You will need the high nitro pipe. These versions have a greater volume than the low nitro equivalent. I had a high nitro pipe for my OS Hyper 50, fitted to a Raptor 50SE.
Once fitted, you will have to lean out your engine by a surprising amount in order to get the pipe working efficiently. Be careful here, as if you over lean the engine you will damage it. You may also notice that your engine will get warmer than before, generally this is OK, but if it gets too hot then you know that you’re almost certainly too lean. Also use a good quality fuel, that way if do have a lean run you’ll stand a chance of getting away with it...
Although the pipe was supposed to have a fairly broad rev range, I found that unless I tuned it for maximum power, it was a bit peaky. This also made it a bit of a pain to use with a multiple head speed governor set up, but fine if you just aim for the peaked-out head speed. In my case this was around 2000RPM on the Raptor 50, with an 8.5 gear ratio and OS Hyper 50 engine.
In the end I fitted a tuned muffler as I found it less difficult to manage (i.e. keeping the mixture spot on), and also I wanted to be able to achieve a lower head speed without any peaking.
My 50 pipe did generate a lot of power, and when on song produced a very clean engine note.
Hope that this is helpful!