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Discussion Starter #1
Some1 settle this argument does a lighter flywheel give you more power and torque or just power......

I'm sure it's just power.......and you lose some torque.......as GT (the game shows a it as a possable downside re:torque)

also torque is pulling ie: caravans or hill's......


Thanks
 

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Iwoulda thought both, but then again, its a complex equation.... you lose momentum on the rpms so it will be more free revving, but less momentum i think means less torque....


Now I am confused
 

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Dandy Highwayman
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wheeheey I'm a google genius;

edit - just to be clear I nicked this from
http://www.minimania.com/
- looks left n right - you aint seen me right.

How does this affect performance? Not as many folk believe, that’s for sure. For a start, lightweight flywheel/clutch assemblies don’t necessarily give rough running at idle, particularly where a performance cam is used. Nor do they make the engine produce MORE power. BUT they do make a difference to the ACCELERATIVE performance of the car - and that is what we’re most interested in most of the time! Basically, the engine sees the car as a weight to move, via the gearbox.

The combustion pressures created by your common or garden suck-push-bang-blow engine have to accelerate not only the mass of the car as a whole, but the mass of the engine internals too. However, the engine can only accelerate the car at a certain rate with what power is left over after the engine internals have consumed their share. The lighter the rotating and reciprocating parts are made the less power is consumed by them, leaving more to actually accelerate the car. I’m going to ignore the reciprocating stuff here (rods, pistons, etc.), as it is more complicated to determine their effects.

To over simplify things, the gearbox is no more than a complex lever. Taking off in first gear, the engine doesn’t see the total mass of the car. It really sees the total mass divided by the total gear ratio. To illustrate, a Mini is roughly 1400lb without driver (we’ll do this by remote control - I don’t want any hate mail by different ‘weight’ factions). Take a first gear ratio from a standard gearbox of 3.33, and multiply by final drive of said gearbox of 3.44. The over all ratio is 11.45. Now, the engine actually sees the weight of the car (1400lb) divided by the overall ratio in first gear (11.45) - so that’s only 122-odd pounds. BUT it also sees the extra weight of the flywheel/clutch assembly and a few other drive train components - typically around 40lb. It now sees a total of around 162lb. Lightening the flywheel/clutch assembly by 10lb means the engine sees 6% less mass to accelerate. A considerable difference compared to the overall mass!! Of course this will deteriorate as you go up through the gears. This neatly illustrates the fact that no amount of lightening will make an iota of difference to the top speed. It can also be seen that where more modified, higher-revving engines are used with lower ratios to achieve maximum performance, the greater effect the lightening has. Thus the faster the car will accelerate.

The formula to assess the effect of lightening the flywheel per pound in conjunction with various gear ratios, final drive ratios, and wheel/tyre sizes is;

(0.5 x n2 x r2 + R2 ) / R2

n = Total gear ratio (gear ratio x final drive ratio)
r = Radius of gyration
R = Radius of wheel/tyre used.

Calculating the radius of gyration of other components, such as the pressure plate, will allow further ‘button punching’ for further assessment.

Incidentally, balancing the crank and flywheel assembly will not improve the rpm capability of the engine at all. Not unless you have some particularly bothersome vibration. Neither will it give any power increases. ALL it will do in reality is give a smoother running engine. That’s it. So if the budget is tight for a road engine rebuild, your money may well be better spent elsewhere, particularly where the components used are as they were fitted at the factory from the same engine.
 

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Dandy Highwayman
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i think it says its not really about power or torque - its about how much weight your engine is having to spin up to speed

its more akin to lightening the chassis only thanks to the gearing in low gears the effect is multiplied so that 1kg off the flywheel is like say 10kg wieght saved in the chassis.

so just like making your chassis lighter it doesnt effect power or torque but it does make you accelerate better.
 

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So, as alex says, it frees up the engine somewhat.
I guess that would equate to an increase at the wheels as there would be less of a drop on the way.

Although, as BHP is measured at wheels or fly, and its a lighter fly, maybe there is squat all difference after all.

I personally reckon you would see a small improvement in acceleration times, but probably a marginal increase at the wheel.

In terms of bang for buck, its gotta be way down the list of things, next to paying for girlfriend plastic surgery!
 

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Dandy Highwayman
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yeah, last of the power gain tweeks but first of the weight saving tweeks

fro an example on a scooby (phaa spits in dsigust) For your 15 lb reduction example, in 1st gear the car should accelerate as if you've lightened the car by over 250 lbs. (edit sorry stated that as fact - when I just nick it from the nasioc forums - but it seems inline with the mathematical stuff i posted earlier)

compare that to sarky's post about taking hicas out (50lbs i think)
 

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Discussion Starter #9
thanks guys but as I said I'm not going down this road just trying to settle an argument....any 1 else with a veiw..
 

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basically, what has already been said by AlexJ seemed correct. I got bored half way through!

The power of the engine is not increase as the combustion remains the same. However, have a lighter flywheel reduces the loss of drive to the wheels, in the same way a carbon drive shaft does. This equates to more power reaching the wheels, hence faster acceleration.

If you put a car on the rollers, before and after lightened flywheel, engine power and torque would be identical (in a perfect environment), but the power and torque at the wheels would be slighty (and I think slightly is the best way to describe it) increased with the lightened flywheel.
 

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M's Factory
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less weight on turning forces means faster spin up time. IT can be confused with torque as torque essentially gets you going, and BHP keeps your car at the desired speed.

The lighter you can get the drive train the better on all the turning parts would equate to a faster accelerating engine.

Points for Martin, he wins the bullys special prise, shame you dont have a tow bar to take your caravan with you mate :)
 

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Discussion Starter #12
"An ultra light flywheel for racing use both rises and fall of engine speed is sudden accelration and decelraton is both improved,but a side effect that with narrow torque range engine a car tends to lose speed easy when the road rises." quotedfrom tech info on GT3
 

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NismoUk, that is accurate. It loses speed on inclines because of a loss in momentum on the crank and drive train
 

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Nismo...
Increase the ration of the V system Hub..This causes the drive chain to get warm and will increase the torque ration. With this in mind the hills should become no problem.

Jasper
 

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I would of thought that if you are putting more power to the wheels due to your lighter flywheel then it doesn't matter if you are going uphill,downhill or flat ?

Also isn't BHP a function of torque, i.e torque X revs divided by a constant (that I can't remember :) ).
In which case a lighter flywheel should should allow your engine to produce more torque at the wheels which in turn produces more BHP at the wheels as you lose less turning the heavy flywheel.

Another factor with a light flywheel is lag and how it affects this.
I find my car feels better off boost with the light flywheel as it is more lively and revvy. I reckon that due to the slightly decreased load on the engine it also causes the turbo to spin up a little later in the lower gears.

Any thoughts on this ?

Jez
 

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Dandy Highwayman
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another thing is that you loose the benifit of the initeria that is stored in a spinning heavy fly wheel when you do a 3500 rpm clutch drop that normally launches you, so the car may feel a bit slower initially

that said it sounds like most people who have a lightened flywheel can *feel* an improvement in performance even if its hard to make this to show up on a dyno!
 
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