Is there any BHP Difference in a closed necked/open necked D/pipe ?

If not why two options ?

 

I changed from a 3" closed neck to a 3" open neck and could definitely tell a difference. You only have to look at them together to know that the open neck will flow better.

 

Closed neck - cheaper and easier to make. Blocks off wastegate flow, causing turbulence which spoils turbo spool up (ie turbo needs more revs to start working), also limits total flow and hence reduces peak power.

Open neck - tend to be a little pricier. Almost always much superior for power, spool up etc. Open tends to mean "bellmouth" (one big oval pipe), but also good is twin dump (separate pipe for the wastegate flow). Lately it's getting common to see a splitter in the downpipes which further reduces turbulence between exhaust gas coming out of the turbo and gas coming out of the wastegate.

Which is better out of twin dump & bellmouth? The debate has caused interesting disucssions, but either is going to be a big improvement on the closed type.

 

Hades, Do you mean completely,or just diverts it into turbo exhaust gases?

 

Thanks Mr Contro + Hades, why does any maker bother making a closed neck ?

 

for the reason hades pointed out... price

 

It blocks it after about 20mm, so the gas has to go round a right angel bend, into the turbo flow and then round another right angle bend down the downpipe. It is where it crosses the flow coming out of the turbo that you get the real turbulence problems.

Closed neck is cheap as it's easy to make. It is just a bent piece of pipe and a flange, as opposed to a taper or other more complex shape.

 

Thought that may be the case, cheers mate.
Does the standard cat pipe have a closed neck then?

[Edited by matty01 - 3/16/2003 11:00:39 PM]