Thumper Racing don't quote any power figures in their advert - see http://thumperracing.net/index.php?route=product/product&path=37_43_288_107&product_id=98
My experience is that it transformed my TTR but, tipping the scales at over 18 stone , I need all the extra oomph I can get - I even manage to pull an accidental wheelie occasionally
If yer want to make the bike easyer to ride in the tight woods sections put a Rekluse EXP auto clutch in it.... The YZF/WR250 unit drops straight in...