[Tiz]

I live in Europe where we have less experience with (twinscroll) turbo setups. Therefore, I would be grateful for your thoughts:

My AT car has a 480hp rated GTX2867R (/w 0.82 AR twinscroll housing) but does not make enough top end power. It makes only about 350-380 hp (with high intake temps on the dyno) @ about 17 PSI using 93 octane. However, it generates torque and hp very early. About 300hp/ approx. 260 lb ft torque at 3300 rpm. About 9 PSI @ 3000 rpm. Highflow metal cat. Tomei Type 80 exhaust.

By contrast, my tuner has an MT FR-S that makes approx. 440-450 hp / 360 lb ft @ 17 PSI. This car uses a HKS 3040 turbo (/w a relatively small 0.76? AR twinscroll housing). Moreover, the car uses a header with a larger diameter and, probably, race cats. Tomei Type 80 exhaust.

(Btw.: My well-recognized tuner is still working hard on my car and there is no reason to complain. But I would like to do my own research or, respectively, hear your thoughts. I have converted the European number into US numbers (e.g. nm into lb ft). Probably, the measured numbers are not whp numbers but were already converted/standardized to crank hp.)

Now my questions:

1. What hp rating would you expect from a GTX2867R? At what PSI?
2. Why is it so difficult to achieve the rated 480 crank hp (or at least 400-450 hp) without using race fuel? (My Subaru STI made 490-500 crank hp on 93 octane using a 525hp rated GT3076R.)
2. Is there any reason why an old HKS 3040 would make more power/is easier to tune/produces lower intake air temps than a 2867R?
3. Do you know what diameter FRS twinscroll headers (for high hp applications) normally use?
4. Does an AT suck much power?
5. Any other thoughts?

Many thanks!

Tiz