How many horses would a light flywheel free up
05-12-2006, 04:10 AM
#26
Greek Power
Join Date: Jul 2003
Location: Greece
Posts: 439
Likes: 0
Received 0 Likes
on
0 Posts
Come on guys, it's plain physics: T=L x F, while F=M x g. Decrease M, you decrease F, you decrease T, which simply means you need less power to spin the lighter flywheel (smart, heh ? 
).
In theory and in practice, by installing a lighter flywheel you don't increase the crank HP, but you certainly increase the percentage of this HP/torque that reach the wheels, i.e. you increase WHP.
So, a lighter flywheel does not increase crank HP, but certainly increases WHP
And of course allows the engine to spin up faster, since its reduced mass proves less of an obstacle (less inertia)
).In theory and in practice, by installing a lighter flywheel you don't increase the crank HP, but you certainly increase the percentage of this HP/torque that reach the wheels, i.e. you increase WHP.
So, a lighter flywheel does not increase crank HP, but certainly increases WHP
And of course allows the engine to spin up faster, since its reduced mass proves less of an obstacle (less inertia)
05-12-2006, 07:59 AM
#27
Rotary Wanker
It is plain physics but you're confusing energy with power. A flywheel is an energy storage device, it doesn't create, absorb or provide power. If you had NO flywheel, the horsepower delivered by the engine to the rear wheels at a given RPM would be the same (minus the frictional losses in the drivetrain and assuming you could keep the engine running). The improvement comes from allowing the engine to spin up quicker (which the lighter flywheel allows) which translates to HP being available earlier. In the end, the maximum horsepower (heavy flywheel, light flywheel or no flywheel) remains the same.
Reducing flywheel weight just re-shuffles the existing horsepower throughout the RPM range. If you really think that reducing flywheel weight increases RWP, then you should concentrate on reducing the weight of the wheels, tires, brakes and other rotating machinery in the driveline. Those items weigh an order of magnitude more than a flywheel.
Reducing flywheel weight just re-shuffles the existing horsepower throughout the RPM range. If you really think that reducing flywheel weight increases RWP, then you should concentrate on reducing the weight of the wheels, tires, brakes and other rotating machinery in the driveline. Those items weigh an order of magnitude more than a flywheel.
05-12-2006, 08:49 AM
#28
Greek Power
Join Date: Jul 2003
Location: Greece
Posts: 439
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by Ericok
It is plain physics but you're confusing energy with power. A flywheel is an energy storage device, it doesn't create, absorb or provide power. If you had NO flywheel, the horsepower delivered by the engine to the rear wheels at a given RPM would be the same (minus the frictional losses in the drivetrain and assuming you could keep the engine running). The improvement comes from allowing the engine to spin up quicker (which the lighter flywheel allows) which translates to HP being available earlier. In the end, the maximum horsepower (heavy flywheel, light flywheel or no flywheel) remains the same.
Reducing flywheel weight just re-shuffles the existing horsepower throughout the RPM range. If you really think that reducing flywheel weight increases RWP, then you should concentrate on reducing the weight of the wheels, tires, brakes and other rotating machinery in the driveline. Those items weigh an order of magnitude more than a flywheel.
Reducing flywheel weight just re-shuffles the existing horsepower throughout the RPM range. If you really think that reducing flywheel weight increases RWP, then you should concentrate on reducing the weight of the wheels, tires, brakes and other rotating machinery in the driveline. Those items weigh an order of magnitude more than a flywheel.
I'm not discussing whether the flywheel moves the powerband up or down, or relocates the point of maximum output. I am merely pointing out that reducing the mass of the flywheel increases the net amount of force with goes "through" the flywheel and finally spins the wheels (which is measured as WHP).
I had done a very generic calculation as to how much power is "freed up" by reducing the mass of a flywheel by a certain percentage, but it was done in Greek and cannot translate right now. I did this because I didn't want to take the assumptions of ACT or MazdaSpeed as granted. The result (my result) was that for every Kg of mass shaved off, about 0,5% of WHP is gained (actually it was 0,5% of wheel torque that is gained).
05-14-2006, 02:51 PM
#29
Registered
iTrader: (1)
Join Date: May 2003
Location: PA
Posts: 3,754
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by Ericok
It is plain physics but you're confusing energy with power. A flywheel is an energy storage device, it doesn't create, absorb or provide power.
The flywheel is connected to the engine - which varies in speed.
When the flywheel varies in speed, its stored energy changes. The change in energy over time is POWER.
