Last Saturday we continued our Monkey development and took it over to the Dyno at Performance ATV, Inc. here in Miami. The guys over there are seriously cool dudes and have a conveniently located Dynojet 250ix that we're able to borrow for a couple hours when we need to throw down some numbers. This will be considered our "Stage 3" Package.
The shop Monkey is equipped with our prototype intake system, our 13:1 high compression stock bore piston, a TB Parts camshaft, and a Yoshimura full exhaust system. We loaded a base map the night before and put some miles on it going purely off of feel so that we could start to seat the rings in before the dyno session in the morning. For the hell of it I also threw the Dragy on and did some 1/8 mile pulls with the stock gearing and base tune.
Around 11am we got it strapped down and did the first couple pulls, only to find it was insanely lean, producing an underwhelming 11whp (A bone stock Grom on this dyno does 8.3whp). After about a couple hours of pulls and revisions we settled at a comfortable 13.7whp with a clean AFR pulling up to 11,000rpm. The graph below shows the base map versus the final tuned map.
When we dyno bikes we like to run the stock gearing as well as the recommended tire pressure, so we showed up with 15/34 gearing with the tires set to 32psi. After the dyno session I swapped the front sprocket to a 12t and went back out with the Dragy, and we dropped .77 of a second off of the ET and picked up 3.79mph in the 1/8th mile!
Overall, the bike is much more enjoyable to ride. It really didn't lose any low end in comparison to the stock bike as shown in the graph below, and it picked up a TON of mid range and top end.
The camshaft generally moves the power to the right, but the high compression piston helps to make up for the bottom end that sometimes is sacrificed with a stock piston paired with the cam. At the end of the day we're satisfied with a 65% increase in WHP over a bone stock bike, with fairly minor modifications!