Aluminum Flywheel ???

I'm going to be installing one on my car, but there are a few things I'm wondering about. I've heard of bolts sinking into the aluminum, and the expansion/contraction from the heat causing the flywheel to become loose. Should I have a thin plate (something like a large steel washer with holes for the bolts drilled in it.) made for it to protect from this problem?

Also, how necessary is a scatter shield?

Why do you even want an aluminum flywheel. Do you own like a honda or something. hahah. Anyway a scatter shield helps keep you legs in tact. When you run high rpm and your fly wheel breakes it keeps pieces of metal from flying into your feet.

Do flywheels really break that often? Any idea where I could get a SS, or could someone just make it for me?
Thanks for the info

I would think that if you had a good steel washer under the head of each bolt and had the bolts torqued and safety wired you would be ok.

If you do any racing, a scatter shield is a wise investment. I've seen flywheels and transmissions fly apart and the damage they can do. A friend of mine was out of commission for 6 months when his trans let go. A very hot piece of nodular iron shattered his femur. Racing can be a very safe sport, so do not skimp on safety equipment.

DRCustom: You say hondas are for losers, but u seem to have a CRX urself correct? soooo...ummm...

enginerd is right with the scatter shield...

He's right with the scatter shield, but there's no reason to assume an aluminum flywheel won't be as safe as a moly or steel unit, assuming proper design. It's just a helluva lot easier to make the things really light using aluminum, plus you do have the added benefit of easily mating ring teeth metallurgy to the starter gear. Moly units not very well thought out tend to eat starter gears for lunch.

sarcasm - NOUN
1. A cutting, often ironic remark intended to wound. 2. A form of wit that is marked by the use of sarcastic language and is intended to make its victim the butt of contempt or ridicule. 3. The use of sarcasm. See wit. :D

Well, regardless of what type of material it's made of, I don't think I very much like the idea of molten metal becoming part of my anatomy.

Thanks for all the input, but where can I find a scatter shield, and how much can I expect to pay for one?

I don't believe anyone makes an off-the-shelf scatter shield for that car. STR and B&M are the leading manufacturers for Honda scattershields.

Plus the lighweight flywheel can cause a harmonic imbalance to the engine. Often an aftermarket harmonic balancer is required.

Originally posted by enginerd
Plus the lighweight flywheel can cause a harmonic imbalance to the engine. Often an aftermarket harmonic balancer is required.

Show me when a flywheel is used to balance a motor. I can't even conceive of how a perfrectly round, relatively flat disc is going to counter first or second order vibration on the bottom end.

I think that by "harmonic vibration" what he really meant was "harmonic" torsional vibration, which can be affected by the flywheel. Most notably, the vibratory mode shapes will be altered when a lighter flywheel is introduced, with the first-mode node moving farther from the tail end of the crank, etc. There will, of course, be an increase in the zero-order vibration as well (crank rolling motion), which is not such a concern for engine durability as it is for accessory durability and NVH.

That said, as long as the engine will idle (or at least stay running when you need it to) I don't think that changing the flywheel will result in big reliability problems in a 4-banger. With a longer crank I might be more concerned. The biggest troubles will arise if the vehicle is used as a daily driver, as the idle speed fluctuation of the engine may be unacceptably high (for accessory durability, timing drive durability in some cases, and general noise/vibration/harshness).

This topic brings me back to one that I've touched on in the past... "harmonic balancer" is quite a misnomer. The devices typically called "harmonic balancers" are more accurately described as torsional vibration dampers. They aren't intended to balance any kind of imbalance within the engine, rather they attenuate torsional vibrations.

I agree, most notable is the reduction in engine smoothness and NVH. The flywheel effect helps smooth out the power pulse delivery from the engine, which does reduce shock loading to the rest of the drivetrain. This is especially important in larger displacement, low cylinder count motors. Once you break the .5 liter per cylinder point, if the engine is a 4 cylinder this becomes an important constituent of overall feel.

