I am thinking about buying a lightened flywheel. Does brand matter at all? Also does the weight matter? What i mean is can i damage the motor by using a flywheel that is too light? Also what are the advantages to using an aluminum flywheel compared to using a cromoly one? Is it bad to just have the stock flywheel lightened instead of buying a new one?


[Modified by Hayasa15, 12:06 PM 4/23/2002]

 

I've heard lightened factory flywheels can explode, sending shrapnel into the passenger compartment if you don't have a scatter shield. Most likely from high RPM clutch dumps. There was a post on this board from someone who now walks with a limp because of this. Buy a new cro-mo lightened flywheel. 4130 cro mo is strong as hell.

 

I am going to put a b16 into my civic. I am wondering if i can go too light. Will i lose too much torque? There isnt alot of torque to start with in these motors and i can you every little bit so should i go with a 12 or 13 lb flywheel or just go all out and get a 9 lb one? Also would anybody suggest not buying a flywheel of ebay, any bad experiences?

 

Fidanza

 

You won't lose torque, per say.. You know how the flywheel/clutch/pressure plate work together. So, If you are going to launch the car, with your stock heavy flywheel you put the revs at, say 4000. That heavy stock flywheel has more rotational mass. So that momentum built up at 4000 revs is quite a bit stronger than the lighter flywheel. The lighter flywheel can't "torque" the motor as well like that. So you have to raise the revs higher in order to get the same launch. It's the same sort of deal when you're just in stop and go traffic, you may have to slip the clutch a little more, or give it more gas.

Just as well, with the loss of rotational weight, you will shed some drivetrain loss, letting more power get to the wheels. Your car will drop the revs quickers between shifts. And your car will start faster and easier..

9 lbs is a little on the light side. Mostly reserved for fairly heavily built beasts that are far down the mod path. I'd stick with the 12 or 13 for better streetability.

If you're pushing a lot of power and a strong clutch, you might want to add a scattershield to your shopping list. It depends on how much of a risktaker you are. The odds are in your favor, but sometimes **** happens.

 

ive herd of some flywheels not mateing correctly with the starter teeth. would the fidanza or comptech cromoly flys work good with the starter?

 

The clutch/flywheel is on the passenger side of the car, so you would only really need a scatter shield if you plan to race with passengers. The orientation of the disc would not tend to throw pieces to the sides of the track either. They are still nice to have though.

 

I have a 7.5lb one from clutchmasters. I love it. It is not too light at all. I would not even consider a lightened stock flywheel. You can argue however that the mass of the flywheel ads a certan amount of damping to vibrations that could damage the crank or tranny or who knows what else. I don't really know about it, just throwing it out there.

 

how do you determine what weight or how light the flywheel suppose to be...I mean is there a ratio or something between the flywheel weight and HP/TQ?

where can you get a scatter shield? any specific brand?


[Modified by SamC, 7:12 PM 4/26/2002]

 

Thank you, to whomever it was (martini) that responded to the post explaining the effect of flywheels, rotating mass and launchability. Someone else finally had a good answer to this question. To summarize for those who missed:

FLYWHEELS DO NOT, REPEAT DO NOT, AFFECT THE TORQUE OF THE ENGINE.

Heavier flywheels making launching easier due to the increased energy storage, as explained above.

Lighter flywheels do in fact increase engine internal stresses, particularly timing belt/chain, balance shafts, etc. They also could prove problematic for the accessory belt drive. So there is a limit. The flywheel inertia (thus mass) is determined through studies of vibrations and other considerations. Increased torque is one of those considerations, as to maintain the same torque fluctuations experienced by the driveline, one would have to increase F/W mass with increased torque.

Edit: Found name of "whomever it was." Wanted to give credit where due.


[Modified by allenp, 8:48 PM 4/26/2002]

 

I fail to see how a lighter flywheel, all by itself, could effect internal engine components in a negative way. Granted, you are more likely to rev the **** our of your engine with a lighter flywheel, but how can a lighter flywheel (assuming balance is proper) have a negative effect on internal engine components? The reduction of rotational mass should result in less stress on internal components anytime other than when the inertia of the additional mass is helpful. I cannot imagine anything other than launching that would receive benefit from the additional mass. Once the benefit of the additional inertia has been absorbed (a fraction of a second after the clutch has fully engaged), the engine can only benefit from less rotational mass. Again, that is assuming that you do not rev the **** out of it as a result of the reduced demand of the lighter flywheel. I am open to an education here. If I am missing something, someone please educate me. Data and facts are much preferred over conjecture and heresay.

 

You're not missing anything man. It's just an old missconception

 

Okay, let me first substantiate my statements with my background. I am a degreed mechanical engineer with an automotive specialty. My current profession entails studying the vibrations produced by the internal combustion engine. I take in-vehicle measurements of such vibrations and apply them to the driveline for durability and NVH improvements.

I'm sorry you think my statements are conjectures or heresay. I cannot post the data itself, and the details require pages and pages of comments. I will try to explain however.

The internal combusion engine fires 1 cylinder at a time. Each time the cylinder fires, all rotating components in and around the engine (balance shafts, valve timing drives, front end accessories) as well as connected to the crankshaft (flywheel, clutch, transmission, etc) accelerate and decelerate with each combustion/compression cycle. If you look at a graph of speed over time of the engine, it will have a sinusoidal waveform. The more powerful the engine, the more severe the amplitude of the waveform. Additionally, the fewer the cylinders (and hence the lower firing frequency of the engine) the more severe the vibration. THIS is the reason the clutch disc has springs in it -- to absorb/dampen those vibrations before they get to the transmission. But that is another issue.

