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Author Topic: Torque converter  (Read 97 times)

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Offline Mokai Dreamin'

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Torque converter
« on: July 28, 2019, 04:07:10 AM »
Was just pondering an idea today, and this one's a bit beyond my understanding so maybe somebody could shed some light on how this works.

I was thinking about the new design in the version 2.0 ES-kape, and how the engine is now rotated 90 and the extra room this provides. It would now be possible to install something like a torque converter for example. Mokai has an overdrive hooked up at the moment with this arrangement, but it's pretty much maxed out for performance from my understanding.

I talked briefly to Tom and to Rick at Mokai about this. My thinking originally was why not just go to a different gear ratio to spin the impeller faster, and was told that the engine really doesn't have enough  torque for this to happen. We are already starting out in essentially 3 gear with a 1:1 system. The Kohler has some extra torque so it could start out in say 4th gear, but beyond that it doesn't have the torque, and it simply works harder, but doesn't develop full speed. Not enough muscle at a given rpm.  In fact my understanding was if you overtax it, you actually reduce speed, so becomes counterproductive.

So my question is if you're starting out in third gear right now, what happens if you put something like a torque converter on the engine and allow it to start in first gear, and move up slowly to 4th gear. Less torque required right? Would  it be able to achieve higher rpm's at the impeller or would it  still be faced with the same scenario of running out of adequate torque to spin the impeller at faster speeds at a certain point/gear ratio?  What would be the limiting factor at this point? I can't  wrap my brain around this. HP or torque or both?

I've read the way that go-cart engines achieve the high speed is through a gearing system or transmission that allow them to achieve  higher speed slowly, which lessen the torque requirement. I know some of those have torque converters. So, just wondering if something like that would work on a Mokai with the newer 2.0 design? If you reduce the torque required to get up to max rpm, Could you actually go with something like a racing engine with torque converter in the ES-Kape 2? I know some of those are capable of 5000 and 6000 RPM, but just don't have the torque to work in a 1:1 system.  If you work up to 5000 rpm slowly, could you do it?
Crazy ideal or possible? If it is possible, I assume there's no free lunch, and perhaps the engine would just develop too much heat? What are other considerations? What about weight? Are these small engines that are designed for really high rpm's and HP much heavier? What does a torque converter weigh? Other considerations?
Best,
Troy

Offline Painlesstom

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Re: Torque converter
« Reply #1 on: July 28, 2019, 08:13:11 AM »
That only helps if you have wheels on the ground, the torque converter would effective give a lower "gear ratio" at the start to help get the wheels moving.. Don't have that scenario with the Mokai, the impeller goes to full speed instantly. The engine can't spin the pump any faster than is currently does, the only way to achieve more rpm is with more power at the engine.
Tom

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Offline happul3

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Re: Torque converter
« Reply #2 on: July 28, 2019, 10:10:04 AM »
  What would be the limiting factor at this point? I can't  wrap my brain around this. HP or torque or both?

Thing to remember is that HP and torque aren't independent characteristics. Torque (lb.in) = 63,025 x Power (HP) / Speed (RPM)
So it is not possible to be limited by one and not another at any given time. Also, high torque-low rpm motor will show exactly the same performance as low torque-high rpm one with the same actual HP when used with appropriate gearing.

As for the torque converter, to add to Tom's explanation, it is acting exactly like a variable ratio gearing (or CVT) during acceleration. At a constant speed a torque converter does do nothing except steal some of your motor power and convert it into heat. Since Mokai operates primarily at constant speed the torque converter does not seem useful at all.

Offline Mokai Dreamin'

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Re: Torque converter
« Reply #3 on: July 28, 2019, 10:41:49 AM »
Many thanks for helping me to understand how this works. I was just exploring possibilities with the latest design of the 2.0 that may help to improve speed. It seemed like at first glance there is more opportunity here for gains, but the deeper I dig, the more I'm coming to realize that any gains that could be had, are largely offset by weight of the engine or inefficiency of a gear system.

The other thing I'm seeing about a Mokai is once you start getting close to 200 pounds, you can't get the boat up on plane easily. Weight distribution becomes huge. Without moving my gas tank all the way to the front of the boat, the stern of the boat simply shovels into the water, and instead of going faster with more throttle, you go slower. Very counterproductive.

Increase buoyancy  too much to prevent the boat from digging into the water, and you end up with problems like the Stik boat has. Namely, cavitation. The boat doesn't sink deep enough into the water, and sucks up air every time you hit a small wave or bump in the water. When you start experiencing these various problems, you get a much greater appreciation for how hard it is to design an efficient small jet boat. Haven't heard from anybody that's over 250 pounds who has purchased one of the Stik boats, but I bet they experience less cavitation.

Anyway, appreciate the feedback!
Best,
Troy

Offline happul3

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Re: Torque converter
« Reply #4 on: July 28, 2019, 01:04:48 PM »
I was just exploring possibilities with the latest design of the 2.0 that may help to improve speed. It seemed like at first glance there is more opportunity here for gains, but the deeper I dig, the more I'm coming to realize that any gains that could be had, are largely offset by weight of the engine or inefficiency of a gear system.

I think you have already made quite a bit of progress with getting the most out of v2. It was very interesting to read about substantial improvements due to weight redistribution. Maybe you can also get a little more power from the motor too? Aside from modifying it, which is something I know much less than the real specialists in this forum,  you might gain something from changing the ratio. Basically, you'd want to operate motor at highest safe RPMs because that can produce maximum power. So if stock setup is 3650 rpm motor / 4380 rpm pump, reducing ratio to say 1:1.1 will give you 3981 rpm / 4380 rpm *if* one assume (incorrectly) the HP remains the same. In reality though the HPs do not stay the same but should go up and so the pump RPM will increase too above stock. That's admittedly a very simplistic view, but possibly useful. One related question is a degree to which you are limited by water intake. If you have access to clean, deep water you may want to try running with and without grate.