The larger displacement engines seem to have a problem with taper through the 10.5cm housing. Either try radically hogging out the stock 10.5 housing, going to a larger A/R Australian housing, or putting out the cash for the prototype dual-gated TS tubular stock manifold from ETS.

 

Tom - I believe I read somewhere else that you were running an MBC. If you are using the ECU to control boost, I would suspect you could hold 35 psi across the rev range without a problem.

 

I said this earlier a real good EBC will hold boost all the way thru. The HKS EVC VI will hold whatever target you set it to thru redline. It can also drop off if you set it up that way. The Greddy Profec II and AEM Tru Boost are digital MBC's basically and will hit a set boost and tapper off like a MBC does and thats why they are cheaper then the HKS as the Greddy goes for average 350-375 shipped new and the AEM Tru Boost maybe 250 and the HKS 575+.

 

I reread your initial post Mauri and I believe that the boost taper you are experiencing is normal for the IX 16G turbo configuration. I think that the taper can be remedied or significantly reduced by porting the turbine housing.

Also, I have an FP Green turbo sitting around here that doesn't taper or creep with a fully ported turbine housing. We could swap this Green for your IX. Let me know. Or else bring or send me your turbine housing on TICA Bus and I'll port it for you.

Shoot me a PM.

 

boost will always taper you have to get a up graded waisgate

 

So, Mauri, I am still wondering where exactly your external gate is sourced from. Is it flanged onto the exhaust manifold, or is it sourced off the turbine housing, the O2 housing, etc.?