IC and it will be quite warm, while the exhaust side is air temperature.