Going back to the original question regarding the 348 flywheel specifically. I think there might still be a question of whether the original Voith flywheel and all its' associated quirks are important to long-term reliability. The engine doesn't employ a traditional harmonic damper, what happens if it is replaced with a slab of iron or aluminum? In my experience a significantly lightened flywheel will "get old fast" in a street-driven car. Unless you really want a jerky ride.
Three laws of thermodynamics: 1: You can't win 2: You can't break even 3: You can't get out of the game But back to the Flywheel. An engine produces TQ and HP. After the RPMs of the engine are adjusted through the gear box, and differential, this rotational TQ is applied ot the Rear wheels. At this point, the weight of the car plus the weight of the rotating masses are inertial forces holding back the acceleration. The weight of the car is a linear inertial mass, the rotating components have what is known as the first moment of inertia. Given an axis of rotation, the farther the weight is from that axis, the more it contributes to the inertia. Thus, rotating inerita is the integral of weight times distance from axis. Thus, given two shafts of the same weight, the one with the larger diameter has the greater first moment of inertia. Parts of the rotating chain: Engine crankshaft, Flywheel, Clutch+Disk, Drive shafts, Wheels, tires, brake rotors. There is little on can do to the rotational inertia of the crankshaft, the flat-plane crank is just about as light as one can be made. Same with the transmission shafts and gears and the drive shafts. The wheels are admirably light already. The weights of the tires are more or less constant across manufactures at a given size. Brake rotors are more likely to grow in inertia than loose inertia (rotating mass). So about the only component one has access to to lighten the rotating inertia is the flywheel. Flywheels are both heavy and a good deal of the weight is distributed far from teh axis of rotation, making it have considerable inertia. One can remove weight from the outside flywheel and have a greater effect to the performance of the vehicle than taking the same amount of weight off the center of the FW. With rotating thingies, its where you remove the weight not how much you remove. The lighter the car, or the lighter the rotating masses or both, the faster the acceleration. The faster the acceleration the greater the performance--even if the HP and TQ did not change! Lightening the flywheel does not change the engine output, it does change how the engine output accelerates the vehicle.
Manny, LOL,, ok yes I am talking about HP, but not Steady State,, instantaneous. (please don't make up your own thermodynamic properties.) When you integrate HP with time what do you get...? What kind of engineering, is your MS in...? Cheers I love a good debate. Edwardo Mechanical Designer Multiple Mechanical and Electronic Patent Holder. below Average genius.
A+ Yes, yes and yes. if you were my student when I was teaching Nuclear Physics and Nuclear Chemistry, For 3 years, For the Department of Defense. You would get a free GeDunk. Edwardo
Same experience here. I had the flywheel significantly lightened on one of my cars in 1982. Still own it, still drive it. Can be fun and can be annoying. Used to be a daily driver. Not any more. It's a compromise, not a simple matter of "Lighter is better."
LOL and no, I won't have to sell my Ferrari to pay tuition. (To get into A Real University,, it doesn't take money, it takes grades.) Unlike those Private Schools, you don't get daddy to bone up on a tutor, or donate funds to keep you in. If you fail in Engineering @ Cal Poly, your gone...! ( I see you need to subscribe, do need me to loan you $15.00...?) Sorry I am not out for hire now, but thanks for the offer. Edwardo World leading Nuclear, Chemical, Mechanical Design and now,,, Agriculture Engineer.. I thought I was wrong once, but, I was wrong. Image Unavailable, Please Login
Oh....this is no good. There is nearly no energy loss associated with the flywheel and what is lost has nothing to do with the weight. The energy lost due to the flywheel is from friction/drag in the air, which is a function of the physical dimensions and nothing else. Driveline losses are all friction related (gear on gear, gear in oil, ect) and the losses due to the flywheel are negligible in comparison to the gears. As others have already pointed out, alterations to the flywheel do not affect hp or tq, but will affect drivability and acceleration rate which are related to the energy stored in the flywheel, not energy consumed by the flywheel.
