De-Cat or not De-Cat???

[BigD]

I was genuinely curious.

cut and paste . . .

As well as the gas physically flowing down the exhaust, there's a sound wave generated as the valve opens. By stepping up the diameter of the pipe, these sound waves can be made to reflect back and form a standing wave. If the low pressure part of the wave is arranged to be at the valve opening, it will help suck the exhaust gas out. The challenge is to get this to work over a large RPM range and is often achieved by having several points of refection, i.e. primary collector, secondary collector, and system.

Fitting a Cat will set up a refection but, as it is fairly well down the path, it is likely to be more noticeable at lower RPM. In my case it is out of tune at 4-5K RPM and causing a loss of power.

But my point was that a CAT does not effect power by restricting the flow, but more by altering the tune of the exhaust. By removing it, you could reduce the power or change the characteristics of the engine's response.

Clever stuff then.

[a4drk]

Dom,
I bought a Larini sports cat for my S2 Exige - 200 cells instead of 600 on OEM
"supposed" to give it an extra 7bhp
sounds good tho......

I've bought a performance manifold on USA Ebay - getting it delivered to the house im staying in Florida ! -
coming back in my suitcase..... !

It comes with a de-cat pipe, but i dont think ill fit it

David

[2F45T4U]

Thanks for posting the dyno runs to remove any doubt!

interesting to see.

You're right in saying a well designed cat' is fine. There is no doubt that where a cat' is too small or choked it will choke power, but this is so rare these days i feel the whole de-cat' thing is a bit of a forum myth..

I de-cat'd my k-series S1 years ago but it resulted in little more than a horrible resonanant drone at 70mph. Needless to say the cat went back on and hasn't been off since.

Fraser

[martins]

Yota lump with a 2ubular re packable back sports box. Have a cat pipe with no cat. Blew most of it out one day at KH and then the remainder in my garage. Also have a 2ubular sports cat pipe. Run the non cat pipe most of the time just for the pop it make when changing from 2nd to 3rd and 3rd to 4th when overtaking slower vehicles. Childish I know but you have to have small pleasures in life. If anything I would say slightly quicker without the cat and I can rest easy that come Oct I can switch boxes and pass my Mot without having to fork out £400 for a new cat..M

[smoo25]

I'm just glad I wasn't the lowest on day!