Originally Posted by E.Marquez (Post 404430)

Originally Posted by Stephan (Post 404428)

rktdoc:

My POV is, that building the engine is quite complex with lot of things you have to solve. You need to start with correct cams, headwork, HC pistons, full exhaust, and build it info functional package ending with correct setup of carburation and air intake as stock airbox is true limitation (which is the problem I am still facing, but there is some progress). You will be quite lucky and will do big amount of work if you will success, and result will be not only engine with good top power, but engine with nice powerband.

Ovebore valves or 100mm pistons are just icing on the cake, affecting that you have 1-3 bhp more.

Originally Posted by rktdoc (Post 404437)

Yes I'll not dispute that logic.
I build race engines regularly in my shop, I'm pulling 90-95hp out of single cylinder normally aspirated atv engines. This engine just as many of the Honda four-stroke singles of that time period the biggest thing limiting power output regardless of airbox is the cylinder head port design.
Without welding up and actually changing the ports the best possible scenario is to improve upon the flow of the stock design in every aspect.