the need for a 3" exhaust?
 

I currently have a 3" cobra sport system on my blob, running 420bhp.

The wife, neighbours and several tracks would appreciate it if I lowered the db level, and I have to admit I would'nt mind too as the car is getting used more frequently.

My question is, I also have a cobra sport backbox in my shed but its 2.5", and the box is more of a traditional shape rather than the round can type thats on it at the moment, how much is this likely to affect performance? The car is in for a map tweek soon as a couple of things have changed so it would be a good time.

I would keep the 3" centre and downpipe.

Is the internal of the 2.5" back box straight a through like a tunnel with perforations all around?
If so it will affect performance a little but not as badly as if it had a convoluted route to take through the back box.

I would guess you wouldn't see 420bhp after the map tweak, but it would still be very close...

FYI, easily getting 440/440 through a 2.5" ...... and its track friendly too.

Which system is that mate?

Yes, we'd all like to know. :thumb:

3" to 2.5" decat downpipe, to a H&S 2.5" back.

257 on an sc46 limited to 1.5bar.

I believe Andy Forest managed well over 500bhp with a 2-1/2" system.