If you're on a tight budget then you can make noticeable improvements on the 28 pipes.

As has been said, the washer in the header needs grinding out from the strangulated 30mm to the full diameter of the header. Then look through the silencers and you'll see they too have a restriction, but this is harder to deal with and just fitting MC18 or 21 silencers doesn't strictly work as the mounts are in a different place.

We will be revising our pipes very shortly. We're in the process of doing the RGV and Aprilia right now, and will be moving on to the NSR250 once they're done. We're now using full cone technology and not stampings so accuracy is improved and thanks to this we can pretty much get the pipes to go where ever we want without spending a fortune on different stampings. However, the issue on the NSR is that for good performance they like a big belly section which is difficult to route, but we've managed considerably more clearance on the RGV and Aprilia, so I'm optimistic that the NSR can be done too.

We won't be making specific 21 or 28 pipes. One size will fit both. Once they're done we'll look at fiddling them to fit the MC18 too.