Drive train components eat HP through friction loss, a flywheel has no friction loss, you will use more energy accelerating a heavy flywheel than a light flywheel so during acceleration more power to wheels but no more power made by the engine, under constant speed power to the wheels will be the same whether you use a 100lb flywheel or no flywheel at all. Drivability is another matter and the stored energy in the flywheel helps. Russell
You missed my point. I am talking about horsepower delivered to the wheels while accelerating. You are discussing two observations re. a flywheel - its intended purpose of smoothing out torque and the energy that is transferred while the clutch is being engaged, that I was not. I was not addressing how removing mass from a flywheel affects either of the above observations, but how it affects HP at the wheel, while driving down the road and accelerating or as measured by a dynamometer while the engine is accelerating. A dynamometer does not measure a flywheel's ability to smooth out discrete pulses of torque resulting from individual cylinder explosions, nor does it measure HP while someone is engaging the clutch. Lightening a flywheel will increase vibration from the engine and provide disappointing acceleration during a “launch” - while the clutch is being engaged, becasue there is less energy stored in the flywheel. However, it will allow the car to accelerate faster after the clutch is engaged and that is what I was referring to. The mass of a flywheel has no effect on the amount of torque or horsepower an engine produces, but it does have an effect on how much of that horsepower gets delivered to the wheels while accelerating, which is what matters. HP is produced from torque. HP is the ability to deliver torque at a specified rpm. It is torque x angular velocity. Not true if you measure HP at the wheels, where it matters. Also, and you probably know this, but while I am being anal I have to say that flywheels store energy, not torque. Saying a flywheel stores torque is like saying a moving freight train stores acceleration. There is energy stored there, available to accelerate a mass. Not true if the clutch is engaged and you are accelerating the car. Again, I am referring to horsepower at the wheels while accelerating, which is what we all care about. Perhaps a good way to explain this is to imagine a 4000# flywheel as someone previously remarked. Let’s also imagine you have an imaginary indestructible clutch. If you depress the clutch pedal and rev the engine it will take a long time to rev the engine up. Once you are there, when you engage the clutch you are gonna be launched. Once you read a steady velocity and then step on the accelerator what do you think will happen? The engine will produce the same torque at the same rpm as before. In other words, it will produce the same horsepower as before. The problem is, now a disproportionate amount of that torque is going to accelerate the flywheel and not the wheels. The result is that the car will perform like a dog. If you put it on a dyno you will see a dramatic decrease in HP to the wheels, because there is a dramatic decrease in torque to the wheels. In summary, the mass of a flywheel has no effect on an engine's torque or horsepower. However, it does affect how much torque or horsepower is available at the wheels while accelerating, because some of the torque from the engine will be required to accelerate the flywheel. How much is required depends on the flywheel's mass. Note that I keep saying "while accelerating". Lightening a flywheel does not have a beneficial effect while traveling at constant speed. And if you are measuring HP at the rear wheels on a dyno while holding engine rpm constant and braking the rollers, you will not see an increase in HP at the wheels due to a lightened flywheel. That is because there is no torque being used to accelerate the flywheel. The purpose of the flywheel is to smooth out the roughness of the discrete pulses of torque coming from the engine. If you remove mass from a flywheel you decrease its effectiveness at doing this, but you will increase HP delivered to the wheels while accelerating.
Edwardo, Cal Poly, Los Osos, Defense Dept, Italian cars! I'm just trying to connect some dots... Do/Did you know Cal Eustaquio? Rick
I don't disagree with what you wrote but how does it relate to what I posted?? Quote: Originally Posted by eulk328 View Post source: http://www.rogueengineering.com/Merc...gory_Code=LTWF "Flywheels are a BIG deal The drivetrain is the key for marrying the power from the motor to the wheels. A key components in this transfer of power is the flywheel. Using an aluminum flywheel in place of the factory part (generally a heavier, dual-mass unit) can reap some benefits, but if improperly designed or manufactured, can produce detrimental results. It is no secret that an aluminum flywheel can weigh as little as 1/3 of the weight of a factory dual mass unit. Because the flywheel resides on the end of the engine crankshaft, a unit that is too light can cause premature synchromesh wear, excessive low end clutch chatter, or worse, possible engine damage. Excessively lightweight flywheels also lack initial inertia, causing the car to stall when the RPMs drop near idle. These are some of the reasons why Rogue Engineering's PCS does not strive for the ultimate lowest weight when it comes to the flywheel. For example, our E36 M3 flywheel replacement still weighs over 10 lbs. (compared to the factory 24 lbs.). "
+1 And, to make sure we are perfectly clear - as you state, the HP and TQ from the engine does not change, but the HP and TQ at the wheels, where it matters and where it is measured by a dyno, does. I think this is where some people get confused.
Including you Hp and Tq at the wheels measured on a dyno does not change when you change the flywheel unless you are using an acceleration type dyno because acceleration does change with flywheel weight and what you are seeing is really error due to your measurement method. A heavier flywheel stores more energy than a lighter one. This means more energy goes into accelerating it and making the car accelerate slower but it gives back more energy when you try to decelerate it smoothing out the pulses between pistons firing. The top speed for the car remains constant with flywheel changes because the hp and torque at the wheels remains constant, but the time to get there is reduced with a light flywheel .unless you bogged or stalled off the line because there wasnt enough stored energy to properly launch the car or broke your crankshaft or transmission due to the fatigue from the more intense power pulses moving through the drive train. A lot goes into matching the flywheel to the application, but it does not in anyway alter hp or tq measured anywhere.
I think what is getting confused, here, is the nïeve understanding of acceleration. We all know the old equation F=m*a. However, when there are rotating components involved in the process the equation (neglecting some multipicative constants) is F=(m+i)*a. That is, the rotating inertia gets added to the mass of the vehicle being accelerated. The rotating mass also changes as different gears are selected, so one reads different HP in different gears. This is due to the various parts rotating at different relative velocities as the gear ratios are changed. Rolling wheel dynomometers have an assumption as to how big this 'i' component is. Changing the 'i' in a vehicle, still does not change the TQ at the rear wheels (or HP), it changes the "effective" mass of the vehicle. So, changing the weight(inertia) of the FW and not telling the dyno about this change WILL show up as increased TQ and/or HP. That it shows up this way is due entirely to the misinformation fed the dyno (not changing the inertial assumption).
