In standard form the TY175 is rather under-powered and seems unwilling to rev very high. Over the years this has led to various alterations to improve power, but seemingly carried out without much attention being paid to the root causes of low power output and lack of revs. Very poor air-flow through the stock induction system and porting better suited to a smaller capacity cylinder than 175cc appear to be the 2 main things which compromise the performance of these motors.
The most effective single alteration that can be made to a 175 is an uprated competition intake system. This is an upgrade which needs the frame to be modified so a large volume competition air box can be fitted and is certainly much more involved than simply boring cylinders out to accept a larger piston, or fitting a low volume replacement air-box which retains the very restrictive stock intake hose.
Large volume 175 air-box
On otherwise completely standard machines fitting a large volume competition air-box and properly jetted 26mm carb will significantly improve performance and for many riders this increase in performance will be all they need. For riders competing at higher levels and for those wanting to the ride the easy route in modern events , further changes can be carried out.
Removing the bottleneck of the stock induction system provides the potential for considerably more power/torque from the 175 motors. Porting changes and replacing or modifying the stock reed block is the next stage in the process and will mean a far more competitive bike, which is as reliable as a stock machine and much more fun to ride. We have now made changes to our porting specs first tested almost 3 years ago and the latest ones provide even more smooth, tractable power.
It is worth bearing in mind though that performance potential will be reduced considerably if your motor is badly worn, exhaust is clogged or poorly designed, or you have a sub-standard ignition system fitted. Essentially all these things need to be sorted before seriously thinking about performance upgrades. Replacement air-boxes which retain the stock intake hoses might possibly improve flow very slightly. The very small convoluted intake hose will drastically reduce potential flow, so this needs to be replaced with something more effective if you are looking for increased performance.
Stock 175 air box
In a nutshell its possible to carry out modifications on a TY175 motor which make these little bikes very possibly the most competitive twin-shock machine available! However, without a carefully uprated induction system as the first step in the upgrade process, then forward progress will be very difficult and rather than simply a gutless wonder 175 you may well end up with a VERY expensive gutless wonder, which is also rattly and unreliable!