T or F: Crank weight affects torque?
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Kevin Cameron covered this as it applies to motorcycles, a heavy crank and flywheel will cover up for a poorly designed ignition system. If your spark is off at low rpms your torque is poor. Thats why crank triggers are popular now.
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Guys, guys - ROTATIONAL kinetic energy:
KE=(1/2)I(w^2)
Where w = velocity/radius
&
and if we consider a solid cylinder like a flywheel, I (the moment of inertia), is = (1/2)(mass)(radius^2).
"centrifugal force" is the inerital opposite and of equal magnitude of centripital force.
KE=(1/2)I(w^2)
Where w = velocity/radius
&
and if we consider a solid cylinder like a flywheel, I (the moment of inertia), is = (1/2)(mass)(radius^2).
"centrifugal force" is the inerital opposite and of equal magnitude of centripital force.
No need to be humble. From one Idahoan to another, I felt it was my responsibility to point out the computational error so that you don't underestimate the size rifle you will need for this spring's bear hunt...Lazy JW":36jrafo2 said:
Something like that... I find Ke (rotational and otherwise) to be a somewhat mythical figure of rather limited usefulness. I am more concerned about how heavy something is and how fast it is moving toward me (Mo=m*v). I much prefer my shrapnel to be of the heavy and slow variety; gives me an increased opportunity of seeing it coming and getting out of the way... 8)addo":36jrafo2 said:
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I have no clue as to what all the mathematics means 
But I'm assuming (what your saying) is that it is better to lighten the load by reducing the weight of;
Wheel/tire combos
Brake drums
Driveshafts
Torque convertors/Flywheels
Timing chain & gears
Valve train components
Or am I wrong???
Besides adding as much hp as I can to my car, I've also been removing anything that isnt critical to lighten it up as much as possible. I weigh everything I remove and you would be surprised as to how quickly it adds up!
Later,
Doug
But I'm assuming (what your saying) is that it is better to lighten the load by reducing the weight of;
Wheel/tire combos
Brake drums
Driveshafts
Torque convertors/Flywheels
Timing chain & gears
Valve train components
Or am I wrong???
Besides adding as much hp as I can to my car, I've also been removing anything that isnt critical to lighten it up as much as possible. I weigh everything I remove and you would be surprised as to how quickly it adds up!
Later,
Doug
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Anonymous
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The extra weight DOES give more torque but only in de-acceration due to its added inertia (does not slow as readily).
In other words it has almost no practical benefit for serious street applications where the engine itself has sufficient HP power to overcome hills without de-accelating (this is almost always). Even with less power if it did slow (like Datsun 1200) it would still need to be considered alongside the benefits of lightening.
Extra recripricating weight is good for trucks tractors and bulldozers or maybe if you want to hold 200 mph into a headwind (but it wont help you get to 200 faster)
Generally its a good idea to lose a bit of weight from the drivetrain. The safest place to do this is thought to be the flywheel. Although I have heard some engines rely on this weight to help balance out vibrations similar to the dampener on the front of the engine (anyone else?).
I would seek lots of advice first before I lightened even this.
I am certain that the extra weight does give more torque under power as the engine is slowing but I am still not certain if it does this at a constant speed with the same HP fed into it (are dyno readings ever done at constant speed?). (so my 200mph example may not hold up) Cant get my mind round this yet?
Could some of you knowlegable folks explain some of your tech talk a little more because some of us who are new to this are interested in this type of discussion as well?
Cheers Tim
In other words it has almost no practical benefit for serious street applications where the engine itself has sufficient HP power to overcome hills without de-accelating (this is almost always). Even with less power if it did slow (like Datsun 1200) it would still need to be considered alongside the benefits of lightening.
Extra recripricating weight is good for trucks tractors and bulldozers or maybe if you want to hold 200 mph into a headwind (but it wont help you get to 200 faster)
Generally its a good idea to lose a bit of weight from the drivetrain. The safest place to do this is thought to be the flywheel. Although I have heard some engines rely on this weight to help balance out vibrations similar to the dampener on the front of the engine (anyone else?).
I would seek lots of advice first before I lightened even this.
I am certain that the extra weight does give more torque under power as the engine is slowing but I am still not certain if it does this at a constant speed with the same HP fed into it (are dyno readings ever done at constant speed?). (so my 200mph example may not hold up) Cant get my mind round this yet?
Could some of you knowlegable folks explain some of your tech talk a little more because some of us who are new to this are interested in this type of discussion as well?
Cheers Tim
My .02. Does rotating weight increase torque? yes and no. No, it does not create more power. That is all done in the engine. Yes, it stores rotational inertia so that it can be used later.
Probably a more appropriate analogy for a flywheel (or any rotating mass) is to think of it as a rechargeable battery. It doesn't create power, it only stores it for future release. You have to insert energy in order to retrieve it later.
A massive battery would take a lot of charging to get to a certain electrical potential. Same with a large flywheel. You will have to absorb a lot of energy to spin it up. Once spun up, it releases that energy back into the system. This helps smooth out the rotation between firing strokes, helps maintain energy when engaging a clutch, smoothing out the engine on overrun with the throttle off.
A light flywheel will "charge" faster, absorbing less energy. But it has less to release. That makes throttle response better, but in turn could make shifting balkier and clutch action more sensitive.
Probably a more appropriate analogy for a flywheel (or any rotating mass) is to think of it as a rechargeable battery. It doesn't create power, it only stores it for future release. You have to insert energy in order to retrieve it later.
A massive battery would take a lot of charging to get to a certain electrical potential. Same with a large flywheel. You will have to absorb a lot of energy to spin it up. Once spun up, it releases that energy back into the system. This helps smooth out the rotation between firing strokes, helps maintain energy when engaging a clutch, smoothing out the engine on overrun with the throttle off.
A light flywheel will "charge" faster, absorbing less energy. But it has less to release. That makes throttle response better, but in turn could make shifting balkier and clutch action more sensitive.
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ouch, my head hurts 
A good example of a flywheel being used is in large bandmills. At one sawmill where I used to work, we had a set of band mills on a primary log breakdown that was underpowered. This was a quad (four bandmills) with 5' diameter wheels and 100 hp electric motors. We had increased the strain on the saws and increased rpms and feed speeds to the point that the motors were overloading. We located a set of wheels (used) that weighed almost twice as much as the original set. The only problem was we knew we couldn't start the new wheels with the old style motor starters, so we installed a set of electronic "soft starters". It took about three minutes to bring the mills up to speed, but once they were revved up the flywheel effect helped carry the load through each log and the motors didn't have to pull as hard in the cut, and were able to maintain the speed without overheating. We put an average of six logs per minute through this machine. The average load was actually higher, but the peak current draw was lower. In an internal combustion engine, the flywheel only has to carry the engine through to the next power pulse. And it is impractical to use a big enough flywheel to pull your truck up the next hill.
Joe
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It makes sense (according to buddy Newton) to consider the rotational momentum not at stored PE, but rather something in motion that stays in motion - hence the greater the weight (or velocity), the greater the momentum, the greater the force required to change it's course - to slow it down or speed it up (acceleration of deceleration).
My answer to the question would be: any weight added to the elements that rotate aids carrying the torque between power strokes. The disadvantage (covered already) is that power that could be transmitted to the wheels is absorbed into getting the greater mass to turn. The throttle response is delayed.
My answer to the question would be: any weight added to the elements that rotate aids carrying the torque between power strokes. The disadvantage (covered already) is that power that could be transmitted to the wheels is absorbed into getting the greater mass to turn. The throttle response is delayed.
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