You guys got it all wrong. Think of a flywheel as something that uses mechanical energy. It makes torque as it spins and this can keep an engine moving, lets say up a hill. The more weight the flywheel has the more "energy it harnessess" So if you got a heavy load going up a hill the GIANT flywheel can keep the engine moving under enormoous load.

The flywheel does keep the engine running smooth but no the same way a vibration damper does. A vibration damper twists to help relieve crankshaft torque.

The flywheel turns fast ok? Engines cylinders fire Independitly and on a big diplaced engine at idle you can really feel this? Now the flywheel takes its mechanical energy and in fact turns the engine. So the flywheel is turning the engine between and during firing of the cylinders which results in a smoother ride. Do you understand?
ITS ALL ABOUT PHYSICS MAN

So the lighter the flywheel the more acceleration you will have but not as good of a ride than a standard one.

um......no. A flywheel doesnt 'make' any torque, it just stores some torsional energy from the crank as angular momentum. This keeps the crank spinning around consistenly and smoothly. the lighter the flywheel, the less the engine has to work against it, so then it can shoot to the redline quicker. But it has its downsides too. If you shift to slow in a race, then the RPM's will drop down too quickly, and then you're not at your peak acceleration.

also, it isnt just weight, it's also speed and size that stores enrergy. you can have a really heavy small flywheel moving slow that'll store as much as a light wide one spinning fast. But you engine still has to power them both up. And they dont store THAT much energy. Flywheels in little toy cars are designed to keep it moving forward. Flywheels in real ones aren't. They are designes so that you don't feel every cylinder fire through your ass as you accelerate.

LoL Steel.. nice explanation there.. with the "They are designes so that you don't feel every cylinder fire through your ass as you accelerate."

Have you ever driven a big truck. Like a truck carrying a crane and a thounsands of pounds of tools and huge jacks. The flywheel will keep the engine moving because of the energy it gains before the hill. The angular momentum propells the truck. If you spin something then let it go it moves does it not? And it does make torque. Torque=radiusxtheta.

You also mentioned the Flywheel "This keeps the crank spinning around consistenly and smoothly." It moves the crank there you go. It making power so the engine does not have to work as hard and can fire without pinging.

Originally posted by The Dude
...And it does make torque. Torque=radiusxtheta...

First off, the equation for torque is not as above, but instead...

torque = F x L
where F equals force input, and L equals the length of the lever arm, from center to center connection.

So if you were to boil it down to pure physics, a flywheel does create torque. It's not in the way we normally think of energy generation when talking about cars, but the fact of the matter is that force is applied about a distance to the center of crankshaft rotation, which wehn input to my earlier equation clearly equals a torque output. That this force comes in the form of rotational inertia does separate it from downward pressure on the piston, but it is still a force applied over a distance which is rotating about a point, and is therefore capable of producing torque.

It's funny though because basically all of us hotly arguing this point clearly understand the basic physics at work, and although El Duderino (I'm not into the whole brevity thing) has definitely underestimated the knowledge of a few of us in terms of physics, his points do have validity.

So to save this thread from falling into the abysmal nature of argumentative responses, I'll just sum it all up as best I can. We've established that a flywheel preserves angular momentum in the form of rotational inertia (which increases by the square of the weight's distance from center), and that in doing so smoothes out the power transmission of the engine (which occurs in short, powerful pulses). This not only decreases crankshaft decceleration between pulses but also lowers crankshaft acceleration during pulses, meaning it literally flattens the power output of the engine to a smooth, constant force instead of a lumpy, sporadic mess. In doing so though it does take some force from the crankshaft which could otherwise be used to immediately accelerate the vehicle in question, and in doing so a heavier flywheel (all other things being equal) will have a small but measurable effect on accelerative ability, especially in the lower gears where increases in RPM occur quickly. The flipside is that lighter flywheel mass causes the engine to get lumpier in terms of power output, and the motor can change RPM quite quickly, which is not necessarily a good thing. How much you want of either set of attributes depends heavily on what your intended use is, which is why different cars and engine packages have large variances in flywheel weight. It's to accomodate their specific design and intended use as best as possible.

