Lightweight flywheels
Discussion
I know what the supposed benefits of a lightweight flywheel are, but I was wondering how tangible they are? My car is a Suzuki Cappuccino (660cc 12-valve turbo running an estimated 75hp at the flywheel, around 700kg kerb weight). The standard flywheel supposedly weighs in at around 8.1kg. I can get a lightweight one weighing 3.4kg.
Basically just want to know how much improvement I could expect in terms of power and throttle response. I don't know if it's an easy one to answer or not so any feedback would be great
Basically just want to know how much improvement I could expect in terms of power and throttle response. I don't know if it's an easy one to answer or not so any feedback would be great
i would think it would be an awful idea on that engine, it isn't reknowned for torque at best so losing a lot of weight off the flywheel would make it a handful in town, even though the car weighs as much as a bag of crisps.
Put it this way i used to have a very rapid midget, which went from a full race 1340cc to a turbo both of which with lightened internals and flywheel, and hot cam on the 1340, it was not overly pleasant to drive in town and my G/f at the time couldn't even get it up on to my driveway.
Put it this way i used to have a very rapid midget, which went from a full race 1340cc to a turbo both of which with lightened internals and flywheel, and hot cam on the 1340, it was not overly pleasant to drive in town and my G/f at the time couldn't even get it up on to my driveway.
Have a read of this :
www.pumaracing.co.uk/FLYWHEEL.htm
If you go too far - it can be dangereous as the flywheel cam break .. plus driving around town will become very very jerky.
www.pumaracing.co.uk/FLYWHEEL.htm
If you go too far - it can be dangereous as the flywheel cam break .. plus driving around town will become very very jerky.
Lightening the flywheel makes no difference to engine power, though it will improve throttle response and therefore acceleration.
However, flywheel mass is important to help smooth running at low revs and tickover. No problem on race cars, but on a road car too light a flywheel (and I think 3.4kg is probably too light) gives a very lumpy tickover that can make the whole car vibrate.
These days reducing weight by using aluminium flywheels is one expensive option. Traditional way was to have metal machined off original steel flywheel, but taking too much off can result in a weak flywheel that disintegrates at high revs.
Possibly worth having the flywheel lightened (by someone who knows what they're doing) if you've already got the engine out, otherwise the tiny gain in accleration you'll get is more trouble than it's worth.
However, flywheel mass is important to help smooth running at low revs and tickover. No problem on race cars, but on a road car too light a flywheel (and I think 3.4kg is probably too light) gives a very lumpy tickover that can make the whole car vibrate.
These days reducing weight by using aluminium flywheels is one expensive option. Traditional way was to have metal machined off original steel flywheel, but taking too much off can result in a weak flywheel that disintegrates at high revs.
Possibly worth having the flywheel lightened (by someone who knows what they're doing) if you've already got the engine out, otherwise the tiny gain in accleration you'll get is more trouble than it's worth.
The ultimate power the engine produces at a fixed rpm will not increase. With lighter engine internals less power is used to accelerate the engine componants so more is left over to accelerate the car. Also as the the engine operates through a gearbox the effect is most pronounced in lower gears where the effect is multiplied by the gear ratio.
Thinking about the overall mass of the internals of your 660cc engine I don't think 3.4Kg is too light.
Steve
Thinking about the overall mass of the internals of your 660cc engine I don't think 3.4Kg is too light.
Steve
no technical details here, just a comparison:
my vauxhall astra, 2.0 16v has 160bhp with a lightweight flywheel and weighs about 850kg
my mates (ex-)corsa, 2.0 16v has 181bhp with standard flywheel and weighs about the same (possibly 50kg less?).
at santa pod his best is a 14.2sec 1/4 and i mine is a 14.8s 1/4.
however, the first 1/3 of the mile i leave him for dead simply because i can launch so much quicker than him, he then uses his sheer power advantage to catch and pass me (posting about a 6mph higher top speed to boot), but for that initial launch i am triumphant!
not very scientific i know, but it shows a difference, whether it would on your car i'm uncertain!
on the downside, my car is a bugger to drive in traffic, especially when cold.
this wasn't a very helpful post was it?
my vauxhall astra, 2.0 16v has 160bhp with a lightweight flywheel and weighs about 850kg
my mates (ex-)corsa, 2.0 16v has 181bhp with standard flywheel and weighs about the same (possibly 50kg less?).
at santa pod his best is a 14.2sec 1/4 and i mine is a 14.8s 1/4.
however, the first 1/3 of the mile i leave him for dead simply because i can launch so much quicker than him, he then uses his sheer power advantage to catch and pass me (posting about a 6mph higher top speed to boot), but for that initial launch i am triumphant!
