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Old 14th August 2006, 23:09   #1
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Default Flywheel Weight Reduction / Lightened Flywheels

Hi Guys..!!!

As far as my knowledge stretches reducing flywheel weight:
1.reduces the rotational intertia of the engine
2.faster in acceleration(straight line)
3.engine will rev up much faster

Now Gurus pls highlight all the cons of reducing flywheel weight reduction

My doubts
1.Does lightening of flywheel really improve the acceleration?? how much???

2.Is there a limit of reducing the flywheel weight???

3.Has anyone done this here ???


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Old 15th August 2006, 05:15   #2
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hey buddy im no guru out here im just trying to give my two bit's..well yes flywheel lightening does help to an extent tried and tested...i wouldn't call it a remarkable difference in performance but i would deifnately call it a noticeable one..also yes there is a certain limit to which a flywheel can or should be lightened..an extra light flywheel can also lead to power drop..as in the rpm will fall as quickly as it rises..and that again is of no use ..i think mahesh(shivaji park) should be able to help you out..also opt for electronic flywheel lightening..tc..cheers..happy revvin...!!
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Old 15th August 2006, 08:28   #3
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Quote:
Originally Posted by dragger
hey buddy im no guru out here im just trying to give my two bit's..well yes flywheel lightening does help to an extent tried and tested...i wouldn't call it a remarkable difference in performance but i would deifnately call it a noticeable one..also yes there is a certain limit to which a flywheel can or should be lightened..an extra light flywheel can also lead to power drop..as in the rpm will fall as quickly as it rises..and that again is of no use ..i think mahesh(shivaji park) should be able to help you out..also opt for electronic flywheel lightening..tc..cheers..happy revvin...!!
Agree with dragger, there is an improvement in performance when you use a light weight free-wheel although it is not a remarkable difference. I would put it this way. If you are want a fast car this is one of the things you must definitely do. These small improvements add up to your car's tranformation into a fast car.

But when you get this done, make sure your new or modded flywheel is weight-balanced. This is to make sure there is no wobble (similar to wheel-balancing). I am sure a good mechanic will know this already.
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Old 15th August 2006, 09:38   #4
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how about a drop in torque..can anybody highlight on this aspect..??
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Old 15th August 2006, 13:08   #5
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Lightweight Flywheel

Pros
1) A Turbo charged engine benefits the most beacause it reduces Turbo Lag by revving quicker due to lightweight.
2) A Slight improvement in mid range torque is noticed in an N.A engine cause the engine has not to overcome the heavy weight of stock flywheel.
3) Overall an increased in acceleration due to reduced weight of flywheel power is used to drive Wheels instead of flywheel.

Cons
1) For a street car drop in engine rpm quicker while changing gear, eg: say at 4000 rpm when you change gear from 2nd to 3rd, with stock heavy flywheel it holds around that rpm cause it stores that energy in rotation form hence gear shift is smoother, for a lightweight flywheel theres no energy stored & hence rpm drops of quickly so when you engage in 3rd the engine rpm is lower for that gear ratio & car running u will notice a jerk or thud sound when it engages, only solution is to rev the engine slightly so that vehicle speed & engine rpm are in harmony with gear shift.
2) An imbalance lightweight flywheel will be a nightmare for engine with undesirable results.
3) removing weight from wrong portion of stock flywheel will result in flywheel cracked & can damage block or engine components.
3) mostly new engines which are distributor less has Crankshaft position sensors & it reads from the teeth which are embeded in flywheel to determine TDC/BDC, if it is removed unknowingly to reduce weight your car will never start!

Putting Aftermarket billet alluminium flywheel which is lighter & stronger is recommended rather than shaving weight of stock flywheel, only if aftermarket option is not availabe then you can shave your stock flywheel & reduce its weight by 20-25% & balanced done up by a professional.
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Old 15th August 2006, 17:41   #6
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Ok, this is a very 'layman'-ish question, but is engine braking affected in any way when lightening the flywheel?
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Old 15th August 2006, 22:17   #7
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Quote:
Originally Posted by islero
Ok, this is a very 'layman'-ish question, but is engine braking affected in any way when lightening the flywheel?
Good question imo,

You should experience greater engine braking with a lighter flywheel as it will have less inertia (less mass = less inertia) and therefore will let the engine decelerate quicker.
This ofcourse is my deduction, and assuming that it is in-gear engine braking.

