My mates evo 8 has recently started having problems when it comes to his turbo.

The car is now making less boost than normal. The turbo still spools like usual but the boost kicks in is delayed a couple of thousand rpm.
The only mods are
- Full exhaust from the dump pipe
- K&N typhoon intake
- Turbosmart bov

I was thinking it might have something to do with the ecu because it hasn't be retuned sinced the mods have been installed.

Does anyone know what the problem could be?