Boost falling at 4500rpms. TIP?

[smarrick]

So my friends car has apr1+ and it boosts right up normal peak 19psi holds 18psi. Then no matter what gear around 4500rpm the boost just starts falling down. It gets to about 10psi by redline in 3rd.
Tip collapsing?
Anyone know what this is.

The Car.
2004 A4 18.t AMB 6spd Quattro
Apr 1+. Some unknown brand exhaust after downpipe. Billet DV with heavyist spring Factory everything else.

[mister_tu]

Possibly the shitty stock plastic diverter valve is leaking and is not holding boost.

It could be a number of things, honestly.

[audipotential]

Possibly the shitty stock plastic diverter valve is leaking and is not holding boost.

It could be a number of things, honestly.

Most likely this is the answer

[smarrick]

ok forgot one. has aftermarket DV with heavyist spring

[A4natomical]

thats a stock turbo for ya.

[smarrick]

I was wondering that. But my friend has a gti with 1.8t and apr chip and it cranks out 18 all the way through.

I don't think it is just the little turbo.

[AudiA4_20T]

thats a stock turbo for ya.

... GTI turbos are a bit different than ours and also the engine isn't working as hard to get the car moving with the FWD... that may not matter but its a guess

[A4natomical]

didnt know it was a gti. my badd. alright ill shut up.

[smarrick]

No the problem is with the a4. I was comparing to a gti.

[gtimart]

I think the 180hp GTIs have the K03s just like us. The TIP collapsing gives some surge, but I wouldn't think it would cause an "underboost" condition all the way to the end.
Also, the peak psi should probably be higher than 19 for a 1+ right? Closer to 21 ?

[smarrick]

Yes as far as I know same turbo same motor. I know the a4 is heavier but I'm not talking about a loss of power at the end I'm talking about a loss of 10 psi. Something is up.

Anyone running apr1+?

gtimart you are right FXko3 is same thing. What boost are you running? Does it ever let off?

[gtimart]

I don't remember my only log I did a few months ago. Boost certainly falls after 4500-5000rpms, that small K03s cannot hold 18psi all the way. I think it will peak around 19.x psi (24xx mbar IIRC)? I think my comment about 21psi was wrong in my earlier post.
I guess it goes down to around 13-14 psi at redline normally.

[05A$SE]

i have apr stage 1 with forge 007 (yellow spring) and i peak at about 19psi and then it falls to about 14 psi around 5000rpm. i believe all k03's drop pressure after 4500rpm. its just the way the car is. on stock file the car runs about 7 psi after full spool and when its in high rpm it wont reach full boost. this is in my personal experience and a little bit of what ive heard. i dont know if i'm fully correct so i'm open to any response to this post.

[A4ringedONE8T]

No way any K03, VW or Audi, is holding more than 14-15psi past 4500. 12-13psi 5k till redline is 100% normal