gearhead80 wrote:Apparently some on here have never really been around 4-wheelers or really seen what they are capable of.
And apparently you have never been around propeller driven marine engines and know what they are capable of.
gearhead80 wrote: The trans will more than handle what's going to be on the other end of the shaft. Think about the rolling resistance in the tires and the wieght of a quad vs turning that prop in water or mud. Think about the shock that is transmitted through the trans of on of these things while just riding it. The abuse it's designed to handle in rough terrain while on the throttle far more than most will ever pit it through.
Slow down cowboy, before you get your panties in a twist, you need to realize that the conditions an outboard or mud motor are subjected to are nothing like conditions faced on land. People have raised questions about the theoretical limitations of the system. On a 4 wheeler, there are more places for the shock loads to be absorbed between the ground and the trans output shaft...sidewalls of the tires, gear lash, even the suspension will eat some of the torque loads imposed on the trans. These are not there on a mud motor. It is a direct connection from the prop to the transmission
gearhead80 wrote:People need to get rid of the idea that lawn mover engines are the best for mud motor applications. News flash people, they work ok, the main reason they are used is because of the simplicity, cost and ease to obtain for manufacturing. Why do think there are guys modding the piss out of them? Cuz they are TURDS!!! Yes they will get you places an outboard can't go.
People use lawn mower engines because they provide ample torque while still small and light enough package to put it on the transom of a boat and not sink it. A boat will have to displace a certain amount to float a heavy motor/trans combo. The heavier the load, the more will have to be displaced. More displacement=more wetted surface. More wetted surface=more drag to overcome.
gearhead80 wrote:Yes in this project he will prolly find one or 2 gears that work best for prop size/pitch. But it will work as long as he is not trying to run it on a 20' boat. Gear reduction it a wonderful thing when it comes to torque multiplication.
Propping a motor is unlike anything else in the automotive/mechanical field. The whole process is completely subjective with too many variables to have a set in stone formula, but it comes down to this. A prop will run most efficiently at a certain rpm. Go above that rpm and you cavitate, go below that and you aren't running efficiently. (Efficiency is not
the same as his fuel burn rate) Most mud motors run in a lower rpm than outboards. This lower rpm, but higher torque allows them to spin props with completely different geometries. I say all of that to say this, if he tries to find a gear to run it in, hes going to fail sorely. Instead, he needs to find an rpm to prop to, and hope that the transmission is geared close enough that he can keep it close to that sweet spot while he quickly shifts. (Personally speaking, mud motors are a handfull as they are, add in changing gears...no thanks.) Once he comes off the clutch on a shift, there will be a massive torque load applied back to the prop..see the first quote reply...
If he decides to pick only one gear to run it in, what has he gained over running a transmission-less motor?
gearhead80 wrote:Good points here.. Plus if he does decide to shift the prop isn't going to stop spinning. Does the quad have to stop each time you shift? NO!!
The physics are apples to oranges here. When the clutch is engaged on a 4 wheeler, the forward momentum of the driveline allows for less of a shock to the system when the clutch is released. When the clutch is engaged in the water, there will be nothing keeping the prop spinning, so unless he is lighting quick, it will stop. Watch an outboard prop when the rpm is dropped from WOT to neutral; it stops almost immediately. There is no park on an outboard. There is F, N, and R, so if the prop isnt turning it is in neutral. Look how quickly the prop stops at :27.