Just checked my RR graph, and why does my PSI Drop?
 

Car is an MY03 JDM STi

Just having a scan through my Rolling road print out from scoobyclinic,

at 2800rpm it goes from 6psi to 21psi at 4000rpm, then thats it, drops down straight after that going to 19 at 5k revs, all the way down to 16 at around 6.4k, is that normal?

Why cant I have 21 psi all the time :D?

You could with an after market boost controller, boost generally tales off at high revs and its not wise to keep high boost in the upper rev range for too long.

It is noraml and has probably been mapped that way to protect your engine

Sounds perfectly normal, the boost will peak and then tail off near the end of the rev range. Nice and safe :)


Also an AVC-R will help you control the boost through the rev range.

You can if you have a big enough wallet....;)

The main reason for this is that as the volume of air required by the engine increases the turbo starts to run out of puff so pressure drops. To get an idea try blowing hard down a narrow piece of plastic pipe then try down a piece of hose pipe. You will find it more comfortable to blow down the hosepipe as the pressure is less.