Funny enough, I would like smaller end pipes!! Nige, out of curostiy why has the MV got no back box when the milteks do!?
Well firstly smaller end pipes are not a problem - we can change the 90mm for twin 76mm if required for you.
With regard to the rear section - it's all about maximising the gas flow rate.
Here's an image of the Milltek rear on our MK 5 when we purchased it -
As you can see the gasses are diverted all around the boot well and then into a baffled silencer - great for reducing sound - not so great for releasing pressure on the little KO3 after mapping.
We introduce a straight through silencer at the front of the system to negate the need for a rear transverse silencer at the back. This way the pipes can run fluidly without hindrance right from the turbo to the back of the car.
Cheers
Nige