Boost drop off with HKS dump..?

[SLY33]

Having fitted the new HKS split dump to the GT2530, boost drops off at the top end quite badly. It drops from 17.5psi down to about 14psi, killing the top end power figure. Anyone know why!?

Simon from Morpowa has tried everything, and thinks it could be a wastegate actuator problem (a standard 7psi wastegate is being used, with a blitz spec R EBC). I can get an HKS 12psi actuator but its not cheap, around $380!!

He tried some extra springs on the std actuator which helped a bit, bit didnt solve the problem.

On the plus side, torque has risen significantly over the whole range, even with a 10-20kw lower peak power figure!

any help appreciated.

[Merli]

So you lost peak power as compared to the stock dump pipes?

Do you have a before and after dyno graph for us?

[SLY33]

yep i lost peak power with the better dump pipe. But this is only because boost dropped off.

We have pretty much hypothesised that with the new split dump, the combination of more flow through exhaust pipe causing more back pressure in the wastegate split pipe, which prevents the wastegate being able to close enough to hold boost at the top end.

Looks like im gonna have to give the HKS actuator a go. I will post the dyno graphs next week.