When the engine spins up, the flywheel spins up increasing its energy, and the power that it takes to increase the flywheel energy is power that could be going to the rear wheels but is not. The faster the flywheel changes speed the more power it consumes - therefore the most gains from a lighter flywheel will be in first gear, and diminishing in every gear after that.
05-14-2006, 03:49 PM
#30
The Professor
Originally Posted by Ericok
It is plain physics but you're confusing energy with power. A flywheel is an energy storage device, it doesn't create, absorb or provide power. If you had NO flywheel, the horsepower delivered by the engine to the rear wheels at a given RPM would be the same (minus the frictional losses in the drivetrain and assuming you could keep the engine running). The improvement comes from allowing the engine to spin up quicker (which the lighter flywheel allows) which translates to HP being available earlier. In the end, the maximum horsepower (heavy flywheel, light flywheel or no flywheel) remains the same.
Reducing flywheel weight just re-shuffles the existing horsepower throughout the RPM range. If you really think that reducing flywheel weight increases RWP, then you should concentrate on reducing the weight of the wheels, tires, brakes and other rotating machinery in the driveline. Those items weigh an order of magnitude more than a flywheel.
Reducing flywheel weight just re-shuffles the existing horsepower throughout the RPM range. If you really think that reducing flywheel weight increases RWP, then you should concentrate on reducing the weight of the wheels, tires, brakes and other rotating machinery in the driveline. Those items weigh an order of magnitude more than a flywheel.
After reading the previous posts I'm beginning to see where you're coming from.
You think of the flywheel solely as a storage medium for potential energy.
Basically in your world you think that the engine can spin up the flywheel, energy goes completey into the flywheel and then can be transfered completely into the driveshaft upon engagement of the clutch.
It does store energy for the engine, it's sole purpose is to make it easier for humans to shift gears by keeping the momentum of the engine constant. But it saps energy doing it!
To put it simply, having mass at any distance from the center of any rotating object is going to need energy to spin.
Remember the good old days of the merry-go-round?
Now it was easy to spin the merry-go-round with no-one on it, you could make it go around really fast(giving it 100% of your energy), but it stopped spinning rather quickly.
-Because you had enough energy to perform the work required, factor in the amount of time it took you to get it spinning and we can calculate your horsepower!
Now when all your friends were on it, it was so hard to get spinning(giving it 100% of your energy) that you needed a grown-up to help you and even then it wouldn't spin that fast, but once it got spinning it seemed to go on forever.
-Because it was too hard/impossible for you to spin the merry-go-round you did not have the energy to perform the work required!
Now look at the speeds! the light merry-go-round went fast for the same amount of energy as the heavy merry-go-round needed just to get it started.
This is exactly what a flywheel is, its purpose IS to store energy, but what you neglect completely is the quantity of Impulse. Impulse is the amount of energy required to change the inertia of something.
Yes, changing the inertia of something does require energy! This is why it was harder to spin the merry-go-round with people on it!
Com'on dude I was a physics tutor.
05-14-2006, 06:51 PM
#31
Rotary Wanker
Just for argument's sake.... Don't you think that Mazda, who is DESPERATE to rate this engine's horsepower higher than it is, wouldn't have put in a lighter flywheel from the factory just to get the higher horsepower rating? They don't because they know flywheel weight doesn't make any difference in HP.
Don't get me wrong, there are plenty of good reasons for a lighter flywheel from an engine response standpoint. You can deliver what HP you've got faster and earlier. Because of that you can end up with improved quarter-mile or lap times. But, in the end, you've still got the same HP you started with - just delivered differently.
Don't get me wrong, there are plenty of good reasons for a lighter flywheel from an engine response standpoint. You can deliver what HP you've got faster and earlier. Because of that you can end up with improved quarter-mile or lap times. But, in the end, you've still got the same HP you started with - just delivered differently.
05-14-2006, 11:24 PM
#33
Registered User
Join Date: Apr 2006
Posts: 14
Likes: 0
Received 0 Likes
on
0 Posts
lightweight flywheel costs more for mazda to make and they dont care about any mods that only increase whp bc they advertise bhp. 238 bhp sounds better than an estimated 210 whp with a lightweight flywheel
05-15-2006, 12:40 AM
#34
Originally Posted by Charles R. Hill
That's what we have been saying all along; that a lighter flywheel makes itself less of a parasitic loss on the drivetrain, which results in more power left for the motivation of the vehicle. It has also been noted here that flywheel weights are a consideration made for the sake of driveability, not power numbers. If you look at the typical RX-8 owner, or potential owner, you'll see that they are not usually interested in a vehicle that will win races off the showroom floor. They are usually interested in a well-balanced vehicle that looks good and will carry more than two people. The RX-8 has been designed and executed very effectively for the demographic which it was/is intended to attract. That's the reason Mazda selected the flywheel weight they have; so more people of a wider variety can drive the car comfortably.
