I think I can add some useful info on this subject... 1) Indeed a 125cc will not have 30hp if you "derestrict" it, that was only the case with some powerful 125cc 2stroke bikes back in the days, like a Husqvarna 125 that had up to 35hp... Still most 125cc bikes are restricted though I think, because they can't have anymore power than 15hp exactly, so that engine will always have a little more in it I assume. You won't get more out of it than a few hp tho, like 1-3 or so but even that is not bad for a (light) 125cc bike. Another, more open exhaust (or with silencer removed) will not really make a difference on a 125 bike I think, now I did that on my own bike and I don't feel a notable difference. 2) 4Stroke bikes are slower/less powerful than the older 2stroke bikes however there are some aftermarket parts, mainly cylinder kits that can make your 125cc 4stroke bike go real fast as well. Malossi and Daytona for example make 180cc cylinder kits for a lot of models that reach like 28bhp. It can be a good option/investment if your 125cc bike is pretty slow... Here you can find some info on supported models/bikes etc: https://www.malossistore.eu I own a Fantic SM125, 2019 model and it's a very light and fast 125 bike by default, despite it having only 9.7kw instead of the max 11kw that most 125cc bikes have, which is the max allowed in that class. Another rule says you can't have more than 0.1hp/kg, and this bike is very light (96kg) so the power had to be limited. I'm having it derestricted now and I'm curious what the power output will be, I'm sure it will add some nice power since it's a powerful engine and already accelerates nicely. 3)