Aluminum Flywheel

Most serious racers go with lighter flywheels or lighten their steel wheels, (not cast iron ones). The benefit of reducing flywheel weight is that it enables the engine to change speeds faster. This is perceived as a more responsive engine.

I had about half the weight, of my 308 wheel machined away and it is noticeably quicker revving, (16 pounds to about 8 pounds).

There is a mistaken assumption that this changes the engines torque, it does not, it simply allows the engines output to more quickly be applied to the drivetrain.

If you go to low with the flywheel weight, you may find the car stalling more often on starting out from a stop. It takes some getting used to. I had an auto-x 914-4 with a lightened steel wheel and a 911s Aluminum pressure late, (sprayed chrome face for durability). Because of the low rotational inertia of this assembly and the highly cammed engine, (low power at low rpms), if would occasionally stall taking off.

I believe that the aluminum wheel needs a bolt on steel insert for the wear surface or to have a chrome facing sprayed on, as the porsche factory did for the 2.2 911s.

If you have a chance, drive a car with a lightened/aluminum wheel - you will notice a difference.

hth,
chris

 

There's no impact on reliability. It's a worthwhile mod. Your engine will rev up faster, and your rpms will drop back down faster. You'll put more of your existing horsepower to your rear wheels. It is a noticeable improvement.

You'll probably even be able to sell your OEM iron flywheel for more than what you paid for your custom racing aluminum replacement.

 

Nope, sorry.

HP is the ability to maintain a constant veocity,, where as torque is your ability to change velocity. All you are doing by lightening the flywheel, is reducing the polar moment of inertia, of the entire rotating mass. (Not a Bad idea.)

I will be using a custom lighter Steel flywheel for my Mondial 8..
and One of my Aluminum pullies (For sale,for a 308 or 328)




Edwardo

Ciao,
Edwardo
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I have a mate that is a machinist at an engine shop.

He machined nearly half the weight off his flywheel from his old 253ci V8 engine. Anywho, we refitted it after he machined it and you could tell the engine revved faster afterwards.

Was a pretty cool experiment. That engine should still be used as a boat anchor IMO.

 

This is actually true. I don't have the dyno sheets handy, but on one of my Ducati racebikes we ran probably 300 dyno runs over a two year period.
At one point we were making a consistent 90HP at the rear wheel. We would make an all gear run (from 1st thru 6th), pulling to redline of 9500 RPM, and we would see 65HP in 1st, 75 in 2nd, 80 in 3rd, and then 90 from 4th thru 6th. After I changed to a lightened flywheel and a light clutch, we did back to back runs. Then we saw 75HP in 1st, 83 in 2nd, and 90 from 3rd thru 6th. So even though I was not making any more HP, we were getting more power to the ground sooner.

 

Fantom HP.. Magic HP.....??? LOL
What ever, , your dyno was probably calibrated on some motor,,, at some RPM,,, measure your fuel flow,, or pfffft,,,, on your efficiency and HP equations.
Back to school now all jr. Engineers.
Unless you were running the engine richer,, with boost,, you had the same HP.
Edwardo

 

A Btu is a BTU is a BTU.
Now back to school. again.

Edwardo

 

Yes, but BTUs that you don't use to turn a heavier flywheel are available to be used on downstream at your rear wheels.

For a mental experiment, imagine the opposite extreme, a flywheel with a two-ton mass...very few BTUs would be left after turning that massive flywheel to be available to turn your rear wheels.

As you dropped that massive flywheel from two tons down to one ton, more BTUs would be available for the rear wheels. Drop it down to half a ton, even more BTUs would be available.

Same BTUs coming from the engine, but more would make it past the flywheel, into the rear wheels.

Lighter is better.

 

Personally I've never been a big fan of lightened flywheels. Sure, your motor might rev a touch faster, but a flywheel is designed to store rotating energy. Anything you lost in revving due to a heavier flywheel is gained back on the first shift (as compared to a lighter flywheel). Yes, less rotating mass is good at higher RPM's. However, don't forget, with a lighter flywheel, your motor may tend to bog a bit when you end up shifting at lower RPM's.

It's always a trade off. There's no free lunch.

Ray

 

Lighter is NOT better. It that were the case, car manufacturers would supply very light flywheels. That's like saying stiffer springs are better or thicker anti-roll bars are better. A generalization. An over simplification. It is simply a different compromise. There are negative effects caused by light flywheels. It depends on the application etc.

 

If you like running the car very hard through the gears, I would take a long look at the aluminum flywheel. The steel will retain a lot of rotational inertia as previously posted which is transfered through the drivetrain to the wheels. If the tires spin when the clutch is released, some of that inertia is left as a rubber patch what many call "barking the tires". If the tires hold, the drive train has to take all of the hit. That "barking" sound is considered by many to be cool but it will eventually reward you with breaking a weak link in the car and emptying your wallet. BTDT with previous domestic muscle cars (been there done that). The other posts hit the nail on the head with easier to stall on initial launch, quicker revs and faster shifting. In the short time I've been on this forum I've developed a genuine respect for the info they share.
Thanks for considering my opinion. UncleRay

 

The mass of a flywheel has no effect on the torque coming from the crank, but removing mass from a flywheel will increase the torque available to rotate other masses downstream. Torque provides rotational acceleration to a mass. If there is less mass to accelerate at the flywheel, an additional amount of corresponding torque is passed on to the drivetrain. Removing mass from a flywheel will result in an increase in torque, and thus horsepower, at the wheels.

