Exhaust Theory?

[todd1983]

For what its worth

I'm running a homebrew 3 inch downpipe to 2.5 system with 1x barely restrictive backbox

Thats with about 240bhp

Is it restrictive? Maybe, maybe not. Be interesting to dyno with and without the system connected.

It has crush bends which no doubt take it down to nearer 2inch in places

One day I'll have them cut out and replaced with mandrel.

I would have thought a 3inch downpipe to 2.5 inch unrestrictive system would be fine for near 300bhp on a diesel - but am keen to see some real world evidence to back any of this up.

I have 3" into 2.75" downpipe on my 330d with 285bhp