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Light Flywheel= Loss Of Torque

Discussion in 'Engine Building' started by saturn_boy96, Mar 28, 2003.

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  1. saturn_boy96

    saturn_boy96 88 C1V1C 53D4N DR1V3R

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    In a previous post it was stated that a lighter flywheel can cause a loss of torque in low rpm and a gain of horse power in high rpm so i wanted to know how this occurs.
     
  2. lsvtec

    lsvtec GNU/Linux Evangelist

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    I may be over simplifing, but I don't think a lightened flywheel = loss of torque.

    Torque is simply force with a rotational component. For simplicity's sake let's ignore the rotational component for the moment. Force = Mass(M) * Acceleration(A). So if you decrease M and leave A constant then you would lose torque. But a lightened flywheel will accelerate faster than the stock unit so if you should see the same amount of torque maybe a little more.

    Where people are coming from when they say you lose torque with a lightened flywheel is a lightened flywheel has less momentum than the stock unit so it can "transfer" less torque to the drive train in the moment when the clutch engages the flywheel. So you have to give an engine with a lightened flywheel more gas to prevent it from bogging as you let the clutch out than you would an engine with a stock flywheel.

    Hope that helped some.
     
  3. micah

    micah Senior Member

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    and when your dumping the clutch and shifting at 8k rpm's you dont really have to worry about bogging down heh
     
  4. D See 2

    D See 2 Senior Member

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    so if the engine is turning less mass, wouldnt it give you better gas mileage? and for that matter wouldnt the lighter mass be easier on you tranny synchros?
     
  5. micah

    micah Senior Member

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    maybe slightly better gas mileage but then again your engine is revving much faster and using more fuel, same thing for tranny, might be easier fr it because its lighter, but your gonna be giving it more hell so it prolly all evens out in the wear and tear
     
  6. saturn_boy96

    saturn_boy96 88 C1V1C 53D4N DR1V3R

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  7. monzee

    monzee Member

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    recent mod up on my EK4.. from stock flywheel and 4.4 ITR ttanny to lighter flywheel from Toda and 4.785 CTR tranny
    Hell of a fast pickup accelaration but loss out on top end speed.. lower rev limits too..
    Higher compression from the pistons.. (so becareful not to over rev) :spin:
     
  8. saturn_boy96

    saturn_boy96 88 C1V1C 53D4N DR1V3R

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  9. K2e2vin

    K2e2vin Senior Member

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    when the engine starts turning faster, it needs more inertia to keep the engine stable. thats why many high rpm engines use harmonic balancers and counterweights on the cranks(when people lighten the cranks, they try to remove just a little bit of weight).

    about the engine reving much faster and using more fuel, thats not really true. in most cases you use more fuel when theres more power needed to move the vehicle.
     
  10. sportlinecrx

    sportlinecrx Banned

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    Here's the deal...

    the less torque is referring to when the car is cruising. the lighter mass needs more torque to keep it rotating steadily at faster speeds. its like a frisbee. a lightweight frisbee would need alot more power to keep sailing through the air like a normal wieght frisbee. the problem is not in the launch, its in trying to sustain momentum for a cruise, especially at higher rpms.

    the lightwieght flywheel will launch and accelerate faster, but needs a healthy diet of constant power and torque to keep it rotating at a steady rpm. thats where the loss in gas mileage comes into play. u got to keep your foot down on the gas because the lighter flywheel loses momentum very quickly.
     
  11. white_hot_wagon

    white_hot_wagon Member

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    so what kind of flywheel is gonna offer the best compromise? is there such a thing as a little heavier lightweight flywheel? all the ones i see are either about 8 lbs or 11 lbs
     
  12. geoff19crx

    geoff19crx Junior Member

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    if someone don't mind please explain the reasoning of this. as i and a lot of others understand it you only get an improvment. as i have always understood it an engine will use more gas under load. now a stock flywheel will weigh twice as much as an aftermarket one. with that in mind it will also require more energy to turn it. next maintaining speed should also pose no problem because again it would require less energy to turn the flywheel. the only negatives i have heard would harmonic vibration which can be cured having the bottom end balanced. a simple test, go into your front yard grab a peice of string and two different size rocks or whatever both of different weight. have the string about 8 to 9 ft long and try to twirl it above your head. everytime, it will require more energy to start and maintain motion for the heavier object. if anything a lightened flywheel actually increase power slightly and also makes your available hp more usable because it would require less energy to keep the wheels moving.
     
  13. phunky.buddha

    phunky.buddha Admin with a big stick Admin VIP

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    Ok, let's break it down to basics...

    Mass = Inertia

    Inertia = Resistance to motion change

    If you have more mass, you have more inertia... and therefore more resistance to change in motion. Objects with more inertia require more force to change their direction/speed/motion than objects of lower inertia.