Originally posted by The Dude
And it does make torque. Torque=radiusxtheta.

hahahah really? last i checked it was force x lever arm. "How much torque is she putting out?" "Oh about 900 degree-meters" "SWEET"

;)

yeah, just listen to texan.. he's always right:)

You also mentioned the Flywheel "This keeps the crank spinning around consistenly and smoothly." It moves the crank there you go. It making power so the engine does not have to work as hard and can fire without pinging.

For something to make power, it first has to overcome its own inertia. I don't see how a flywheel does that. It keeps the movement of the crank smooth, it doesn't move the crank. Again, something that moves because something else is moving it doesn't make power. And what is pinging? Knocking?

lol. a flywheel keeps the rpms from accelerating quickly, at the same time, it keeps it from decelerating as well; it depends on the situation. If you accelerate to a certain speed and then let off the gas. The more angular momentum the flywheel has, the more energy it has stored and therefore you will travel a farther distance (if you had obtained the same speed with a lighter flywheel). So in essence, the flywheel is "pulling" the car along in this example.

On the other hand, the flywheel is also something that "holds you back". If at a given speed flywheel A has more angular momentum vs flywheel B, flywheel A requires more energy input to reach that very speed meaning the acceleration of flywheel A will be slower than that of B.

When the dude was talking about the flywheel pulling the truck up a hill. it's only PARTIALLY true, only up to the point that you reach the minimum speed at which you'd like to go up the hill. Conversely, if he wanted to increase his speed from the minimum speed at which he was travelling, then the flywheel is working against him.

If you simply understand that a flywheel has momentum, apply Newton's first law (an object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force) then you will see that there's really nothing to argue about.

Originally posted by Bryan8412


hahahah really? last i checked it was force x lever arm. "How much torque is she putting out?" "Oh about 900 degree-meters" "SWEET"

;)
Degree meters, I'm sure that'll be the next biggest thing out there, boosting your degree-meters from your engine.

For compariosn's sake, what is the average weight of a car's fly (Say a Toyota Camry) and a big Truck (Like freightliner or Mack) I mean, is this partly why trucks have such poor accelration other than the obvious factors. I mean lugging a huge flywheel around isn't aiding in the 0-60 time, but at 60 mph I bet it helps.

read the post above yours..

Ok, so does this mean that I shouldn't get the steel plate made because it will create a harmonic imbalace, or will it act as a torsional vibration damper? Or is adding this going to throw off my degree-meter calculations?

But seriously, I've heard of going off topic, but this is like woah...and to jump right in with a rampage...

Porshe- I would say that the flywheel does affect the acceleration of a truck. If a vehicle didn't have a flywheel, then it would barely idle (if even at all). Trucks do have large heavy flywheels to keep them going, they have to because they are so heavy. Think of the opposite: an F1 car. If you watch one drive off from a start, they ususally rev the engine really high, and spin tire. That is partially because they have a small lightweight flywheel. A truck needs it especially to get alot of weight going from a start (including it's own). It could use a lighter flywheel, but it would be hell on the clutch, and a bitch to drive. Noone complains because it's supposed to haul weight, and doesn't need to go fast.

Just for kicks, I think many passenger cars have around a 20 lb. flywheel. The largest I've heard of on a truck was around 60.
The one I have is about 6.5, the stock is supposedly about 18 lbs.

But...it's not just the weight of a flywheel. The size, and also where the weight is located will have different effects. Think of it this way, if you stand up and spin around with your hands held against your body, then it's pretty easy to stop spinning. If you hold your hands out, and try to stop, then it's difficult (you still weigh the same, but you're imitating a larger flywheel, with the weight twords the outside). If you hold weight in your hands, the it becomes even more difficult to stop (heavier, with the weight way twords the outside). So...you can have 2 flywheels, of the same weight and size, that act differently because the weight is more twords the outside.

