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Hello,
Does anyone out there have any experience with changing over to a light weight fly wheel? My buddy keeps talking to me about how it changes the nature of the car in a positive way and increases horse power. Though I don't understand how...

So, if anyone out there has any anecdotal or even factual information about their experience...Negative or Positive

I would love to hear about it

DC
 

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I did it recently. Not many miles yet but the feel from stock, as far as driveability, is negligible.

Correct me if I am wrong: It does not increase horsepower. Rather, more horsepower goes to the wheels because it is not used up spinning the heavier stock flywheel.

If you do go that route you MUST use a sprung clutch disc vs. the stock rigid disc.
 

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I put a LWFW in my 987 Cayman S (early 3.4ltr motor) and it did change the way the engine responded. It CAN'T increase HP, period. Your engine is producing as much HP as it can, and changing the weight of the flywheel doesn't change the HP. But just as the Sport button (or a throttle remapper like the Sprint Booster) change the way the power delivery feels, so does a LWFW. For me, it was the biggest single change that I made to a car I made nearly every modification to (cat back, intake plenum, ECU remap, suspension, etc.) It *felt* like the car had more HP, but it didn't. The engine seemed to want to rev more freely, and spun up faster. (I never had a problem with stalling, which some people say is a downside. There's also those who say that a LWFW will cause the crankshaft to explode...but I didn't listen to them. LOL)
My GT4 has a factory LWFW and I can certainly notice it. The engine is a real happy rever, for sure.
 

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It *felt* like the car had more HP, but it didn't. The engine seemed to want to rev more freely, and spun up faster.
It felt like it had more horsepower because it did. :) Not because the engine makes more, but because, as mentioned above, more is available to turn the wheels and it's simply easier to rev up the engine. All those things you're mentioning are exactly why people do this mod. :)
 

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I have an 11 lb Aasco aluminum flywheel in my 981. John at BGB installed it. Gave me a 25 lb-ft more torque. Motor revs very fast. One of my favorite upgrades. Hopefully John will chime in on this thread. We had a really interesting discussion on flywheels a few weeks ago.
 

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Discussion Starter #6
Sounds great...

With regards to mods you have done to your cars, where would you rank this ?

Any negative effects because of the flywheel? Drivability? Dependability?

How long or how many miles have you put on after changing the flywheel?


Sent from my iPhone using Tapatalk
 

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No effect on drivability. Second favorite mod after LSD. Also added Cargraphic headers and 3.8L engine. 6k miles since adding mods. Next time I will add a springed clutch.
 

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It felt like it had more horsepower because it did. :) Not because the engine makes more, but because, as mentioned above, more is available to turn the wheels and it's simply easier to rev up the engine. All those things you're mentioning are exactly why people do this mod. :)

That's Canadian logic for ya! The power output of the engine is unchanged by the flywheel, what is changed is how easy it is for the motor to move from one RPM to another -- in other words, its responsiveness. Of the many hot rod BMWs I've built, the single most enjoyable mod was the LWF, period. HP is great, but responsiveness is better. That said, it's costly if you're not doing a clutch or rebuilding an engine, as you have to yank the transmission out to put it in (except maybe in Canada!).
 

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That's Canadian logic for ya! The power output of the engine is unchanged by the flywheel, what is changed is how easy it is for the motor to move from one RPM to another -- in other words, its responsiveness. Of the many hot rod BMWs I've built, the single most enjoyable mod was the LWF, period. HP is great, but responsiveness is better. That said, it's costly if you're not doing a clutch or rebuilding an engine, as you have to yank the transmission out to put it in (except maybe in Canada!).
My logic is solid. :) The reason the engine is more responsive and revs easier is because you need less power to spin the lighter flywheel. That's obvious, right?

When I say there's more power available, I'm talking about power to the wheels. Yes... the engine isn't producing more power, but there's now less drivetrain loss. The power you FEEL and that's used to move the car is that at the wheels, and there will be more of it with the lighter flywheel.

