Two stroke pipes, are such a complicated thing, that it is pure mind boggling at how different they need to be for every single engine build. So complicated, that when you build one & it matches up to the porting & build of that engine, the power that engine will produce, you'll be amazed.
But, just because that pipe built for & matched up to your engine worked like it was suppose to, dont mean you could sell that pipe to someone & it would work the same on their engine build.
That engine that the pipe worked so well on, when you change anything about how that engine is set up, even no more than fitting the next size larger piston, it causes the engine tune to be off some amount with that pipe, because you changed the bore size. The difference in change might not even be enough for a rider to tell or feel the difference, but it is there.
Building the engine, only part of what all has to be done & everything that has anything to do with the engine must match up, from the tip of the air filter element all the way through to the tip of the silencer outlet.
Getting a cylinder ported, like when your building for top performance, if that is all you've done, is compared to like one ant from a large ant nest.
It might be surprising, but there could be times on an engine build, even using the OEM 250R cylinder, that a larger stinger would be needed. All about that build & what the engine is being used for.
Neil