Boost drop at 7k RPMS.

[aspec04t]

Setup: 2005 RSX -S CN KIT, 750CC Injectors, 3in exhaust, No cat, Motec 3Bar , and K pro turbo T3/T61. (Garret version of SC61) and boost control done by the built in boost control feature in the k pro.

Problem : Trying to maintain boost at 12 PSI.
Car builds 12.5PSI @ 5700RPMS then once I hit 7500RPMS boost starts to drop to 11.2 PSI and by the time I get to 8300RPMS I am at 10.1 PSI. I was suspecting the issue was with the cam angles. So I decided to Lock the cam at 30 degrees at 7500RPMS see if held boost and it did not work, lowered cam angles to 25deg and on to 20 and it didnt seem to have any effect . Here is a datalog of the car . The pull was done in 3rd gear any help or advice on what can be the issue would be appreciated. Thank you in advance .

[Spunkster]

This sounds very normal for turbos. I have a SC61 on my car and it had a wastegate spring for 8 psi, and it would go to 8 psi and then taper of to about 7psi at high rpm.

It may also have to do with where you have tapped your wastegate source of boost.

[aspec04t]

the wastegate vaccum source is the compressor housing of the turbo. Thanks for the reply.

[Hondata]

What you are seeing is the pressure drop across the intercooler at high flow. Move the wastegate pressure source to near the intake manifold.

[aspec04t]

Ok, so I had suspected that the issue might have come from the boost controller solenoid. I disconected the boost controller and ran a direct vaccum line from the compressor housing of the turbo to the bottom port of the wastegate. The pressure drop was still present . However since I have the .6 bar = 8.7 psi now the pressure drops to about 6.6 psi. I then went a sep further and thinking maybe the 3 bar map sensor was the issue. I disconnected the 3 bar and since i tapped the wire i still had the old map clip there so I connected it to the stock map sensor. Still 2 psi drop from 7k to 8.6k.

Further Information: I used to have a turbonetics 60-1 with a stage 5 exhaust housing. Then the seals went bad on the turbo and I decided to swap it out for a T3/T61 Which is the garret version of the SC61. With the 60-1 I never experienced this issue. Its only since this happend that this issue has come up. The manifod is the same , intercooler, pipes , wastegate as when I had the 60-1.

Thanks doug for the respoce. So your saying cap off the compressor vaccum line and run a line between the turbo and somewhere in the intake mani?Why wouldnt this have happend before ? Just curious.

[aspec04t]

is it possible that the manifold be cracked, i think its unlikely since it spooled the other turbo just fine. ..