You should see this quantitatively on an actual dyno, to back up the butt dyno. :)
 

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What is the stock flywheel weight?

I wonder why Porsche didn't install from the factory the lightest flywheel possible in a sports car like 981? If aftermarket 11lbs does great and brings no stall issues...
 

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To Wild Weasel. I haven't seen any impact on the dyno charts from a LWFW. Let's see if we can find evidence to support your contention. As I said, it was the best (of many) mod I did on my 987, and I can feel it in the GT4 (I've also driven GT3RSs which have a factory LWFW and noticed it there too.) But to say it increased WHP is an empirical question that can be answered by producing a dyno chart. I'd like to see one, that's all.
To T-Design, I think the stock (987) FW weighed about 28 lbs, and the Aasco I installed weighed about 14lb. AFAI remember.
 

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My logic is solid. :) The reason the engine is more responsive and revs easier is because you need less power to spin the lighter flywheel. That's obvious, right?

When I say there's more power available, I'm talking about power to the wheels. Yes... the engine isn't producing more power, but there's now less drivetrain loss. The power you FEEL and that's used to move the car is that at the wheels, and there will be more of it with the lighter flywheel.

You should see this quantitatively on an actual dyno, to back up the butt dyno. :)
No, I don't think that's true. The power remains the same, inertia doesn't. The power is not lost in the drive train. Once the motor is humming at 4000 rpm, it produces the same HP, regardless of flywheel weight, and the same power is at the rear wheels -- that's the flaw in your logic.

Power lost in a drive train is a different concept, where it takes power to turn the transmission and differential and overcome the friction of the wheel bearing. But, with or without the LWF, 3.5 rpm will always produce the same power at the rear wheels. At 4k it will produce the same power. The ability to get between those two points will be easier because of less mass, making the illusion of more power....

By gross example, say BMW uses same motor in two cars, one weighing 3500 lbs, the other weighing 4000. 0-60 time is quicker (assuming same gearing) on the lighter car, but motor is unchanged and the heavier car does not absorb power, having less at the rear wheels. The horsepower remains the same.


EDIT: Dr. Phil posted his response while I was writing mine and it brings up a good point. If there was evidence supporting this novel theory (I won't say Canadian theory), tuners would sell LWF as a power-increasing mod. They don't. Why? For the simple reason there is no power increase from it. They can't claim more HP with LWF, so they don't. If they could, they would!
 

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I wonder why Porsche didn't install from the factory the lightest flywheel possible in a sports car like 981?
I would like to know the answer to this as well. I'm no engineer, but it seems to me that engineering is about finding the right "balance" of things (cost vs efficiency vs mtbf vs performance etc). Wouldn't a lighter flywheel cause more vibration and shorten the life of other engine components? Wouldn't Porsche have already calculated the minimum acceptable mass for the FW?
 

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No, I don't think that's true. The power remains the same, inertia doesn't. The power is not lost in the drive train. Once the motor is humming at 4000 rpm, it produces the same HP, regardless of flywheel weight, and the same power is at the rear wheels -- that's the flaw in your logic.

Power lost in a drive train is a different concept, where it takes power to turn the transmission and differential and overcome the friction of the wheel bearing. But, with or without the LWF, 3.5 rpm will always produce the same power at the rear wheels. At 4k it will produce the same power. The ability to get between those two points will be easier because of less mass, making the illusion of more power....
I'll start by saying that I'm pretty sure I'm right here but am now just as interested in you are in seeing any sort of proof of it. My theories right now are just that, based on my understanding of how it all works.

You mention the drivetrain losses including the power needed to turn the transmission. I don't see any reason this is different than the power needed to turn the flywheel.

Yes, at a given RPM, the engine will produce the same power. But to put that power to the wheels, it must also increase the speed of the flywheel. That uses some power that would otherwise be available to turn the wheels.