One thing I would ask others to consider is exactly how chassis dynos calculate the whp of a given vehicle. They do it by calculating the acceleration rate of a pair of wheels with a known mass and extrapolate h.p. numbers first. They then calculate torque using the formula stated earlier. The important thing is that the dyno wheels function the same way an engine flywheel does. If the dyno wheels were made lighter but the dyno software wasn't made aware of the change, it would calculate higher whp/wtq due to a quicker rate of acceleration.
The point made about the perceived effects of light flys and transmission gearing is why we try to use a transmission gear ratio as close to 1:1 as available. This removes the transmission as much as possible from skewing dyno numbers. If we could we would also use a final drive ratio of 1:1 to come as close to engine h.p. as was possible.
Isn't it enough just to say that, for performance purposes, a lighter flywheel is a benefit and then each of us report on the particular flywheel we have chosen to use and our experiences with them?
CRH
One thing I would ask others to consider is exactly how chassis dynos calculate the whp of a given vehicle. They do it by calculating the acceleration rate of a pair of wheels with a known mass and extrapolate h.p. numbers first. They then calculate torque using the formula stated earlier. The important thing is that the dyno wheels function the same way an engine flywheel does. If the dyno wheels were made lighter but the dyno software wasn't made aware of the change, it would calculate higher whp/wtq due to a quicker rate of acceleration.
The point made about the perceived effects of light flys and transmission gearing is why we try to use a transmission gear ratio as close to 1:1 as available. This removes the transmission as much as possible from skewing dyno numbers. If we could we would also use a final drive ratio of 1:1 to come as close to engine h.p. as was possible.
Isn't it enough just to say that, for performance purposes, a lighter flywheel is a benefit and then each of us report on the particular flywheel we have chosen to use and our experiences with them?
CRH
i will drive you and your car to tampa... you pay for gas...
yes i can fly to detroit for free.... we need you here..
beers
05-15-2006, 12:50 AM
#35
Registered
Originally Posted by Charles R. Hill
Regardless of what one's mathematic calculations may indicate or their understanding of physics may cause them to believe, the bottom line is that reducing flywheel weight to the lowest tolerable by the driver ends up making a more efficient drivetrain. If all a lighter fly does is cause the engine to rev up quicker, what physical phemonenon is it that allows the engine to rev up quicker? If the engine's ability to rev up quicker is the only observable outcome of a lighter flywheel does that mean that the engine will pass through it's powerband quicker also? If so, what do we do then? I can tell you from personal experience that switching to SR's 9.75# fly did not affect the driveability to the degree that some around here tend to speculate and that the acceleration was enhanced to the extent of shaving .3s off of my 1/4 mile time in both N/A and nitrous modes. At my current power/weight ratio that equates an extra 15 rwhp. For those who are interested the light fly is one of the most effective mods we have available to us, especially for the cost.
CRH
CRH
On the 13B nonturbo engines, you could get very large gains from a new exhaust. They were gains not possible with the Renesis. We're talking on order of 30+ hp from an exhaust alone. The 2 largest gains you could do to a nonturbo RX-7 was the exhaust and a flywheel. Everything else was less important. The acceleration gains were on par with that of streetporting the engine. That's right, a good flywheel could add the acceleration capabilities of a ported engine with the stock flywheel! I laugh at those that say a flywheel makes no difference in power to the ground. They need to actually drive one instead of speculate as to how something works that they have no experience with.
05-15-2006, 06:54 AM
#36
Registered
iTrader: (1)
Join Date: May 2003
Location: PA
Posts: 3,754
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by Ericok
Just for argument's sake.... Don't you think that Mazda, who is DESPERATE to rate this engine's horsepower higher than it is, wouldn't have put in a lighter flywheel from the factory just to get the higher horsepower rating? They don't because they know flywheel weight doesn't make any difference in HP.
Judgeing by the amount of people complaining of squealing brake pads on this forum from the braking system that produces the shortest distance of any japanese car, they were probably right in using a big ol driver friendly flywheel.
Thread
Thread Starter
Forum
Replies
Last Post
