dyno instead of test wheel

[blgrams]

how do you determine how much resistance to set when using a dyno to set timing at WOT?<br /><br />how do you determine how much to cut down a prop to make a test wheel?

 

[JB]

Re: dyno instead of test wheel

You read the Operator's Manual for the make and model Dyno you are using.<br /><br />A correct test wheel will offer the same torque load as a correct prop. Cutting down a prop wont cut it.<br /><br />Moving to General Outboard (non-repair topics)

 

[ledgefinder]

Re: dyno instead of test wheel

Actually, a cut-down prop will work OK. You just need to know how much to cut it. <br /><br />The main benefit of a real test prop is that it won't convert horsepower into thrust as efficiently, so the water in the tank won't get thrown around as much. A test prop is purposefully designed to generate as much resistance as possible, while generating as little thrust as possible. Of course, also, you know exactly what rpm your motor ought to run at/exceed with a test prop.<br /><br />Merc have a service bulletin a while back describing how much to cut down props for various motors. Cut each blade exactly the same shape so the prop stays in hydrodynamic (and static) balance. I don't know how much to cut them down for OMCs, but I plan to try this at some point, and will post the results. I have a 85/100hp test prop for the V4s, so I'll correlate to that with a common 17" V4 prop.<br /><br />"Have tools" if you get this done first, please let us know how much to cut. Test props are great diagnostic tools. You just back the boat into the water & have at it. Make sure you strap the boat down well first...

 

[blgrams]

Re: dyno instead of test wheel

I know that the test wheel is designed to put a specific amount of load on the shaft of a specific group of motors, I was wondering how that would be figured with a dyno. is there a chart in the owners manual which tells the opperator how much load to place on a specific model of motor? I assume too much and the motor will appear not to meet rpm's and too little and it will over rev. Is it by HP and if so what about the old motors that were measured at the motor not the shaft?<br /><br />just trying to understand it all.

 

[P.V.]

Re: dyno instead of test wheel

Marine dynos require you to "load" the engine, run it up to a specific WOT rpm, and read a specific psi reading per the dynos operating manual. If you don't have the "correct" readings, troubleshoot the fuel, ignition and/or mechanicals to find out why! I used to use a dyno about two or three times a day, five days a week at a previous employer.Too far from the water to always go! We never put much creadence in the 'readings" because if the "specs" where "off", yet the motor ran with no concerns, then just what were we gunna "fix"??? Loading the engine allow'd us to shoot fuel down the venturies, shoot timing, pull plug wires (balance test), etc... Since I'm now on the lake, we lake test just about everything! Cut down props can get expensive and where do you put all of 'em??? The only way you can tell a customer his boat runs correctly on the water is to....... Put it on the water!!! With his prop!