The high claims for special exhausts are something that I take with a pinch of salt without back to back Dyno data.
As you can imagine I have some info on this from George Braly, one of the few folk who has actually done a fair bit of Dyno work on Piston Aero engines, and quite likely more than anyone else on the planet.
His discovery for several exhausts on NA TCM 6 cylinder engines is the torque peak moves around a bit, so at a particular RPM you get a small gain but lose it say at 2700.
When asked he refers people to the guys who buy up all the NA exhausts of Cirrus and Beech that buy them from TAT when they do a turbo upgrade.
Read between the lines
For Turbo engines all the best gains come from intercoolers and ones that are engineered with higher efficiency. Every turbo should not just have one but a good one. Problem is most will never get one coz the cost of paperwork and R&D.
Cheers
PS if Walter and JD wander past they might have some good first hand info to share.
