3" Or 3.5" Cat On Stock Exhaust

[Robos F6]

I have a BF F6 and I am just wondering whether I would be better off getting a 3.5" cat rather than a 3" cat to bolt onto the standard dump. I know the standard dump is 3" but I was looking at getting a 3.5" cat with a 4.5" body. Obviously the bigger cat would flow more than the 3".

[Bender]

just get the bigger one and be done with it. Saves changing it later if you go for more power

[Redback]

you said it, the factory dump is 3". Just go a 3" with a 4" body if its comparitively cheaper. If we're only talking about $ 50 difference mate fit the larger one. Just make sure that they are 200cpsi and not 100 if you want to stay legal. Otherwise you might just aswell have punched your cat out. I've got a 3" cat on it at the moment and it's flowing the kind of HP I want. At the moment it's mods like a ported wastegate and actuator that is holding me back and not my 3" cat. It depends what your target HP is? IMHO don't waste money on a system that handles 400rkw + if you never intend to push it to that.

[Benny-4000]

you said it, the factory dump is 3". Just go a 3" with a 4" body if its comparitively cheaper. If we're only talking about $ 50 difference mate fit the larger one. Just make sure that they are 200cpsi and not 100 if you want to stay legal. Otherwise you might just aswell have punched your cat out. I've got a 3" cat on it at the moment and it's flowing the kind of HP I want. At the moment it's mods like a ported wastegate and actuator that is holding me back and not my 3" cat. It depends what your target HP is? IMHO don't waste money on a system that handles 400rkw + if you never intend to push it to that.

I was told by a exhaust workshop that if you get canaried fro a suspected punched cat in Australia, there is only two ways that they check it.

1. They disconnect the exhaust from the engine or turbo and poke something down it to check that there is something installed in it.

2. With the car running, they measure the temperature of the exhaust before and after the cat and look for a difference. If there is no difference in temp, they assume that there is no brick inside the cat. A 100cpsi cat is still definately a restriction and therefore would still cause a drop in temperature across the cat