UK version of VW Polo gets lower MPG due to different exhaust routing

[MetroMPG]

Found this interesting tidbit:

Right-hand-drive Volkswagen Polo diesels will have slightly worse fuel economy and higher CO2 emissions than the left-hand-drive versions sold in mainland Europe.

This is because the oxidation catalyst and diesel particulate filter in the exhaust system have been moved... [to permit the switch to right-hand drive].

The figures given for the 1.2 L diesel are:

• 90g/km of CO2 for right-hand-drive in UK
• 87g/km of CO2 for left-hand drive elsewhere

(CO2 is proportional to fuel consumption.)

I wonder just how convoluted the UK exhaust routing had to get to have a measurable effect on fuel economy?

Source: http://www.whatcar.com/car-news/vw-p...iciency/244512

[Daox]

Pictures would have been so nice.

[tjts1]

Diesels are very susceptible to changes in back pressure.

[Old Tele man]

...didn't know that diesels could get "constipated"

...I've learned something new today.

[Frank Lee]

OK this is my WAG but I suspect "backpressure" is not really a factor; they are talking emissions which include cold start and thus the distance from cat and filter to engine is critical for their heating-up phase.

I suppose if it was more involved that merely shuffling the cat and filter around i.e. if they made them different and less free-flowing that could explain it too.

It would be good to know if these measurements and differences are due to cold start or steady state.