# Aluminum Flywheel?



## Coley (Jul 26, 2007)

I don't believe it is worth the expense. It would let you accelerate a little quicker, but not enough to make it pay.


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## Dalardan (Jul 4, 2008)

The flywheel purpose is to keep motor spinning between exposions, therefore smoothing the torque (Instead of a high frequency pulsed torque, the output of the ICE motor is averaged). This, for example, would allow a monocylinder to keep enough energy between explosions to continue spinning.

Also, the rotating inertia of the flywheel opposes itself to changes in motor RPM. Yes, it opposes itself to car acceleration, but also it gives a torque boost while removing your feet from the clutch. A heavier flywheel will make your ride more comfortable, smoothing the jerky ride of a street driven racecar ... . A lighter one will make your ride more nervous, but it will also be harder to let go the clutch (you'll need your motor to turn faster before "declutching"), especially when starting to move while climbing a cliff. This will make your car less easy to drive. If you can live with a more jerky ride and a more "capricious" ride, then go for it if you've got money. Personnally, I wouldn't ligthen it unless you can drive always full throttle.

On the other hand, on an EV, the torque isn't pulsed by the action of the cylinders, thus you don't need a flywheel at all . Unless your ride is so jerky that you want to make it less responsive....

Dalardan


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## DavidDymaxion (Dec 1, 2008)

If the pressure plate is alot smaller than the flywheel, you can have a machinist cut down the flywheel much cheaper than buying a racing flywheel.

A typical car is geared roughly 12:1 in 1st, 9:1 in 2nd, 6:1 in 3rd, 4:1 in 4th, and 3:1 in 5th.

During acceleration, every pound saved on the flywheel is 1/2*gear ratio, like 6 lbs saved in 1st gear, 4.5 lbs saved in 2nd gear, 3 lbs saved in 3rd gear, etc.

So if you did nothing but stop and go in 1st gear (no regen), its like saving (20*6*1/2+20*1/2) (you only accelerate 1/2 the time, and brake 1/2 the time), equivalent to saving 70 lbs on the car for range. For a 3000 lb car, you'll get 2% more range. The worst case, steady highway cruising (1/2 your energy to rolling resistance and 1/2 to aero drag), you only get 0.6% more range. So it boils down to this: Is $350 worth 1% more range?

Now for racing, it's another story entirely. Shaving 0.1 or 0.2 seconds off your ET well could be worth $350. Also, some racing associations don't allow cast flywheels.

In any case, you shouldn't give up on lightening the car. Remove extra junk, or you might be able to get lightweight wheels cheap, or maybe you can get a lightweight hood cheap.


BWH said:


> Is the speed/range gain worth the extra expense of getting an aluminum racing flywheel in a (mostly) street driven vehicle?
> 
> Searching back through the forum I found someone that said that taking 15lbs. off the flywheel was like taking 50-200lbs. out of the car depending on the gear.
> 
> The cheapest aluminum flywheel I could find was $350, but it would save a bit over 20lbs. compared to the OEM Saturn flywheel weight. 8lbs. vs. 28lbs. before removing the ring gear.


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## BWH (Sep 26, 2008)

Thank you all for the input. While I would love to get rid of the flywheel completely I am keeping the clutch for safety reasons.

I think I'll go with cutting down the flywheel I have now. I can always go back and play around with it later on. That's the fun part of DIY.


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## dtbaker (Jan 5, 2008)

just be aware that if you change it at all, you'll need to rebalance.... Sometimes the starter gear ring is basically just shrunk on, and I have seen pictures of guys drilling one or two tooth 'valley', and the cracking the starting ring off with a chisel. but, you'd probably still want to re-balance.


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## Caps18 (Jun 8, 2008)

Is anyone using an aluminum flywheel in their EV? Is the $320 cost a little too high compared to the benefits still? Is regen on the AC motor impacted at all if the flywheel is lighter? Is it easier on the motor to start from a stop in 2nd gear if it has 20lbs less to spin? Any difference when shifting gears at speed?


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## dougingraham (Jul 26, 2011)

Caps18 said:


> Is anyone using an aluminum flywheel in their EV? Is the $320 cost a little too high compared to the benefits still? Is regen on the AC motor impacted at all if the flywheel is lighter? Is it easier on the motor to start from a stop in 2nd gear if it has 20lbs less to spin? Any difference when shifting gears at speed?


I am using one. I can't answer the benefits vs cost because the stock flywheel on the 12A Wankel motor is counterbalanced so not usable without a lot of rework. I had to replace the flywheel so I got an aluminum one. I can tell you that a lighter weight flywheel will improve acceleration which is why racers use them. Less mass to spin up. Shifts will be smoother with a lighter flywheel because the speeds can be more easily be matched. Regen is better with a lightweight flywheel because less energy is wasted on acceleration and although you would get more back with a heavy flywheel it costs you more overall. The only downside is that there is less energy stored in the flywheel so when you redline the motor in neutral and drop the clutch you don't get nearly so impressive of tire spin or flying parts when something breaks (<evil-grin>.) The only reason for a heavy flywheel in an ICE is so you have enough stored energy to get moving without stalling the engine.

