durbans RPM & Flywheel theory

[durban]

. a heavy flywheel will keep the crankshaft spinning longer than a lighter the flywheel . when you let off the throttle & hit it again , there will be less " lag" between the time that the motor hits its power band or peak horse power RPM & the rpm it was spinning before you let off the throttle

the down side from a heavy flywheel is that from a low rpm to a high rpm will take longer . so the lighter the flywheel the quicker the rpm .its got to do some thing with wieght & mass

when i changed flywheels i noticed the difference ,

 

[DargelJohn]

Re: durbans RPM & Flywheel theory

. a heavy flywheel will keep the crankshaft spinning longer than a lighter the flywheel . when you let off the throttle & hit it again , there will be less " lag" between the time that the motor hits its power band or peak horse power RPM & the rpm it was spinning before you let off the throttle

the down side from a heavy flywheel is that from a low rpm to a high rpm will take longer . so the lighter the flywheel the quicker the rpm .its got to do some thing with wieght & mass

when i changed flywheels i noticed the difference ,

Ok, And the heavier the flywheel, greater is the torsional force being applied to the flywheel key and crankshaft.
Possible failure?

 

[durban]

Re: durbans RPM & Flywheel theory

Ok, And the heavier the flywheel, greater is the torsional force being applied to the flywheel key and crankshaft.
Possible failure?

this probably explains why some blokes have sheared or damaged key ways aye m8t . iam gonna study my fly wheel & see where i can machine it to make it lighter & then increase the prop size .

 

[Dabbler_E]

Re: durbans RPM & Flywheel theory

. a heavy flywheel will keep the crankshaft spinning longer than a lighter the flywheel . when you let off the throttle & hit it again , there will be less " lag" between the time that the motor hits its power band or peak horse power RPM & the rpm it was spinning before you let off the throttle

the down side from a heavy flywheel is that from a low rpm to a high rpm will take longer . so the lighter the flywheel the quicker the rpm .its got to do some thing with wieght & mass

when i changed flywheels i noticed the difference ,

The "theory" is simply a restatement of the law of inertia. The response of the motor to throttle probably makes sense if it is in neutral, but there is so much water resistance encountered by the propeller in the water that the inertia of the flywheel is probably a negligible component of the forces counteracting the force of the motor. And, as DargelJohn indicates, the components of the engine are designed for a particular weight flywheel. Why court disaster just to modify how quickly a motor in neutral responds to throttle?

 

[jbjennings]

Re: durbans RPM & Flywheel theory

Durban,
I'd think that the factory would have made the flywheel as light as they could to cut down on aluminum costs to start off with. I'd leave the flywheel alone. As mentioned, that thing is spinning pretty darned fast and you don't want it shattering and sending pieces flying at you. THose engineers are educated for a reason!
JMO,
JBJ

 

[WernerF]

Re: durbans RPM & Flywheel theory

The flywheel's outer mass counts much more to inertia than the inner mass (square of radius). Thus most of the mass is located there.
I wouldn't alter the flywheel inertia. You may hit a crankshaft resonance. How do you want to measure and maintain dynamic balance? With lower inertia you may overstress the driveshaft or gears with increased torsion oscillations. Because there is less energy in the flywheel to overcome cylinder compression you may have to increase idle rpm thus wearing the clutch dog.
Higher inertia is able to apply more force to the crankshaft/driveshaft/gears/prop in case the prop is hitting an object or winding a rope.

 

[nwcove]

Re: durbans RPM & Flywheel theory

Durban,
I'd think that the factory would have made the flywheel as light as they could to cut down on aluminum costs to start off with. I'd leave the flywheel alone. As mentioned, that thing is spinning pretty darned fast and you don't want it shattering and sending pieces flying at you. THose engineers are educated for a reason!
JMO,
JBJ

+1 on that!!! have you ever seen the results of a clutch/pressure plate exploding in a high performance car?? my buddy Joe has....we now call him " no toe Joe", and he was very lucky!! dont mess with the flywheel.....they are engineered for your safety!

 

[V153]

Re: durbans RPM & Flywheel theory

A lighter flywheel is said to get you out of the hole and/or to max rpm faster. But whether it improves top end is arguable.

Fwiw I have a couple spares & plan to lighten one of em up a lil bit and see for myself what happens. Only way to know for sure.

I think it's important to note motors are built 'one size fits all'. If'n ya got a tugboat you might need a heavier flywheel, got a lil go fast boat ya might not?

Will advise.

 

[durban]

Re: durbans RPM & Flywheel theory

put it this way , you can start your car without a fly wheel , by push starting it , ive never heard of a outboard motor being tow started with another boat towing it , the only reason why i think they put it on was in the early days for something to generate electricity & some where you could attach a rope to ,turn to start the motion of electrical generation , my theory some how does make some sense . because speedy way racers do it on their cars , that's why they achieve such great speeds together with what else they modify , so why not try , ive started , this has never been experimented i could be wrong ,i suppose we take things for granted what others tell us we should use , one person made a flywheel & every one uses what is provided , nothing stops us to try another one it may work ,

 

[durban]

Re: durbans RPM & Flywheel theory

+1 on that!!! have you ever seen the results of a clutch/pressure plate exploding in a high performance car?? my buddy Joe has....we now call him " no toe Joe", and he was very lucky!! dont mess with the flywheel.....they are engineered for your safety!

if i modify , i already thought about the safety side of things , i would get stainless netting wire and epoxy it into my cowling cover any thing that comes off not gona go through the netting .