A flywheel is used to store energy. Put a frisbee on a pencil's tip and spin it. It will be easy to spin, and will get moving fast quickly, but will be very easy to stop. It also won't stay spinning for very long if you don't stop it. Now take a large heavy disk, like one of those spinny things at a playgrond (sorry I forgt what they are called).
It's a mother to get that moving (compared to the frisbee), but once you get it started, it's hard to make it stop. That is because it 'stores' all of the hard work that it took to get it moving.

A heavy flywheel hurts 60 ft. times, but helps everything else. The only exception that I can think of is top speed (this is just a theory of mine, I really don't know). A ligher flywheel may lower top speed. As speed increases, so does wind resistance, and at some point that torque again becomes necessary to keep it trudging through the wind. I don't think that point is anywhere near 60 mph. I don't think it would become anything but beneficial unil way over 100 mph.

Just my .02, and I'm sorry about the novel, but I wish someone would have explained it to me sooner.

BTW everyone, thank's for the awesome posts.

Porsche- Most car flywheels are in the neighborhood of 20 lbs, while most truck motors get closer to 40 lbs. The reasons are obvious if you grasp previous postings.

DRCustom- Absolutely, weight distance from center does matter, which is why I included the formula for calculating distance from center vs. interial momentum in my first serious post.

Vehicular top has nothing to do with rotating mass, instead it's all about reaching an equilibrium between engine power output and drag. Mostly that drag consists of aero at any normal car speeds, but it's important to remember there is only one power source in a car. The engine provides all motive force, and while a very heavy flywheel could concievably change momentary peak speeds, it would have no effect on steady state maximum mph. The energy dissipated from flywheel momentum is siphoned off the crank, and in such an example there is ultimately no additional energy to siphon from the crank in the first place. So while momentum can play a short lived part in top speed, ultimately it's the engine's power output at a specific speed (relative to gearing) vs. a specific amount of total drag which determines steady state maximum mph.

Texan, that makes sense. Does this mean that top speed will actually increase? Or are you saying that when maxed out, the weight of the drivetrain is not relative at all? I am thinking this because would the power output of the engine in that situation be 'measured' at the weels?

Let's break engine function based upon load into two categories to better understand this: top speed and acceleration. What determines the accelerative ability of a car when you throw out friction, traction and gearing (for simplicity sake we'll keep those constant) is weight vs. power. Rotational weight in the drivetrain will certainly have a greater negative impact than weight carried by the chassis, so lighter engine internal parts, transmission and drivetrain pieces (including the wheels) will enhance acceleration, especially in the lower gears where engine RPM needs to rise quickly relative to vehicle speed. However, weight has nothing to do with vehicle top speed, which is what we are talking about now. The load put on the engine is certainly greater and therefore it will take longer for it to gain RPM and therefore accelerate the car, but vehicle top speed is always a function of gearing and friction vs. steady state engine power, none of which are directly affected by additional weight. You just have to realize that vehicle top speed and vehicle acceleration to that top speed are different beasts when breaking it down to basic physics, so what affect changing one will change the other depends upon what parameters you are playing with. In this case, weight is the one that has no effect on top speed but potentially a large one on acceleration. Altering aero drag instead has a potentially large effect on top speed but relatively little on acceleration, especially at lower speeds. Hope this helps explain things, peace.

It does help to explain. I guess I'm just having a hard time splitting those two beasts apart. Thanks. And if for some reason you just want to go ahead and explain more, please do, I love to learn.

damn, theres another page, i've had to delete all that typing

Originally posted by The Dude
You guys got it all wrong. Think of a flywheel as something that uses mechanical energy. It makes torque as it spins and this can keep an engine moving, lets say up a hill. The more weight the flywheel has the more "energy it harnessess" So if you got a heavy load going up a hill the GIANT flywheel can keep the engine moving under enormoous load.