I'm not buying this. If a car’s mass is accelerating linearly, then its flywheel is accelerating angularly (as well as linearly, but that is beside the point). If the flywheel is accelerating angularly then some torque is required to do this. The amount of torque required to do this is dependent on the rotational inertia of the flywheel. If you remove mass you will lower its rotational inertia. Let’s try this. An accelerating engine outputs torque T at some rpm. At that instant an amount of torque equal to T1 is required to (angularly) accelerate the flywheel. This torque T1 is directly proportional to the rotational inertia of the flywheel. The torque available past the fly wheel is T-T1. Now, if the rotational inertia of the flywheel can be lowered then a lower amount of torque will be required to accelerate the modified flywheel an equal amount. Let’s call the torque required to do this, T2. Now the torque available past the flywheel is T-T2. Are you telling me (T-T1) = (T-T2) ? While the car is accelerating, (T-T2) > (T-T1). In other words, while the car is accelerating, all other things being equal, there is more torque put to the wheels when the flywheel has had mass removed. When the car is not accelerating T1=T2=0.
That's all about right, but what you are missing is that there is no time component in torque and no acceleration term in hp so they are constant time time and delta time respectively. As Mitch pointed out a couple times now, the F=ma equation is the right one, the F (torque is constant, it is the m erm you are messing with when you change the flywheel weight and it does affect a (acceleration)......but hp and torque don't change.
Of course not. Hp and torque remain the same. But they are spent in different places. That's why I gave the mental experiment at the very beginning of this thread. A 2 ton flywheel will sap lots of BTUs that will no longer be available at the rear wheels. A lighter flywheel will not sap so many BTUs, which means that more energy will be available at the rear wheels. It's an easy mental experiment.
eeeeehhhhh, sorta... you are on the right track, maybe just the wrong words.... SOONER torque? So no, there is not MORE torque. Whatever torque that is available is merely available SOONER as less is put into the inertia of the flywheel. The max torque of the motor (height of the line on the graph) is constant. The availability of the torque (area under the plot) is expanded. The plot line of the lightened flywheel will be more steep, however it will have the same max torque plot point as the heavy flywheel. The heavier flywheel just takes longer to get there. Hence the performance aspect of a lightened flywheel. You get to use that maximum output of the motor more quickly. Rick
Its an easy experiment that gives you an incorrect answer because its based on an incorrect assumption. A flywheel does not disparate energy, it stores it and will make the energy available for use under the correct conditions. The 348 we are discussing will almost certainly have a better 0-60 time and maybe a better 0-100 time with a stock flywheel than with a light flywheel because it will launch better/smoother as the flywheel release the energy its storing. The light flywheel car will probably do better 60-100 and will certainly do better 100- 140. The general rule is street cars want stock flywheels, track cars (road course) wants a light flywheel to perform best. Ferrari knows how to make light flywheels and light flywheels cost less to produce, but they install heavy flywheels on their street cars because the heavy flywheels make the car perform better on the street.
I dont want to give the impression that Im down on light flywheels, Im not and here are a couple pics of the flywheel/clutch set-up I build for my 308. Its 17.0 lbs with the clutch and ring gear making it almost exactly ½ the weight of stock and about ¼ the rotational inertia of stock. This set-up will be used on the street and I expect it to work quite well .with an engine that makes 450-500 ft-lbs of torque so it doesnt need or want any stored energy to launch properly. On an engine that made 300 ft-lbs of torque the stock flywheel/clutch was about perfect, at the stock 187 lb-lbs the stock flywheel/clutch was a bit too light and require the engine to be at about 5500 rpm to get a good launch which is pretty hard on the drivetrain. You need the right weight flywheel for the application. Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login
Everything has losses. From your motor at the crank to rear wheels is often a 17% loss. This is why a dyno shop will add 17% of the measured rear-wheel output on their dynometer to give you the displayed hp for your car. When you increase the mass of drivetrain components, you increase the losses. The mental experiment that I gave you, which you have yet to accurately perform, is to imagine your car with a two ton flywheel. How much performance did you get? Now reduce the weight of the flywheel, in your head, to 1 ton. Did performance improve or remain precisely the same? Now reduce the weight of the flywheel to 200 pounds. Did performance improve or remain precisely the same? Now reduce the weight of the flywheel to 20 pounds. Did performance improve or remain precisely the same? Now reduce the weight of the flywheel to 10 pounds. Did performance improve or remain precisely the same? Do you get better performance with a drivetrain that loses 20% of the motor's output, or with a drive-train that loses only 10%? Notice that the motor produces the same power in all instances.