I've just bought a MK4.5 1.0 and would like to fit a dual exit.

Would an ST backbox fit a 1.0 with a reducer pipe? It does look very similar in photos.

It's purely for looks although a small rumble wouldn't bother me too much.

Thanks

Can't see why not, you would, obviously, need the rear pane from an ST too.

If it's got an active exhaust valve though, I struggle to see how this would work, unless you could link it to "Sport" mode, you may have to remove it or force it open

The ST backbox capacity may be too large for a 1.0.  Could end up with exhaust gasses cooling before exiting and causing some flow restriction.  Have you checked prices for a custom stainless backbox instead?

1 hour ago, DaveT70 said:

Can't see why not, you would, obviously, need the rear pane from an ST too.

If it's got an active exhaust valve though, I struggle to see how this would work, unless you could link it to "Sport" mode, you may have to remove it or force it open

The Mk4 ST has never had an active exhaust. That was only the MK3 RS and MK8 Fiesta ST (and Mustang).

1 minute ago, alexp999 said:

The Mk4 ST has never had an active exhaust. That was only the MK3 RS and MK8 Fiesta ST (and Mustang).

There you go then

Good to know, looks like a reasonably straight swap for a fitter.