Lazy boost curve?

Hey guys, Was tuning a friends car tonight.. Isuzu G200z 2.0L with a T28 Turbo in a Gemini. I fitted the Haltech sprint 500, Running and tuned no probs... Just the boost curve was a little lacking from what I expected...

Tuned to spring pressure first (10psi) and it didnt reach 10psi until 4500rpm and boost flat lined from there until peak power of just over 6000rpm.

Using the haltech and boost solinoid and adjusting duty cycle I raised boost in stages up to 15 psi... I expected it to keep the same curve up to 10psi but to shoot upto 15psi quick quickly from 4500rpm and flatline from there... But it was a very linear if somewhat concave curve not making 15-16psi until redline.

So yeh, just wondering what are the things that will effect boost response? It does have a pretty rough looking 2.5" exhaust on it which Is likely a restriction, How much bearing on lag does exhaust back pressure have?

Not sure what A/R the turbo was... I know this is a major factor.

No apparent boost leaks.

Pretty much just wondering... as a Tuner besides getting the AFR and timing correct what else can you do?

i'm not able to tell if you were running an internal or external wastegate.

in any case, if you were just tuning on spring pressure, then there was nothing to support the spring to help keeping the wastegate flap closed so that your turbo could build boost more efficient.

basically the exhaust gases pushed the wastegate a little open.

as soon as you turned up the duty cycle of your solenoid, it was helping keeping the wastegate closed until the target boost was reached and then started opening.

very simple, but should get you in the right direction ;)

It depends on the setting that your using in the ECU, the duty cycle isn't the only factor that can affect boost delivery.

I'm working on the Link software just now so will use this for reference:

you have Open loop or closed loop, RPM activation, MAP activation.

It sounds like your using open loop as your mentioning only adjusting duty.

Do you have an RPM dependent duty cycle available? what you could do is ramp up the duty cycle lower down the rev range and taper it off so that it holds boost.

Do you have any boost trim's in action?

have you raised your boost limit? silly question but have seen it happen before