light flywheel, or not light flywheel?
Discussion
I have an upgraded n54 335i that at the moment is quite rapid, I have recently posted a few problems and advice posts on here regarding this car which have now been sorted, But with my new grip and extra power and torque the car has I noticed that the clutch may be slipping a bit.
It has a jb4 box that I inherited with the car that I'm not too keen on however the map 5 setting remaps the car to allow for upgrades and I think now that its touching 86k miles with probably getting on for 400bhp plus in fact the clutch is struggling, so when I come to replace it (obviously with an upgraded one if needed??), do I go for a light weight fly wheel, while they are at it? what's the pros and cons please? I seen a car restoration programme where the mechanic changed to a light fly wheel on a Caterham and demonstrated how it benefits using 2 drills with a standard wheel and light one attached to each, the light one sped up quicker but slowed down quicker whereby he said could be a problem if you loose revs too quickly. so could this be an issue with general driving? This is my every day driver so need the usual creature comforts to a point but like the excitement of quick acceleration, so opinions please...... Thanks
It has a jb4 box that I inherited with the car that I'm not too keen on however the map 5 setting remaps the car to allow for upgrades and I think now that its touching 86k miles with probably getting on for 400bhp plus in fact the clutch is struggling, so when I come to replace it (obviously with an upgraded one if needed??), do I go for a light weight fly wheel, while they are at it? what's the pros and cons please? I seen a car restoration programme where the mechanic changed to a light fly wheel on a Caterham and demonstrated how it benefits using 2 drills with a standard wheel and light one attached to each, the light one sped up quicker but slowed down quicker whereby he said could be a problem if you loose revs too quickly. so could this be an issue with general driving? This is my every day driver so need the usual creature comforts to a point but like the excitement of quick acceleration, so opinions please...... Thanks
Lightweight flywheel pro's and con's.
Contrary to popular belief, a lightweight flywheel does not give the engine any more power. What it does do is reduce the rotating mass of the engine, enabling the power output to be transmitted more to the output shaft via the clutch to the transmission, than being used to accelerate the rotating mass.
It therefore TRANSMITS more power to the wheels DURING ACCELERATION only. At any given fixed engine speed, the power transmission is the same.
Therefore the benefit of the lighter flywheel is to increase power to the rear wheels during acceleration.
This can be quite a substantial amount too, with a BMW M5 transmitting around 40bhp more in first gear acceleration with a lightweight aluminium flywheel over the monstrous cast iron dual mass offering from BMW.
As the engine rpm drops faster, then gearshifts can be carried out much faster, both up and down the ratios.
This is essentially the pro's of a lightweight flywheel.
There are some con's to consider.
The heavy flywheel smooths the engine pulses, so on an engine with less than 4 cylinders, this can cause harshness on idle. Any loss in flywheel mass will also give the impression of a torque reduction when engaging the clutch and pulling away because the energy stored in the rotation flywheel is reduced, usually requiring slightly higher engine rpm's to pull away.
The more cylinders you have, the smoother the pulses are anyway and on anything from 6 cylinders or more, there should be no noticeable harshness, although the revs will still be needed when pulling away.
The other main con with a lighter flywheel is that whilst the engine revs up more freely, the revs also die faster and this can be a problem when the engine uses electronic idle speed control, because the electronics cannot keep up with the engine, and in extreme cases, the engine will stall.
To make a lightweight flywheel worthwhile, it needs to be much lighter than the stock unit, by around 50% and in my opinion, this means either an alloy unit or an extremely lightened steel unit, usually with a smaller diameter heavy duty clutch, or even a multiplate clutch to further reduce the rotating mass of the clutch too.
Hope that helps.
Contrary to popular belief, a lightweight flywheel does not give the engine any more power. What it does do is reduce the rotating mass of the engine, enabling the power output to be transmitted more to the output shaft via the clutch to the transmission, than being used to accelerate the rotating mass.
It therefore TRANSMITS more power to the wheels DURING ACCELERATION only. At any given fixed engine speed, the power transmission is the same.
Therefore the benefit of the lighter flywheel is to increase power to the rear wheels during acceleration.
This can be quite a substantial amount too, with a BMW M5 transmitting around 40bhp more in first gear acceleration with a lightweight aluminium flywheel over the monstrous cast iron dual mass offering from BMW.
As the engine rpm drops faster, then gearshifts can be carried out much faster, both up and down the ratios.
This is essentially the pro's of a lightweight flywheel.
There are some con's to consider.
The heavy flywheel smooths the engine pulses, so on an engine with less than 4 cylinders, this can cause harshness on idle. Any loss in flywheel mass will also give the impression of a torque reduction when engaging the clutch and pulling away because the energy stored in the rotation flywheel is reduced, usually requiring slightly higher engine rpm's to pull away.
The more cylinders you have, the smoother the pulses are anyway and on anything from 6 cylinders or more, there should be no noticeable harshness, although the revs will still be needed when pulling away.
The other main con with a lighter flywheel is that whilst the engine revs up more freely, the revs also die faster and this can be a problem when the engine uses electronic idle speed control, because the electronics cannot keep up with the engine, and in extreme cases, the engine will stall.
To make a lightweight flywheel worthwhile, it needs to be much lighter than the stock unit, by around 50% and in my opinion, this means either an alloy unit or an extremely lightened steel unit, usually with a smaller diameter heavy duty clutch, or even a multiplate clutch to further reduce the rotating mass of the clutch too.
Hope that helps.
brilliant cheers, I did have a rough idea as to how they worked, being lighter - spinning up quicker and dropping quicker, but in the instance of a 2007 335i, would it be user unfriendly for day to day use? Bare in mind the car is modified and running around 400bhp, interesting bit of info though, thank you
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