There are no downsides to having a lightweight flywheel in an EV. It is all good.


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## elevatorguy (Jul 26, 2007)

I have an 8 pound flywheel in my Mazda and like Doug I had to lose the counterweight for the rotary engine.
I can start easily in 2nd and can even use 3rd from a stop.
Look for a used one or cut down the stock piece. I picked mine up used at a great savings.


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## DavidDymaxion (Dec 1, 2008)

My EV has an aluminum flywheel. Best case: It is as if the car is 4% lighter in 1st gear while accelerating (less in higher gears), but only 0.4% lighter when going a steady speed. The $320 is better spent on another battery unless you are a racer looking for every fraction of a second.



Caps18 said:


> Is anyone using an aluminum flywheel in their EV? Is the $320 cost a little too high compared to the benefits still? Is regen on the AC motor impacted at all if the flywheel is lighter? Is it easier on the motor to start from a stop in 2nd gear if it has 20lbs less to spin? Any difference when shifting gears at speed?


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## Duncan (Dec 8, 2008)

You don't need or want a flywheel in an EV

if you are keeping the clutch you do need something for the pressure plate to act on

best thing to do is to take your existing flywheel put the pressure plate on it and get everything you don't need machined off

it will be better (lighter) and cheaper than an ally flywheel


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## onegreenev (May 18, 2012)

Take your existing flywheel and have it cut down to the size of your pressure plate and so you can still bolt it up to your pressure plate. As for keeping, Yes its good to keep it but you really won't be shifting much. Just put it into a gear and go. But you can disengage if needed. I usually shift so needed to keep the flywheel and clutch. Here is a picture of a cut down stock VW flywheel. It was cut but a small lip was retained to locate the flywheel when mounting. It is mandatory to rebalance your flywheel and pressure plate no matter what. Your motor will be much smoother if you do. If you use your stock pressure plate and flywheel you really don't have much to worry about on the street. Works just fine and the acceleration is quite brisk. The electric motor is so powerful and has so much torque it really just is not affected by the little larger sized flywheel. If an electric motor can pull a VW Ghia that is loaded with over a 1000 lbs of lead like it was not there, I know the stock flywheel is not going to be any issue. 

On the track its a whole different story. 


Pete


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## Caps18 (Jun 8, 2008)

There isn't much to cut down though. I will post a picture of what I have now, and there are only a few teeth all around it that could be grounded off.

It might not be much of an energy efficiency improvement, but it is one of those things that would probably bug me. I know there is a difference when pedaling my mountain bike compared to the triathlon bike with the weight of the wheels.


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## onegreenev (May 18, 2012)

Ya know, I would not worry about it. Its not that big of a deal to have a regular flywheel. The biggest deal you need to worry about is getting the whole assembly balanced. Balance it to like 6000 rpm or better. That way the whole assembly will run smooth and true with little to no vibration. If you were out racing then I'd figure a way to have the least in the system but even so a good racing clutch for racing is in my opinion imperative unless your only doing one speed. It gives the ability to take up a little shock as you launch. Same with your situation. Your motor produces quite a bit of torque and having a clutch will help reduce the shock load. 

You could have the teeth removed and some weight removed from the back side of the flywheel and reduce some weight but I would not obsess over that issue. Your driving a street car after all. Like I said in my previous post. The little extra weight even from rotational mass is nothing to the electric motors torque. Don't worry or fret. 

Pete


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## bwjunkie (Jul 31, 2013)

onegreenev said:


> The little extra weight even from rotational mass is nothing to the electric motors torque.


I agree. I was swayed on the rotational mass argument early on in my EV experience and I was an easy victim because my experience in the 2 wheel racing world, where carbon fiber rims are the "bomb" for this same reason. But a huge difference here, the flywheel isn't being moved on 3+ axis at once, the issue of the gyro effect is not really a concern. 

I currently have a clutchless system, and I very much look forward to the day that I have a clutch again.
-josh


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## DANNP (May 28, 2014)

I am new to the ev circle, however ice have been my life. I am going to ask a question that may or may not have been covered. Is the ice flywheel you have off of an internally balanced engine, or externally? Some vehicles have an externally balanced crank. Meaning the flywheel is weighted to balance the crank shaft at high rpm. It's my understanding that it takes the vibration out of the centrifugal mass. Similar to balancing your wheels. Now the harmonic balancer absorbs the resonating vibration out of a ice, produced by the fuel explosion. It may make no difference, but I would think if you are using a flywheel on an electric motor, it should be balanced neutrally on it's own.


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## Caps18 (Jun 8, 2008)

I was under the false impression that the stock flywheel weighed twice as much as it actually does. It would only save 10-12 lbs I bet by switching to aluminum. If I were building thousands of these cars from scratch, I would pick Al, but I think it will work fine as it is.


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