I logged requested (spec) boost VS actual boost today.. Its in Word doc. so check em out and tell me what you think... I accidently deleted the log going past 6k rpms, but it seems to me that overallmy actual boost is lower than requested. This is using the stock N75 valve. I think you can see towards the bottom of page 6 I go into limp mode (get the 17964 - Charge Pressure Control: Negative Deviation fault code.)
I dont have logs from it, but I never had this problem when I was using the N75H (race) valve. I had posted when I orginally swapped them that there were no problems, but there deffinately are. Ive got a mbc on the way so I can try to bypass the N75 altogether and see what happens. I have checked for leaks everywhere but the wastegate actuator hose but havent ran a boost leak test. Just looking for some feedback... On anything.
http://putstuff.putfile.com/89887/1588935

If you notice strange jumps in rpm's/boost its because I was pausing and resuming the logging.

ALSO, I see numbers as high as 2380 mbar... According to a psi/mbar calculator, that equals 34psi.....? wtf?

 

I just quickly threw together a little graph and plotted the Specified and Actual Boost values:



The two curves seem to follow each other pretty good but I can see what you mean that actual seems lower than specified especially at the peaks. Maybe a boost leak test would explain the situation (I'm no expert, this is just a suggestion).

 

Wow thanks! Did you just imort all that into an excell graph?

 

I just copied the 2 last rows from your Word doc, pasted it into Quattro Pro (similar to Excel) and did a "quickgraph". There might be other ways to do it but I am not exactly a computer expert, sorry...

 

Don't forget, this is absolute pressure (it includes atmospheric pressure). You have to remove the atmospheric pressure (approx. 14.7 psi). So the turbo's boost pressure would be 34 psi - 14.7 psi = 19.3 psi.

 

Thanks man.. Im going to go get the parts to put this together: http://www.a4mods.com/index.php?page...boostleak.html

 

you're not off by much as far as boost goes. from what I can tell your peak is about 50 mbars off of the supposed peak. the RPM range is a bit different, but all in all I'd say you're pretty close to where you need to be. you could definitely be losing 50 mbars at a leak somewhere. but again. thats not a huge difference in the big scheme of things.

check that. your "actual" is 50 mbars higher...at lower RPMs. unless I'm looking at this completely wrong.....
I've got a graph if you wanna see it of boost plotted against RPM's. you are falling off at the high end of the RPM range, but that's probably a case of an undersized turbo, not a boost leak.

 

Here is a link to one I designed, it works very well but involves a little bit more hardware to build (the main link is included in the upgrade link).
http://www.audigeeks.com/forums/index.php?topic=2139.0

 

You are right, I THINK (not 100% sure) that the reason is that the sensor is reading atmospheric pressure only (no turbo boost) which is about 1014 mbar (which happens to be above specified but the pressure can't be less than atmospheric pressure... right?).

 

How did he get that chart in there?!

HA

I can't figure it out!