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Hi Flow Cat


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if your present cat is restrictive (blocked/choked and/or small diameter) then yes you should replace it with a 2.5" cat. if you already have a 2.5" cat, performance gains by upgrading to a 3" cat would be negligable, i imagine.

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  • 2 weeks later...

Yeah when my stock cat blew up ( hollowed out itself on the track) i got a hi flow 2.5" one put on. Lowdown torque is increased slgihtly because its more free flowing. When i had the cat replacement pipe on however! the thing just took off, even high flow cats restrict heaps, and creates totally different sound!

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Measure the exhaust back pressure before and after the cat. That will give you a good idea of how much total exhaust restriction is in the cat, and how much across the cat back system.

Only then can you make a logical decision on how good the cat is.

If you work on the basis that each psi back pressure is costing you 1% power, that is a good rule of thumb to work with. Realise though that noise increases faster than power when you unblock the exhaust.

Probably about 10 psi is reasonable, and 5psi is very good indeed, but you gonna have trouble with the cops if you try too hard.

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