Exhaust Question

[Louie_D]

Is it ok to go 3" outlet on the extractors into twin 2.5" or is it better to keep it the same all the way threw?

[davomcd]

Going from a 3" diameter to 2.5" diameter at the flanges would cause a flow restriction... exactly how much of a restriction i.e. HP loss I don't know.

Better off keeping them the same size.

[RB30X]

If the extractors and cat flange 3" and steps down through the cat to the 2.5" twin system it shouldn't be too bad. The exhaust gets cooler and volume drops towards the rear of the car.

cheers

[Mungrel]

It would be better to keep it all the same diameter, however there's no reason why you couldn't fit the extractors and modify the cat pipes at a later date (if you choose to)

[Louie_D]

if i was to go twin 2.5" all the way, what sort of power would the car have to make before it would require a twin 3" setup to deliver the extra horses? I dont want to sacrifice to much down low power for top end but i want to have the car flowing. I should mention my aim is 300rwkw in the future so will twin 2.5 all the way be ok for this sort of power?

[drg86]

I'm currently running 3" outlets into 2.5". No problems, just have a merger before the cats. It would be better to go 3" all the way.

Something to consider is the price difference between 2.5 and 3". In my case it was $80 to get cats opened including the 3" mergers, or was quoted $780 for 3" metal cats. Decided the extra $700 was better spent on the tune.

300rwkw is around the mark you would probably be better off with 3". I'm sure some of the forum sponsors would be able to give you a definate answer.