Flywheel weight reduction?

[Matt Timion]

I'm a bit new to the car scene. Admittedly, I only learn what things do on the car when I'm about to modify them. I had no idea what a throttlebody was when I bought a new one for a project. I had no idea what fuel injectors were until I took a good look at the intake manifold (intake manfold, what's THAT?!?!)

Anyway, I have no idea what a flywheel does.

I do know, however, that it's one of the things the engine spins constantly. Just like the tires, spinning weight is the first thing that needs to be reduced. Even if the weigh reduction is fractional, it will then require the engine to work less to move the same parts, thus enabling you to get lower RPMs at the same speeds, and therefore giving you a much more fuel efficient vehicle.

So how much can you reduce the weight of a flywheel? I will be throwing in a new transmission with my new engine once they all get here. While I'm there I will be throwing in a new clutch and flywheel so that I don't ever have to worry about either of those things going bad on me.

The question is, how much can reducing flywheel weight help? In my situation it will be impossible to test the effects of EVERY modification I make (I'll be making at least a half dozen modifications total, so it's impossible to test for teach variable). Also, how much weight can be removed from the flywheel? I'm assuming they make racing flywheels for this very reason. Is the extra cost of the lighter flywheel worth the potential savings?

[SVOboy]

The lightest out there is really 7 pounds. That's the best you can get. Is it worth it for the money based on mpg increases, nope. Not by a long shot I don't think, especially if you get one new.

Here is some crap:

<a href=http://www.geocities.com/MotorCity/7177/flywheel.html target=_blank>Flywheel Lightening</a>

Last year I had a physics problem. It was if you had a 1000kg flywheel, and you got the car up to speed and it spinning at whatev speed, you could shut the car off and travel on the momentum for kilometers and kilometers, they store a lot of energy in them.

[Matt Timion]

So basically what you're saying is that while the lightweight flywheel may help you accelerate faster, it is only good for short distances? (ie, drag racing, etc.)

Wouldn't the flywheel for "coasting" be irrelevant considering that we coast in nuetral?

[SVOboy]

The flywheel weight will affect it most when you are city driving, because on the highway it takes very little kinetic energy to overcome the coefficient of friction working on the flywheel, so in that case, it makes less difference, but for stop and go it'll have more impact. But there is also the idea that 20 is not so small weight wise and why not kill it anyway.

[Matt Timion]

Originally Posted by SVOboy

The flywheel weight will affect it most when you are city driving, because on the highway it takes very little kinetic energy to overcome the coefficient of friction working on the flywheel, so in that case, it makes less difference, but for stop and go it'll have more impact. But there is also the idea that 20 is not so small weight wise and why not kill it anyway.

I think for a race car that makes sense. People spend $400 on a carbon fiber hood just to lose 20 pounds or so. With those race cars, every pound counts.

Now, is it worth it to spend $300 on a new clutch and flywheel just to lose 20 pounds or so? Considering my entire engine costs $350, I'm not so sure $300 for a clutch and flywheel can be justified. Maybe I'll just use my old one.

[SVOboy]

I'm thinking I'll pick up a oem one and take it to a machine shop and have it lightened a bit, or mehbe find a used one cheap. Or something, I dunno.

[chasgood]

Originally Posted by SVOboy

The flywheel weight will affect it most when you are city driving, because on the highway it takes very little kinetic energy to overcome the coefficient of friction working on the flywheel, so in that case, it makes less difference, but for stop and go it'll have more impact. But there is also the idea that 20 is not so small weight wise and why not kill it anyway.

I other words it takes less energy to keep something in motion than to start something in motion.

[SVOboy]

That's basically how it works frictionally with something like that. That would be the only thing requiring added energy in the rotational motion. But the thing that really makes it hard to get started is the inertia that is possessed by the damn thing. I could do the physics to decide the actually difference if you want?

[SVOboy]

Just the other day I ran across a post somewhere where someone had bought a lightened flywheel and claimed that they could actually see a mpg difference, though they were unsure if it was driver or the flywheel.

[Matt Timion]

Originally Posted by SVOboy

Just the other day I ran across a post somewhere where someone had bought a lightened flywheel and claimed that they could actually see a mpg difference, though they were unsure if it was driver or the flywheel.

This is a common problem with MPG tests. There are so many people that claim to have noticed a difference. Usually these people will give a range of percentage points (I had a 4-7% increase!)

So sorry, but a 4-7% increase PROBABLY isn't statisically significant, especially for one driver. If you had 20 drivers and a collective difference of even 4% it would probably be statistically significant. For one driver? No way.

Too much of this gas mileage testing is done by people with no data gathering experience, and no real understanding of the experimental process.

Really the best way to do it would be to not tell the driver that things have changed and record mpg. then again, it would also be better if you could do an A-B-A test, where you test without the modification, WITH the modification, and then without it again to see if there is a drop. Of course, doing a blind study would be the best way to do it too, but I never forsee anyone having enough money to properly conduct experiments for fuel additives, flywheel weight, and other small things.

[dfoxengr]

Originally Posted by Matt Timion

Now, is it worth it to spend $300 on a new clutch and flywheel just to lose 20 pounds or so?

but you have to remember that rotating mass is more than unsprung mass.