Thumper Racing Kit - Abused

Thumper Racing Rincon 702Big-Bore Kit Price ListPiston kit (rings, clip and pin): $185Gasket kit, head base and tensioner: $50Bore cylinder: $49K&N air filter: $59.95Moose Power Commander: $339.95

A bit sluggish is an understatement when it comes to the stock power of the 2006 Honda Rincon 680. In the September '06 issue of ATVR, we conducted a long-term experiment with the Rincon and fell in love with its handling characteristics as well as its comfort. I proclaimed that even with the addition of a lighter and extra-horsepower-producing pipe, the Rincon might still be a great candidate for some motor mod surgery. Finding a reputable company that could build a dependable motor would not be our only difficult task. Because this new 680cc motor was fairly new, no one had yet tackled this feat. Luckily for us, Gary Hazel, owner and operator of Thumper Racing, stepped up to the plate and transformed this lazy Rincon into a flaming beast of fury.

Since reliability is very important for us, Hazel decided that increasing the displacement and compression ratio would be the best way to grab ponies while preserving its dependability. The stock motor has a bore of 103mm, giving us 675cc and a compression ratio of 8.5 to 1. Being that this kit is a bore-in kit, no sleeving is necessary. Hazel supplied the specs to Wiseco, which built a flat top 10.25 to 1, 104mm piston that raises the cc from 675 to 702, can run on pump gas and prevents the motor from overheating. Since the '06 Rincon has EFI (electric fuel injection), the Thumper kit contains a Moose Racing Power Commander system that plugs into your laptop for the purpose of reprogramming the mapping and fine-tuning your fuel injection. No reason to wig out: Hazel claims this system doesn't require a rocket scientist to dial in.

Finally, it was time to blast some trails and discover what this transformed Thumper Rincon could do. Almost immediately, I knew the magical hands of Hazel and crew had performed a miracle. As I pulled away for my first ride, I stabbed the throttle and up came the front of the Rincon, a feat which would have been nearly impossible before. While blasting out of berms, turns and up hills, I could feel a massive improvement on the bottom to midrange power. Through wide-open trails, the Rincon felt like a new machine as I let it all hang out. At high speeds, the motor pulled harder and longer than what I could remember from the stock machine. I yanked the airbox lid after about 30 minutes and gained a few more horses (be careful not to allow in mud, water and grit if you follow suit). And to top things off, our rigorous testing proved that this rebuilt engine remained rock solid and dependable with the installation of the new Thumper Racing big-bore kit.-Thad Josey