Question: Decat

[spike2002]

I have removed my cat from the 6 today as it needed abit of welding. i have noticed that the internals of the cat have been smashed out.
so what afects will this have on the performance as it oviously hasnt had a pipe welded in.

I know it should fail the mot but it passed last year like it

[Midnightclub]

If anything it'll give you gains! probably small but similar effects to a proper de-cat tbh!

[spike2002]

aslong as it wont lose power from it im happy

[Midnightclub]

People wouldn't de-cat cars if it did!

[samass]

id get a pipe welded in. the expanding of the pipe into an open box actually slows down gas flow, true, itd be minimal, but a straight pipe would be better for flow than for a pipe going into an empty box, then back to a pipe.

[ginge191]

i was about to say this ^^^^^^^^^^^^^^^^

you basically create an expansion chamber; which slows down flow; straight pipe of the same diameter throughout is the best for optimal flow.

[cwspellowe]

Correct, but pulse tuning is best for back pressure in an NA car, so the expansion chamber may actually be less detrimental to torkz than a straight pipe..

[samass]

pulse tuning comes into the game when you're looking at the mani and the each of the pipes (equal length, unirform radius, etc) going into the collectors.

the empty box would probably give you more low-mid range torque as the back pressure would be increased, where as the straight pipe would increase top end

[spike2002]

I am planing to eventualy cut it and weld a pipe in sometime the future but for now aslong as it isnt doing more harm than good im happy

[Midnightclub]

Tbh if the rest of the system was straight through it'd probably be good to give it some extra back pressure to increase midrange torque slightly