Is a 3 inch Downpipe big enough?

[MikeLMR]

when you change from one pressure and gas speed to another such as at the exit of a turbine, the interface is very crucial. If you look at an intake on a supersonic jet you will see an inlet diffuser that helps the transition from very high speed (high dynamic pressure) air to much slower but higher static pressure air. The same is true at the exit of a turbine where the gasses have been expanded through the turbine to a low pressure and are being vented back to atmosphere you can improve the efficiency of the turbine by carefully controlling the diffusion of the exhaust.

Reason you don\'t see it in drag cars ... they don\'t have the budget to exploit it?

[John Yorke]

Lots of cars running 400 with 3" exhaust, when tuning the yellow one it was decided the exhaust was the restriction - on went the 4" and saw an imediate increase, I think bigger is better

[Carl]

The exducer on a turbocharger is already designed to be pretty efficient.
That is the part that helps the turbine to work really well.
Of course everythiung can be improved on,but in the case of a turbo,there is no real need for an exhaust for it to be optimum.
Regards
Carl

[MikeLMR]

that makes sense then, didn\'t realise a turbocharger has a built in diffuser in the housing. Interestingly Greddy call their downpipes diffusers rather than downpipes.