guys

at the moment i have got a 3'' decat downpipe a 3'' decat centre and a 3'' backbox with a 5'' exit pipe and if i am honest it is too loud for my taste (no offense to others) due to the 3'' bore i can not replace the backbox with a samller exit pipe to reduce the noise or fit a centre cat to reduce the noise and emissions as standard/afteramrket systems are 2.5'' bore to my knowledge.

and obviously it will fail its mot as well come feb

my trouble is i dont want too much of a power decrease but i appreciate that i will end up anyway.

i need some pointers do i feel i have 2 choices (any others will be welcome)

1) replace the down pipe with a standard cat downpipe then run a decat centre and a back box of my choice
2) replace the decat down pipe with a samller bore ( i am aware of a 3'' entry to 2.5'' exit decat downpipe) and then fit a centre cat and backbox of my choice

which will give me the best power output?

and also the car has been remapped for both decats if i fit one of these cats will it cause any harm to the mapping or will it need doing again as i dont want to cause any harm to the engine etc?

please some advise is needed

many thanks

steve

also when this is done anyone interested in the above system?

 

If you make any major exhaust changes (cats/bore) you should have a remap.

Is it too noisy full stop? Or just motorway etc? As i had a bung (£35) made for mine, which i will use for motorway miles, makes a big difference.

Most of the restriction is in the downpipe cat, so replacing that will drop the most power.

Depending on your car and other modifications, a drop to (standard) 2.5" bore shouldn't give any real noticeable power decrease.

 

This may seem like a stupid question but whats a bung?
Where does it fit?
Can anyone get one of these bung's?
I've got a 2.5" decat system with a 6x4 oval and i find it's too loud.
I keep meaning to record the sound inside the car and post it on here to see if it's normal.

 

Exhaust bung. It fits in the tailpipe, taporing the exit. My 4.5" Ninja with the bung in, is about 2" exit.

Contacted Hayward & Scott, with the dimensions, and i'm sure they can make you one. Mine was £35.

Did make a difference to the noise. But they're not recommended if your car is mapped, unless you use low boost (if available) or stay off boost.

 

if i was to replace my exsisting system with a 2.5'' bore but so a (decat down pipe, decat centre and a hayward and scott back box) keep it as a double decat woudl i need it remapping just because i have reduced the bore by half an inch?

would this cause any damage or fueling issues to the engine

thanks

steve

 

As i said before, any major changes to the exhaust and a remap is advised. Especially if you're reducing the bore, ie. restricting the flow.