    In the case of the heavy flywheel, that's more resistance to acceleration as well as deceleration. When your engine is spinning in neutral and you engage the clutch to start moving, the flywheel helps your engine overcome the added load of the car's mass... effectively, the inertia of the flywheel (spinning) helps to overcome the inertia of the car (sitting still, not wanting to move). If your flywheel weighs 20 pounds and your car weighs 2000 pounds, you can see that a 20 pound flywheel will help to move the car better than a 10 pound flywheel will. It resists the change in motion that the car is imparting upon it more than the lighter flywheel, so it will require less input from the engine, and start the car moving along a bit smoother.

    Analogy:

    Ever go bowling? Compare an 8 pound bowling ball to a 16 pound bowling ball. The 8 pounder is easier to accelerate (from the stopped position to you throwing the ball at higher speed) and easier to direct (aim). Your arm also gets less tired with the 8 pound ball. The drawback is that the ball loses more speed toward the end of the bowling lane, and may not knock down as many pins as you want. You also have to be more careful with controlling the direction of the ball, since it's easier to fling out the wrong way if your arm twitches or something The 16 pound bowling ball is harder to accelerate and harder to direct, but it carries more speed at the end of the bowling lane because of its higher mass (and resulting higher inertia). It knocks more pins down. It's also harder to send the ball careening into someone else's bowling lane, because it's harder for your arm to suddenly jerk it to the side.

    Now relate this analogy to a car... the pins at the end represent your car's weight/mass, the bowling ball is the flywheel, and your arm is the engine. The lighter flywheel will be easier to accelerate and decelerate- so you'll have quicker starts, faster acceleration because the flywheel has less inertia to overcome, and quicker shifts because the revs drop faster when you let off the throttle. The downside is that you have to control the flywheel more, since the direction (speed of rotation) varies that much more. This is why people say that an "8 pound flywheel isn't good for a daily driver". I don't have any problem driving with mine. The heavier flywheel has higher inertia than the lighter one, so it will start your car from a stop more easily (knock down more pins), but it will hurt you everywhere else. It takes more force/power to accelerate (overcoming more inertia), doesn't allow you to shift as quickly (revs don't drop fast enough), but it is easier to drive because the speed of rotation doesn't change as rapidly as the lighter flywheel. Small changes in your throttle position don't change the revs as much, because the power blips are just soaked up in the heavier flywheel. This is why people might think that "a lighter flywheel takes more gas while cruising", because that lighter flywheel takes more attention at the gas pedal than the heavier one to maintain speed. The lighter flywheel will give you better gas mileage.. ever push that 8 pound bowling ball on the ground at a constant speed? Now try the 16 pounder- which one takes more energy to push? The 16 pounder. It's the same as the flywheel.

    Do you lose torque with the lighter flywheel? Yes and no. You lose torque to start the car moving, since less energy is stored in the flywheel- so you have to apply more torque from the engine. On the other hand, you use less torque to overcome the inertia of the flywheel while accelerating and decelerating, so you can use the torque from your engine more effectively. You don't lose any torque when going to a lighter flywheel- you just change the source and application of torque in your car's drivetrain.

    So...

    Light flywheel: better acceleration, better mileage, takes more skill to drive
    Heavy flywheel: worse acceleration, lower mileage, takes less skill to drive

    It's that simple.

    :lol:
     
  14. saturn_boy96

    saturn_boy96 88 C1V1C 53D4N DR1V3R

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    now, thats how i always understood it, until a post a few weeks ago, but now its all cleared up thanks Calesta and everyone.
     
  15. phunky.buddha

    phunky.buddha Admin with a big stick Admin VIP

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    :lol:

    Just trying to help out... it looked to me like nobody was understanding the basics behind why we have flywheels attached to our engines in the first place. Once you know that, everything else related to them is easy.

    :lol:
     
  16. dohcvtec_accord

    dohcvtec_accord WRX Sellout

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  17. brc80

    brc80 Senior Member

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    So whats a good wieght, for a daily dirven car?
     
  18. dohcvtec_accord

    dohcvtec_accord WRX Sellout

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    I run an 8.5-lb flywheel without any problems. You'll take a few days to get used to it, then it'll be just like driving a stock flywheel. As Calesta said, it just takes a little more skill.

    Remember how hard it was to drive a stick when you were first learning? And see how easy it is now? Kinda the same principle. :)
     
  19. likaciv

    likaciv Member

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    Higher compression?? I have a feeling thats wrong, the reason you shit blew is because of valve float, not a flywheel, and if anything it will help top end. Less rotating mass. You engine reving faster just made the float all the more evident and eventually came to the point where it destroyed your head and piston. Not flaming but thats what im understanding from your post. BTW what else did you have on your motor to be able to produce power/shift at 9K??
     
  20. vroomvroomHB

    vroomvroomHB Member

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    so what kind of fly wheel would you recommend for my motor? im doin all motor ls/vtec
    money is no object.....to a certain point. =)
    thanx in advance
    -Omar
     
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