you need the right mixture of everything really, when my cab was mapped (admittedly it was a 1900 cvh not a 1600 so would be less laggy anyway) it had a stage 3 ported polished big valve head, port matched inlet, cvh34 cam, and a t3 with a .48 housing, 360 bearing, but the rest of the turbo spec was unknown,it only did 210bhp with 250lb/ft, it was on full boost before 3000rpm, peak torque was at 3500rpm, but after 5000rpm it wouldnt make anymore power what so ever, jamie said the turbo was restricting it and holding it back, and as said above that was with a .48 t3 and a good spec head and cam which had done 246bhp on a previous car so we knew the head wasnt the problem, but the compressor side of the turbo was completley unknown which we think is what was holding it back.