I really hope you're being sarcastic. Less rotating mass=less resistance=less parasitic power loss=more power to the wheels. Aluminum is a very lightweight metal compared to steel, so an aluminum flywheel will offer less resistance to your car revving up. Very useful for high revving engines as it will let you climb up the tach faster, getting to your peak power faster as well.

Flywheel inertia cannot be considered a parasitic power loss, any more than a free savings account can be considered a waste of money.

In the most basic sense, the purpose of an engine is to convert chemical energy into mechanical energy. If you had your way, all the mechanical energy would be transferred to the kinetic energy of the vehicle, and it would coast indefinitely at whatever speed you picked (like an object in a perfect vacuum). Unfortunately, the real world conspires against us, and the mechanical energy ends up being dissipated in a variety of ways:
* aerodynamic drag on the vehicle
* friction and hysteretic losses at the tires
* internal friction of the drivetrain components
* pumping losses within the engine and accessories, such as power steering and air condiitoning
* production of electricity by the alternator (which is eventually consumed elsewhere)
* some others that don't come to my mind right now

In general, when people refer to parasitic power losses, they are referring to energy dissipation by components that are not necessary. Examples:
* power steering pump
* air conditioning
* electrical accessories
I would add to that list all of the friction losses within the vehicle, although many people don't consider those.

A flywheel stores mechanical energy, but it doesn't dissipate a significant amount (there is some slight amount of aero drag acting on a flywheel, but this is pretty insubstantial). When a flywheel speeds up, it is storing energy, and when it slows down, it releases this stored energy. This is how the flywheel keeps the engine running smoothly - when the engine speeds up, as when a cylinder fires, it must dump energy into the flywheel. The spike of power from the cylinder firing is largely absorbed by the flywheel, and the engine speed doesn't change much. When the engine wants to slow down, it has to slow the flywheel. The flywheel releases energy as it slows down, so again the engine speed doesn't change much. The flywheel doesn't actually dissipate any energy, though, so the net power output of the engine upstream of the flywheel is equal to the net power output of the engine downstream of the flywheel. The flywheel simply smooths out the mechanical energy tranfer, by absorbing the spikes and filling in the valleys. Calling a flywheel a parasitic power loss is, therefore, a whole lot like calling a (totally free) bank account a waste of money.

A lighter flywheel stores less energy at a given speed, and will allow faster changes in engine speed (both when revving up and slowing down). It will let you increase your rpm to a given speed more easily, but it makes it harder to maintain that speed. Having a very light flywheel can make your engine idle roughly (or not at all), and it can make it harder to get your car to start moving from a stop. If you are trying to make a car that will accelerate as rapidly as possible, and you have no other concerns about the drivability or ease of take-off, then a lighter flywheel will definitely help.

If you wanted to, you could make a car with no engine at all, that uses a flywheel to propel it. There are many toy cars on the market that use flywheels to store energy that the user inputs, and gradually release this energy to propel the vehicle. The little cars that you push a couple of times and release are an example. In a vehicle like this, a larger flywheel will result in more stored energy, and thus a longer running range. A larger flywheel can also result in greater acceleration, if the drive is appropriately designed.

The way I see it, if it makes the car go faster, then it must be improving upon a previous loss. For engines with peaky power output, the lightest flywheel possible would be best, allowing the engine to travel to peak power ASAP.

All depends on the nature of the engine.

Fair enough. There's no law that says you can't come up with your own terms for things. It makes communication more difficult, but I guess it can be fun too, and boy can it ever make you sound smart at a party! :alien:


Out of curiousity, do you also consider the mass of the vehicle as a source of parasitic loss? Or for that matter, your own bodyweight?

IVY all ready considered the mass of your vehicle as a parasitic loss ie: air, pow steering, and anything else that your car doesnt need to work properly. In regards to your body mass, it would be a loss because most of us have weight that we dont need

I'm not sure that I understand what you're saying.

