downpipes - anyone flow tested?

[matress]

hey guys,
i'm just wondering about the differences in flow between a 2.5" dump pipe with 3" front pipe compared to a 3" dump pipe and front pipe.
has anyone actually tested it?
i've read a lot of write-ups stating that 2.5" is more than adequate for TD05 type turbos and that 3" is overkill, but there hasn't been any data to prove it.
comments?
cheers,
Mat

 

[Entaran]

From a purely non-scientific point of view, having a 3 inch inlet on a 2.5 inch outlet creates turbulence in that the gas leaves and has to travel horizontally to fill the vaccuum area of the pipe.

It should run better on the 2.5inch turbine outlet with a 2.5inch connection and gradual flare to 3.

 

[bazeng]

i've been told that when the gas goes straight out of an exhaust housing, the spiralling effect of the gas is not a good thing as it slows down flow.. to break down that spiral, a good technique and proven technique is to step it out harshly to say a larger diametre, this breaks the spiral and sends the gas out towards the muffler faster...

i personally dont know whats true / false..
but the more flow you can give your turbo, the better in my opinion..

try 3", if u cant get it go 2.5"..
also what do u want to spend and also how does the wastegate intergrate with the rest of the exhaust?

 

[Entaran]

From a physics point of view that doesn't make any sense baz.

 

[Rockabilly]

I made a new tapering dump today. 63 to 76 in the bend. If you only use
lowish boost, 63 will do for the whole exhaust bar the cat should be 76.
I intend to run 17psi tho. So 76 for 3/4 of the car & 70 for the last part.

 

[EVO-00X]

:lol: Stick with the same size all the way through. Reducing or enlarging only creates unnecessary turbulence :wink:

 

[matress]

i'm not sure if i worded my initial question properly...
is it going to make a big difference if the front pipe end of the downpipe is 2.5 inch and then expands to 3 inches on the front pipe compared to the end of the dump pipe being 3 inch and then a 3 inch front pipe?