However, in the case of a quick downshift to decelerate, chances are that it will not decelerate as well as a heavier flywheel for that short period of time because there is less mass to be accelerated on the flywheel (absorb the energy), but on the other hand, the RPMs will have dropped faster during the (clutch disengaged part of the) shift than with a heavy flywheel, so it is a hard to come up with an accurate theoretical answer without knowing specifics.

cya
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Old 15th August 2006, 22:30   #8
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I think Engine Braking Should suffer.... though i don't know how correct my deduction is! Apart from that it will really hamper day to day commuting!
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Old 16th August 2006, 18:08   #9
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By reducing the inertia of the flywheel, you definetly improve the pick up and engine braking but by a small margin.

The side effects is that the engine vibration is increased. The engine goes through cyclic load changes through entire cycle (two revoultions for four stroke) which vaies a lot and is not good for the engine health. To understand this, try to run 2 mts with max speed and then another two mts walk and then again run 2 mts at max and so on. The flywheel takes the this kind of shock filters this cyclic load changes (something like filters fitted to rectifier cicuits in electrical equipments).
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Old 5th April 2007, 17:12   #10
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Default Lightened Fly-wheels

Hi All,

I'd like to discuss the (a) technical consequences and resulting (b) Merits and Demerits of doing this.

What I know is that a lightened flywheel will store less energy and lead to the engine being more free-revving .. what does this mean in English?

Specifically, - how will it impact daily driving? Has anybody on the forum replaced their OE flywheel with a lightened one?

I'm just setting stage for the experts to jump in - will try to share more of my queries as we go along ..

Regards,
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Old 5th April 2007, 17:39   #11
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@manveet - not much idea about the lightened fly wheel... but recently 1100D got a lightened fly wheel in his fiat 1100d. i am sure that it can be used for daily driving.
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Old 5th April 2007, 19:14   #12
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if you get a lighter flywheel you will have better throttle response but mostly in the mid to higher rpm range. you will lose a little bit of driveability in-town and car will lurch in higher gears if you try to "lug" it.

If the flywheel is made too light, it might shatter at high rpms and do nasty things which i dont want to talk about. But I am sure there are a lot of people who can do it right for the newer cars.
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Old 5th April 2007, 19:29   #13
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Our car engine makes the least torque at idle and low RPM, especially when cold (when there are more misfires.).... So when you release your clutch a little too fast, the engine torque is too small to overcome the inertia of the car, and it stalls. Thats where the flywheel comes to action ...the stored momentum of the flywheel augments the engine's torque allowing you to use a lower rpm starting-off.
So if you go for a lighter flywheel you'd need a higher idle speed, or constantly need to start-off at a higher rpm in order to raise the engine torque output enough to avoid stalling the engine.
As you ride at lower rpm in traffic, you are constantly changing between acceleration and deceleration. Engine torque levels are still fairly low at these speeds, so slack in the drive train needs to be smoothed-out with a flywheel. Otherwise, on-off throttle transitions have a jerky effect, giving a less comfortable ride.

At higher speeds a heavy flywheel slows the rate at which an engine rpm changes, so cracking the throttle open or closed results in a smoother transition in torque being applied to the drive train and tires. So I think with a light flywheel more careful throttle transitions would be needed .

I think getting a lighter flywheel is not advisable for city driving. But if you want to burn the track then you can go for it .Still you have to be careful when you are shedding some weight of the flywheel ,it should be just right
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Old 5th April 2007, 22:29   #14
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To add to what the others have expalined quite well.

Quote:
Originally Posted by manveet View Post
Hi All,

What I know is that a lightened flywheel will store less energy and lead to the engine being more free-revving .. what does this mean in English?
The purpose of the flywheel is to reduce the stress on the differential. Its of a particular weight so as to prevent the rpm to drop or rise very rapidly.

If the flywheel is lightened there is less weight on the crankshaft in turn helping the rpm to rise and fall easily. The lightened flywheel during gear change will drop the rpm rapidly and also accelerate quicker. Also it needs to be perfectly balanced, if it is lightened too much then it gets very difficult to drive the car.

Or if we put it like this a lightened flywheel stores less inertia but the lighter weight significantly improves engine response and acceleration. One should be able to cut couple of seconds(a big amount if you are on track but needs to be perfectly done) off with a lightened flywheel over a stock one.

For a stock car, if you want better acceleration or higher top end there are othe mods. Lightning a flywheel needs a lot of expertise.
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Old 6th April 2007, 03:10   #15
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Quote:
Originally Posted by Spitfire View Post
Lightning a flywheel needs a lot of expertise.
I thought it just needs a lathe, a calculator and a weighing scale. LOL just kidding.
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