So where does the flywheel fit in? As an energy storage device, it stores rotational kinetic energy produced by the engine with each firing, and thus when the engine is in the compression cycle (the valley of that speed/time curve) it releases energy, bringing the valley up. Conversely, when the engine fires, it brings the peak of the acceleration down by soaking up some of the energy. The net result? A smoother waveform (lower peak-to-valley difference.)

As those rotating components accelerate and decelerate, they experience stresses. When load fluctuates like that, fatigue failures become a problem. Timing belts have broken as a result of engine torsional (rotational) accelerations. As have accessory belts. So, the engine designer needs to consider this.

The solution? A flywheel that smoothes out those accelerations as much as necessary.

Usually the flywheel is conservatively designed, so some lightening will likely have little long-term effects. However, severe lightening can.

 

ttt, this is important, commonly misunderstood info

 

You're speaking on lightening a stock flywheel. I could definetly agree that taking too much off of a stocker is looking for trouble. But are you saying that a flywheel that is much lighter than stock, (even if made with superior materials & designed to be just as durable as a stocker), is bad for the engine? I can't say that I have the credentials that you do, but with the timing belt & harmonic balancer in the crank pulley acting as dampeners, & our engines balanced as they are, I can't imagine a quality, aftermarket flywheel being detrimental at all.

$.02

 

I appreciate your response. All of this needs to be brought out.

No, I was not specifically speaking of a "lightened" stock flywheel, although that is a concern in itself. Lightening a flywheel by machining it is bad practice, as such a piece undergoes extreme thermal and mechanical stress during its operation. When a chunk of metal that big is spinning at 8000 RPM, you don't need any unnecessary stress raisers, which is what you get when you lighten it.

I am speaking of the total mass, thus inertia, contained by the flywheel. The "harmonic balancer" mounted to the crank, driving the accessories, serves VERY LITTLE purpose in storing energy and smoothing out the torsional (rotational) accelerations in the crankshaft. Its inertia is tiny when compared to the flywheel. All it does is smooth out the operation of the accessory belt drive.

Additionally, the "balance" of the engine as most people understand it has very little to do with the rotational accelerations that I mention. That balance refers to the linear accelerations, up/down, and rocking accelerations, back/forth, that the engine block/mounts experience as a result of the firings and piston motions. The fluctuations I speak of are strictly rotational, and are primarily a function of combustion/compression cycles.

When those combustion/compression accelerations increase, as a result of an increase in engine torque, or reduction in flywheel mass, the stresses experienced by everything rotationally connected (thus powered) by then engine increase. Usually not to a degree that things break, but fatigue is accelerated. I have read reports from my company, as well as the OE automakers, stating that failures of timing equipment and accessory drives can be directly attributed to the reduced mass, thus inertia, of the flywheel.

[Edit: Clarifications]


[Modified by allenp, 4:15 PM 4/30/2002]

 

OK, what you said makes alot of sense. My question is what about a flywheel with an average mass, but less rotational inertia. ie a flywheel that has more of its mass towards the center, and less around its edges. Like if it had holes or slots around the edges, not enough to take away from its structural integrity though. That way it would have a normal amount of mass, but would be much easier to spin so that the engine would benefit from not having to work as hard to get it to rotate. Or am I wrong, and is it the rotational inertia that helps attenuate the instantaneous angular accelerations of the engine?

 

quote: "Or am I wrong, and is it the rotational inertia that helps attenuate the instantaneous angular accelerations of the engine?"

You are correct in predicting your incorrectness: it is the rotational inertia that does the job of dampening the accelerations. So, any reduction in overall inertia, as measured at the crankshaft, will increase the stresses.

However, I hope that the manufacturers of these lighter flywheels, besides verifying the integrity of the part, have done their homework and made sure that the engine will respond well to the increased stresses. Reputable manufacturers probably have.

Reducing flywheel mass/inertia has many consequences, not many of them good. By reducing the material at the outer diameter by thinning, this is typically where most of the heat generated by your clutch is absorbed. So, you increase the thermal stresses and potential warping problems. By drilling or slotting at the OD, you introduce stress raisers at the highest-stress area of the flywheel. As you go out radially, the rotational velocity increases, and so does the centrifugal force.

Please understand that my statements are backed by actual research done by myself or my employer, a major OEM clutch/flywheel manufacturer here in the US. They are NOT conjecture or heresay, and I am simply trying to dispell misleading and potentially hazardous misconceptions.

[Edit: Clarification]


[Modified by allenp, 4:53 PM 4/30/2002]

 

Thanks for the knowledge.

I think it's important for everyone to note that pretty much everything we do to our cars to make them faster, has a negative effect on the longevity of the engine. So don't read this thread & go tell people that their engine will explode if they get a lighter flywheel. Instead, educate them to what we have read here. Everyone who installs a larger cam should know that the larger lobes increase the stress put on the valve springs... lust like everyone should know that a lighter flywheel increases the stresses put on pretty much all internal components of the block.

 

Thank you for taking your time and explaining to us. I learn something new everyday.
jason phan

 

Glad to share. This is one topic that I can talk quite a bit about!

You make a good point: As one modifies the engine, stresses are increasing. Usually, this isn't a problem... To a point. What is important, from my perspective, is for everyone to understand what they are doing. Flywheel function is widely misunderstood -- I've been a car guy forever but until I started working with them, I didn't truly understand.

 

my brain......................hurts...

 

clutchmaster makes a cool flywheel the contact pad is removable so if you glazt your flywheel you can just buy a new contact pad and not a new flywheel saves you some $

 

Great info! [golf clap]

 

jun superforged is nice. i love the tech area...


[Modified by madeinjapan, 7:23 PM 5/4/2002]