Exhaust Theory?

[Poodle]

Yeah but tbf Poodle, they're running 12-13:1 AFR @ WOT... Diesels are running 17-18:1 AFR to keep smoke levels down, even more at stock calibration...

Diesel needs more air for a given power level. That's why a 90hp Diesel has the same size exhaust as a 167hp GTi6.

Yuuuuup, hence why i said what's good for a 300bhp petrol should be adequate for up to 180bhp on tuned diesels. If you don't believe me go and look at the exhaust on the 250+bhp BMW 30/35D engines, and that's bearing in mind they're packed with restrictions.

The point is at stage 2, like what JTaylor is aiming for, anything over 2.5" is unnecessary, expensive and heavy.