 

a big difference!

I put one in my modified 300zx before I did it in the Ferrari. I could not believe how fast it revved. It was noticeably much faster! Same with the Ferrari. It revs much quicker than stock. Throw in a Kevlar clutch and you have a good combo.

Cheers

 

OK, moving beyond the pros-cons of the science for a second, what's a recommended source for an aluminum one? Who machines the steel OE's?

 

Sorry, but I have to disagree with you.
Torque and HP are two different animals and are produced in different ways.
The flywheel is essentially a device that stores torque and it is necessary to smooth out the running of an engine that produces torque in a non linear way.
Motorcycle engines are a good example: single cylinder = heavy flywheel; more cylinders = lighter flywheels.
A lighter flywheel will store less torque, but the amount of torque being produced and HP will remain the same.
The engine will go up to revs faster, thus giving you the impression there is more HP, but max rpm and HP will be exactly the same.
On take off you will need to use the clutch more than before, because there is less torque stored in the flywheel to help out in getting the vehicle moving.
If you reduce the weight of the flywheel all the way to zero, the engine will become intractable and pretty much useless.
If you increase the weight of the flywheel instead, the torque stored in it will give you the impression the car is being catapulted forward, when you take off, similar to how a diesel engine feels, but again top RPM and the HP will be the same as before.

 

Every time you accelerate an engine - every time - it must consume air and fuel to make it turn. The engine must pull the air in, compress it and push out the exhaust, it must turn the alternator, water pump and oil pumps and it must accelerate the mass of the rotating compnents. these are parasitic losses.

So, you acceleate the engine through first gear, the engine must expend power to rotate that flywheel, (and other stuff) before it can rotate the wheels if you reduce the work the engine must do, you will have more left to make the car go.

The principal issue is acceleration not steady state maximum grunt at peak hp, it is the speed with which you can get to peak hp.

Pretend you are an engine, rotate a large heavy wheel up to 20 rpm, now, try to get to 30 rpm as fast as you can - think about it, if the heavy wheel only weighed half as much, you could get it to 30 rpm faster couldn't you. Now, do this exercise through a transmission, a bazillion times, and you will be screaming for a lighter wheel

My engine told me so
chris
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Excellent description. Bravo!

 

But still Wrong, wrong & wrong.
And, if you still believe this,,
Check THE 1st law of thermodynamics,,
or did all of you skip that day in college..?

Edwardo
BS Mechanical Design, Cal Poly SLO

 

Bingo! There is only so much horsepower and torque. You can't make it by lightening a part.

What you can do is make it more "quickly usable" by lightening the rotating mass. A lightened flywheel will help you row the gears faster. You'll use up that horsepower and torque more quickly. Which is important in a performance/track/race car.

But, you sacrifice some smoothness and drive-ability of the motor. Which is important in a daily driver.

Rick

 

ummm.... lets see if I remember it the way my favorite prof interpreted it.

You can never win, you can only break even
You can only break even at absolute zero
You can never get to absolute zero

Rick

 

It's not wrong. Every drive-train has losses. Put your car on a dyno and most will estimate your crank hp by factoring in a 17% loss of transmitted power (through your drive-train).

Your engine puts out 100% of your car's power. If your flywheel is heavy enough to absorb 4%, then only 96% of your motor's power is left to travel through the rest of your drive-train to finally make it to your rear wheels. If the rest of your drive-train saps 13%, then your rear wheels are only recieving 83% of the power that your motor made at the crank.

But...if you go to a lighter flywheel, then you might reduce the flywheel loss to 2%. Of course, the rest of your drive-train is still sapping 13%, but now 85% of your engine's power makes it to your rear wheels.

The total power from your engine never changed, but the amount of hp delivered to your rear wheels *does* increase as you lighten your flywheel, per the math.

 

source: http://www.rogueengineering.com/Merchant2/merchant.mvc?Screen=CTGY&Category_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.). "

 

I'm thinking that you are hung up on semantics?

 

Edwardo, somebody needs to go back to school, how are you fixed for tuition???

You are thinking about steady state horsepower. In this case we are not talking about steady state horsepower, but the horsepower delivered in terms of the ability to accelerate the car, which is a funcition of the TORQUE delivered to the driving wheels.

While the power produced by the engine is thermodynically the same, DURING ACCELERATION the torque delivered to the rear wheels is increased with a lighter flywheel because some of that torque isn't being used to put energy into the flywheel. Remember the equation torque = I (inertia) X alpha (acceleration). If you want to accelerate anything the inertia and the rate of acceleration determine how much torque it takes to do the acceleration. Reducing the mass of the flywheel has the same effect as taking mass out of the vehicle, and consequently results in faster acceleration.

Some chassis dyno's measure horsepower delivered as the ability to accelerate a large mass drum. In that case the horsepower (as measured in this dynamic environment) will show an increase if a lighter flywheel is used since the torque available is actually increased. Thus, while the engine doesn't actually produce more thermodyamic horsepower at a given steady state speed, the horsepower of the engine, as measured by the ability to perform acceleration is actually increased because you are measuring it in a dynamic environment.

Somebody needs to go back and take a few classes in dynamics...

Now I know what schools to avoid when I hire more engineers....

Manny.... MS of Engineering Univ of Fla...