[Laird Scooby]

Reducing the exhaust efficiency of any vehicle by constricting it with DPFs, cats and other things will make the engine work harder which means it uses more fuel to do the same work.

I remember as a kid i'd somehow got hold of some American car brochures (a long-distant relative of my mums brought them) and was looking through them and found that coincidental with the mandatory introduction of catalytic converters, not only did power and performance suffer but the economy suffered badly too.

Back then i had no idea what a cat was except the four-legged furry thing that came in for a feed, slept then disappeared on a 4-5 day tomming session.

It was only later things dropped into place when they decided our cars had to use the things as well.