This lifan build will book with the right gearing. With an 80% drive efficiency (not that great) if you jackshaft, you will have 6.8 hp available at the wheel. Lets say you weigh 200 lbs and the bike weighs 130 lbs, you should go about 61.5 mph with proper gearing and sitting upright. If leaned in, 69 mph is possible with the right gearing. You'll probably have closer to at least a 90% drive efficiency with it running on the left side with proper alignment, so more around 7.65 hp to the rear wheel. Lets look at the same 200 lb rider and 130 lb bike. You can now go 64 mph upright and almost 72 mph leaned in, once more, with proper gearing. So this engine can move a decently heavy person and bike to 70 mph. Not sure why folks assume 50 mph to be the max speed of an 8.5 hp 4 speed...