Exhaust A/R size change?

[grepin]

Hi I am wondering for my 2835Pro turbo wether it would be worth going to a larger exhaust A/r if my current .64 A/r has huge amounts of back pressure. I have a hI flowing dump fitted however I am unable to hold the wastegate (internal) shut in the high rev range. Have a 20psi actuator fitted. Measured inside the exhaust housing pressures close to 40psi. Tried various boost controllers.

Thanks

[RS500]

on what engine?

[grepin]

on what engine?

RB25 with Greddy plenum, exhaust manifold, RB25 Head with HKS Cams and larger calves, 3.5inch exhaust, has made 300rwkw with dropping boost due not being able to hold the wastegate shut.

[RS500]

what kind of boost do u run?

well according to HKS, the A/R .68 exhaust housing is the one suited/recommended for the RB25 (check link below), but given that you have so many mods to your intake, cams and the larger valves, it seems that the engine is producing too much gas flow which the .68 can't handle (or maybe even the 2835 turbine wheel), therefore you might need to go up to the A/R .87 which is available for the GT2835 Pro S.

http://www.hks-power.co.jp/products/turbo/...o/ac_gtpro.html

[RS500]

also, don't forget that the HKS GT2835 Pro S is only rated at 420ps which you are already producing at the rear wheels, so it might be running out of efficiency.