Re: 9.9 Yamaha or honda question
Modifying a 9.9? I thought this was a joke, but I'll bite anyway.
<br /><br />Any performance advantages in modifying the exhaust valves or the exhaust ports on a 4-stroke 9.9 is overcome by expense. Hardly worth messing with it. <br /><br />2-strokes
can gain additional hp by modifying the exhaust ports. But this usually means modifying the tuned exhaust system, the rest of the cylinder transfer ports, and increasing carb jet size as well. Your upper rpm will increase and usually you will lose some lower end torque. Noise will be related to the tuned exhaust system modification. Fuel consumpiton may or may not change, it all depends on the engine and its use. Your chance for a lean condition (detonation or burn down) increases. The chances of increasing a 9.9 hp by a few more (to 13 hp) with just an exhaust port mod is unlikely.<br /><br />The engine would have to be disassembled and the cylinders would have to be modified using a tool similar to a dremel tool. Transfer ports get enlarged, smoothed, and re-chamfered. Porting is usually done by experience, and can really screw up an engine if done improperly.<br /><br />The only advantage the 2-stroke Yamaha would have over the 4-stroke Honda is 10 lbs and less initial cost. But it only comes in a 15" shaft. The Honda and Yamaha 4-stroke 9.9's come in 15, 20, or 25" shafts.<br /><br />
"Remember -HONDA- has been building 4 strokes for a long time and has buy far the superior product."<br /><br />Honda makes good stuff, but "superior" is your opinion. I own several Yamaha 9.9 4-strokes that I wouldn't trade for a Honda if you paid me. I swear these little Yamaha's are made by a Swiss watch maker.<br /><br />Some points of interest between the Honda 9.9 4-stroke and the Yamaha 9.9 4-stroke:<br /><br />The Honda uses a 222 cc block, the same as the smaller 8 hp.<br />The Yamaha uses a 232 cc block, unique to itself.<br /><br />Honda only adds a 4-blade prop to their 9.9 to get their 9.9 "Power Thrust" model.<br />Yamaha uses a different gear ratio, operating rpm, and a dual thrust prop for their "High Thrust" model.<br /><br />The Honda is more expensive.
