100 cell cat and twin vs single centre pipe

[faaaaast]

Well according to fluid dynamics even though 2 x 2.5 has a greater cross sectional area the transition from one to two pipes causes fluctuation in gas flow and the y-point can become a bottle neck

A single 3" keeps gas flow at a constant high speed and there is no bottle neck.

In the clear light of day, and after a few hours sleep, I recall seeing a nice attempt to fix this issue. It was from a custom exhaust place in Scotland somewhere I think. What they'd done is while constructing the Y-piece, they'd inserted a metal 'blade' just before it to 'split' the air in half before it actually hit the Y. Looked like a nice bit of work to me!

I'll try and find a link...

I'd *guess* that once you come down to it, the two designs won't end up being that different in terms of overall performance, as both advantages/disadvantages probably end up cancelling each other out. The only other advantage to 2x2.5" pipes is you shouldn't get so much of a 'boom' factor; low resonant frequencies are far more difficult to damp than higher ones.

James

[S-Express]

Guys has anybody confirmed an S2 will pass an MoT emissions with a 100 cell cat?

Also what is the think is 1 3" pipe better than 2 2.5 inch centre pipes?

Looks like i'm going to have to remove the sh*t that was put on the Avant to get it through an MOT.

Can't be doing with this problem every year.

Just been talking to John Glover at PipeWerx (as he's doing me a system on tuesday
) and he reckoned a single 100 cell sports cat will pass the emissions no problem.
Had my mot today and although car failed, the emissions were absolutely spot on, not bad for 160k miles and original cats
When I see him tuesday I'll ask him about pipe diameters.....

[Acidburn]

This was one of the reasons I got the year s2 I did so I did not have to worry about the cats.

I plan on removing the y section and just running one straight pipe which should also help on weighing less as well.