I wouldn't call any energy storage a parasitic loss (because the energy isn't lost, it's stored). Vehicle mass, tire inertia, driver mass, etc., are examples of things that slow you down but AREN'T what I'd call losses. I guess that perhaps the more important thing for me to say would be "I think that it's incorrect to call these things 'sources of parasitic losses,' because they aren't places where power is lost."

I have a question - what accounts for the hysteretic losses through a manual transmission?

The vast majority of power dissipation in a manual transmission is through hydrodynamic losses and metal-to-metal friction. Anytime the fluid in the transmission is forced to move, some energy will be converted to heat. Anytime two metal components rub against each other, some energy is converted to heat. This mechanical energy that is converted to heat is the lost energy.

There are many interfaces where these two mechanisms occur; not all of the following interfaces are in all transmissions:

* roller bearings on shafts have metal-to-metal and hydrodynamic friction losses
* plain bearings on shafts have hydrodynamic losses
* hydrodynamic thrust bearings have hyd. losses
* gear-to-gear interfaces have both hyd. and metal-on-metal friction
* if the gears are partially covered in oil (splash lube setup) there will be hyd. losses
* if the oil is pumped through the transmission (forced lube), there will be hyd losses.

There is also a small amount of energy lost every time a shaft, gear, or gear tooth is loaded and unloaded. When components are loaded, they deform slightly, and when they are unloaded, they spring back. As they compress and spring back, internal friction sucks away a little bit of energy, so the energy released on expansion is slightly less than that absorbed on compression. Again, the lost mechanical energy is converted to heat. This is what is generally refered to as hysteresis (and hysteretic losses).

Did that answer the question, or did I miss the point?

Yup. Very well, actually.

Im having trouble making quick, smooth shifts. The RMPs drop too slowly. I think a lighter flywheel will make the rpms drop quicker when I pull out the clutch.

I get that aluminum aftermarket flywheel = less mass on driveshaft = less inertia smothing out power delivery and quicker revability.

Can someone tell me in simple words how putting a lighter flywheel on a daily driver will put stress on the engine or drivetrain? (2.4L four)

BTW: Anyone know if the flywheel on a SR20DET is compatible with the KA24DE?

I guess you're right in that the energy is stored, but unless it is perfectly stored (which never ever happens) i consider it a loss which may not be able to be cured but can at least be lessened.

And yes, an aluminum flywheel will make revs drop and rise quicker, but in your case perhaps a better mastery of your transmission may be a better cure (with much less cost).

Most of your aftermarket equipment is all hype, i wouldn't trust half of it.

A flywheel is about as close to "perfect" storage as you can get. The energy stored is returned almost entirely, and most of the places where it is lost are not affected by reducing flywheel inertia (a light flywheel will have nearly the same losses as a heavy one, in the same application).

Fliquer, a lighter flywheel is not the answer to the problem that I think you're describing. If your clutch is slipping when you engage it, you need to adjust (or replace) it.

Its not that my clutch slips, its that I want the revs to match the driveshaft speed. If I shift from 2nd to 3rd at 6000 rpm, I have to wait an entire second during the shift (with the stick in neutral) for the rpms to drop far enough (down to 5000) to make a smooth transition to 3rd.

If I throw it quickly from 2nd to third, I end up barking my tires or at least creating an unsettling jolt to the drivetrain. There is nothing wrong with my transmission, or my stick experience.

well if you want engine revs to drop quickly when you release the throttle in neutral, a light flywheel is the ticket.

I've never heard of someone with a synchronized transmission worrying about speed matching...

Yeah, i'm thinkin his synchros might be off.

i could cry, I wrote a friggin novel about it, and it didn't post. I got the flywheel in, and basically, I love it, it's great, and you should get one. I had a blowout and wrecked, so I'm not driving now. If I get time to post again, I'll try to write it all again.