I have recently corresponded with Chris from HPF about the boost mod:
-me
> >Would I benefit from this mod if run with the following setup?
> >K&N intake
> >Greddy type R bov
> >HKS exhaust cam
> >TurboXS mbc
> >Greddy PE exhaust
> >SP downpipe
> >Greddy BCC
> >RPS stage 2 clutch
> >TTC mod
> >EGR mod
Chris
You'll pick up about 30-40 rwhp. You'll want to put your turbos back in sequential. After you do that you will wonder why the heck you had them in parallel anyway.
I have this mod on over 30 Supras, none have had their turbo's fail yet. That's probably around 70 years of cummulative driving with the mod without a failure.
Most people get 325-350 rwhp on the 1st turbo at 3,000rpm. Then a quicker spooling 2nd turbo and more power through to around 7,000rpm. Try it. If you don't like it, switch it back.
Later,
Chris.