I don't think this is an allusion of more power. It's actually more power at the wheels, though obviously not at the crank. The flywheel is between the crank and the wheels. :)

The analogy of cars of different weights doesn't apply. You need more power to move a a heavier weight.... but doing this uses power at the wheels. So the same power at the wheels will yield different results for different weights. This means that reducing the weight will give better performance, but the power at the wheels as measured on a dyno should be identical.
 

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I'm with WW on this one. It seems pretty straightforward that lighter flywheel will make a measurable difference on acceleration. Take a toy car, and push it to coast across the room. Now attach a serious weight (to make things obvious) to one of the toy car axles. Like wrap a piece of lead around the axle. Same push will not get it to the same speed at all. Because some of the energy is used/wasted to spin that extra weight. Now, in a real car the effect will be much smaller, but it'll be there all the same.
 

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I'll start by saying that I'm pretty sure I'm right here but am now just as interested in you are in seeing any sort of proof of it. My theories right now are just that, based on my understanding of how it all works.

You mention the drivetrain losses including the power needed to turn the transmission. I don't see any reason this is different than the power needed to turn the flywheel.

Yes, at a given RPM, the engine will produce the same power. But to put that power to the wheels, it must also increase the speed of the flywheel. That uses some power that would otherwise be available to turn the wheels.

I don't think this is an allusion of more power. It's actually more power at the wheels, though obviously not at the crank. The flywheel is between the crank and the wheels. :)

The analogy of cars of different weights doesn't apply. You need more power to move a a heavier weight.... but doing this uses power at the wheels. So the same power at the wheels will yield different results for different weights. This means that reducing the weight will give better performance, but the power at the wheels as measured on a dyno should be identical.

I understand exactly what you're saying, but I think you're using the wrong terms. There does have to be a measurement of how much power it takes to change a motor running at 3.5k rpm to 4k. And with a LWF that measurement is less, no doubt. But it is not HP -- or at least not as we normally use the term. I don't know what that measurement is, but if the LWF resulted in a raw HP gain every tuner would sell it as such. But none do.

Think about it. At 4k, regardless of the flywheel, the engine produces X horsepower, but your theory is that in between that speed and another there is power loss. Compare with drivetrain loss, where the power is lost constantly. Logic tells you that these are two different things.

If you're right, find the data to prove it. You know it would be out there, easily accessible, if true. But I have never seen it after geeking on cars more years than I care to admit (only 40+). As stated above, I don't agree with your logic that the measurement you're looking for is what we civilized folk call horsepower. But, as a peace offering, since I agree it is a measurable phenomenon, we can call it "weasel power."
 

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I'm with WW on this one. It seems pretty straightforward that lighter flywheel will make a measurable difference on acceleration. Take a toy car, and push it to coast across the room. Now attach a serious weight (to make things obvious) to one of the toy car axles. Like wrap a piece of lead around the axle. Same push will not get it to the same speed at all. Because some of the energy is used/wasted to spin that extra weight. Now, in a real car the effect will be much smaller, but it'll be there all the same.

Your example is wrong because the horsepower is unchanged by putting more weight on the toy car, what is changed is acceleration.

I did WW's work for him and here is the link that explains that HP is unchanged but acceleration isn't -- or, as they put it, virtual power. I prefer weasel power, but to each their own:
How a lightweight flywheel works
 

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Dr. Phil and inkatouring are correct. A LWFW reduces the polar moment of inertia which lets the engine accelerate (rev) more freely. It won't have an affect on steady state power output. The result is a more responsive feeling engine and some improvement in the acceleration of the car as less power is being expended to spin up the fly wheel but at any given rpm total power won't change.
 

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Your example is wrong because the horsepower is unchanged by putting more weight on the toy car, what is changed is acceleration.

I did WW's work for him and here is the link that explains that HP is unchanged but acceleration isn't -- or, as they put it, virtual power. I prefer weasel power, but to each their own:
How a lightweight flywheel works
I didn't say horsepower changed. Of course engine is an engine is an engine. All I said is that I agree with WV that lightweight flywheel should and will make measurable difference in dynamics of the car.
 
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