 

[1946Zephyr]

Re: durbans RPM & Flywheel theory

Interesting topic. Compare a 1956 Mercury Mark 30, to a 1956 Evinrude Big Twin. A huge diggerence in how they accelerate. If a guy was to modify a flywheel to lighten it up, you could possibly do so, by shaving it down to where the outer diameter is about 1/2 out from the magnets. It will have to be a manual start though, because the flywheel ring gear won't be present.

 

[Mas]

Re: durbans RPM & Flywheel theory

There you go Zeph...just compare a motor with the ring gear and then with the ring gear removed...just rope start the latter. That should be enough reduced mass to effectively (and safely) compare results.

Mas

 

[tx1961whaler]

Re: durbans RPM & Flywheel theory

put it this way , you can start your car without a fly wheel , by push starting it , ive never heard of a outboard motor being tow started with another boat towing it , the only reason why i think they put it on was in the early days for something to generate electricity & some where you could attach a rope to ,turn to start the motion of electrical generation , my theory some how does make some sense . because speedy way racers do it on their cars , that's why they achieve such great speeds together with what else they modify , so why not try , ive started , this has never been experimented i could be wrong ,i suppose we take things for granted what others tell us we should use , one person made a flywheel & every one uses what is provided , nothing stops us to try another one it may work ,

This has been experimented on many times, and push starting a car has nothing to do with a flywheel. Do your experimenting and have fun, but first research why the flywheel is on there to begin with. Hint: is has nothing to do with electricity or starting the motor. Also calculate the kinetic energy of a 2 kilo piece of flywheel separating from a 30cm disc rotating at 5000 rpm.

 

[schematic]

Re: durbans RPM & Flywheel theory

Please explain how to "push start" a car without a flywheel.

 

[bob johnson]

Re: durbans RPM & Flywheel theory

Durban,
I'd think that the factory would have made the flywheel as light as they could to cut down on aluminum costs to start off with. I'd leave the flywheel alone. As mentioned, that thing is spinning pretty darned fast and you don't want it shattering and sending pieces flying at you. THose engineers are educated for a reason!
JMO,
JBJ

you think flywheels are made of aluminum?

if Durban does start cutting into his flywheel , I certainly hope he balances it with precision before he reinstalls it.

bob

 

[RogersJetboat454]

Re: durbans RPM & Flywheel theory

the only reason why i think they put it on was in the early days for something to generate electricity & some where you could attach a rope to ,turn to start the motion of electrical generation

Think about this critically...
If a flywheel was such an unnecessary piece of equipment, why are they still using them on brand new outboards?

Have you ever tried to start a lawn mower with out a blade on the engine? There is a reason why so many who try report a wrist snapping experiance when the engine kicks back. The simple truth is that the aluminum flywheel found on most lawn mowers does not have enough mass/inertia to maintain the engine spinning in the desired direction. Once the engine comes up on compression stroke, since the fuel is usually lit off before TDC, the piston gets forced back wards (spinning the crank in the opposite direction) since the crank did not have enough umph behind it to push the piston through TDC and allow the force of the combustion to spin the crank in the right direction. With a blade on, the engine has enough inertia to get through TDC.

Your outboard is no exception. Some meat may be able to be removed from the flywheel with no ill effect, but its a balancing act. And speaking of balance, if your balance is off at 5K RPM or better, wire epoxied to the lid of the engine isn't going to stop a shattered flywheel from exiting the fiberglass engine cover.

You should see what a flywheel can do to a piece of 1/4 inch or better steel used for a bell housing. It's a pretty sobering sight.

 

[jbjennings]

Re: durbans RPM & Flywheel theory

you think flywheels are made of aluminum?

if Durban does start cutting into his flywheel , I certainly hope he balances it with precision before he reinstalls it.

bob

I've never picked up a flywheel...... They're not aluminum???

 

[Chinewalker]

Re: durbans RPM & Flywheel theory

Interesting topic. Compare a 1956 Mercury Mark 30, to a 1956 Evinrude Big Twin. A huge diggerence in how they accelerate. If a guy was to modify a flywheel to lighten it up, you could possibly do so, by shaving it down to where the outer diameter is about 1/2 out from the magnets. It will have to be a manual start though, because the flywheel ring gear won't be present.

To take the Mark 30 analogy a bit further, the racing version, the Mark 30H, has a flywheel that's not much more than a sheave to catch the recoil cogs. Everything beyond the sheave is gone. This helps with acceleration out of the corners.

Further, although a motor may run with a lighter flywheel, that inertia that comes with the extra mass helps with smooth shifting, keeping the motor from stalling when you put it into gear. The motor can maintain the lower RPM and transition from no load to loaded without stalling. Also, clutch dogs last longer when the motor is shifted at low RPM.

Going back to the Mark 30/30H models, the racing version has no clutch to worry about. BUT, a well tuned one may need help starting by having the prop lifted out of the water to reduce the load. Once RPM are up, the boat is dropped in and away you go...

 

[durban]

Re: durbans RPM & Flywheel theory

Please explain how to "push start" a car without a flywheel.

i was not thinking properly on this one you one up on me ok , it needs the ring gear & the flywheel is all part of it

 

[durban]

Re: durbans RPM & Flywheel theory

2 simplify things should we rather say different weights in flywheels for different size props , maybe we will get better performance this way ,