Apologies for digging this one up from the dead, but it is great information.

Twibs415 - Thanks for the back to back isolated change and validation, not often you see such clear cut results.

One question - are your power / torque figures at the wheel or at the crank?

I run a coldside twinscrew through a 2.5" exhaust, currently 285hp / 255whp. Looking into going up to 3" along with a better manifold.

If your figures are in crank hp then we are fairly comparable, if you are talking whp not so much!

It’s on a hub dyno. So “wheel”. Hopefully mid year I’ll have the car back up and running. New motor should be a little more tame but make much more power and be reliable.

Thanks for clarifying, I'm a little way off you then.

Good luck with the new motor hope it goes well :bigtu:

In addition to sizing considerations, what about coatings/wrap effects on exhaust efficiency? I've read that there are gains to be had. just ceramic coated my RB header and 2.5" mid-pipe. Heading to the dyno next week to see if there is any improvement.
This is on a C15-60 Rotrex supercharged 1.8liter NB1 engine. It currently produces about 200 rwhp.

I would be doubtful anything measurable, please let us know your findings none the less.

You were correct - no meaningful change beyond the normal variation I see from one session to the next. The header and mid-pipe sure look nice though :)