not very scientific i know, but it shows a difference, whether it would on your car i'm uncertain!
on the downside, my car is a bugger to drive in traffic, especially when cold.
this wasn't a very helpful post was it?
littlegearl said:
no technical details here, just a comparison:
my vauxhall astra, 2.0 16v has 160bhp with a lightweight flywheel and weighs about 850kg
my mates (ex-)corsa, 2.0 16v has 181bhp with standard flywheel and weighs about the same (possibly 50kg less?).
at santa pod his best is a 14.2sec 1/4 and i mine is a 14.8s 1/4.
however, the first 1/3 of the mile i leave him for dead simply because i can launch so much quicker than him, he then uses his sheer power advantage to catch and pass me (posting about a 6mph higher top speed to boot), but for that initial launch i am triumphant!
not very scientific i know, but it shows a difference, whether it would on your car i'm uncertain!
on the downside, my car is a bugger to drive in traffic, especially when cold.
this wasn't a very helpful post was it?
my vauxhall astra, 2.0 16v has 160bhp with a lightweight flywheel and weighs about 850kg
my mates (ex-)corsa, 2.0 16v has 181bhp with standard flywheel and weighs about the same (possibly 50kg less?).
at santa pod his best is a 14.2sec 1/4 and i mine is a 14.8s 1/4.
however, the first 1/3 of the mile i leave him for dead simply because i can launch so much quicker than him, he then uses his sheer power advantage to catch and pass me (posting about a 6mph higher top speed to boot), but for that initial launch i am triumphant!
not very scientific i know, but it shows a difference, whether it would on your car i'm uncertain!
on the downside, my car is a bugger to drive in traffic, especially when cold.
this wasn't a very helpful post was it?
Not massively
Only messing, any advice/experience is helpful. rev-erend's post has given me the best insight. I think I could spend my money much better elsewhere for the timebeing
grahambell said:
Lightening the flywheel makes no difference to engine power, though it will improve throttle response and therefore acceleration.
Nothing to do with the wooly and undefinable quality that is "throttle response". Lightening the flywheel gives you more power at the wheels under acceleration, because the flywheel isn't absorbing it.
My brothers mini has an ultra-light steel flywheel and although the idle is certainly lumpy (Kent 286 Scatter cam) it's quite drivable even in traffic.
Boosted LS1 said:
A heavy flywheel dampens the engine pulses plus it stores energy which is very useful when you're cruising on the M1 at 3k rpm's. Just dab the throttle and off you go. It would be a nightmare with a lightweight flywheel.
Boosted.
Boosted.
If I was cruising at 3000rpm in my car, I wouldn't even be at 50mph in 5th
MR2Mike said:
grahambell said:
Lightening the flywheel makes no difference to engine power, though it will improve throttle response and therefore acceleration.
Nothing to do with the wooly and undefinable quality that is "throttle response". Lightening the flywheel gives you more power at the wheels under acceleration, because the flywheel isn't absorbing it.
A lighter flywheel reduces the mass and therefore the inertia of the moving engine components. Consequently when you press the accelerator pedal the engine revs up more quickly, and when you lift off the accelerator pedal the revs drop off more quickly. I think most people would class that as increased throttle response.
grahambell said:
MR2Mike said:
grahambell said:
Lightening the flywheel makes no difference to engine power, though it will improve throttle response and therefore acceleration.
Nothing to do with the wooly and undefinable quality that is "throttle response". Lightening the flywheel gives you more power at the wheels under acceleration, because the flywheel isn't absorbing it.
A lighter flywheel reduces the mass and therefore the inertia of the moving engine components. Consequently when you press the accelerator pedal the engine revs up more quickly, and when you lift off the accelerator pedal the revs drop off more quickly. I think most people would class that as increased throttle response.
I would
grahambell said:
MR2Mike said:
grahambell said:
Lightening the flywheel makes no difference to engine power, though it will improve throttle response and therefore acceleration.
Nothing to do with the wooly and undefinable quality that is "throttle response". Lightening the flywheel gives you more power at the wheels under acceleration, because the flywheel isn't absorbing it.
A lighter flywheel reduces the mass and therefore the inertia of the moving engine components. Consequently when you press the accelerator pedal the engine revs up more quickly, and when you lift off the accelerator pedal the revs drop off more quickly. I think most people would class that as increased throttle response.
So to get the benefit of a lightened flywheel, you'd need to rev the nuts off it, otherwise the weight (or lack of) the flywheel is not enough to keep the gearbox and engine spun up.
I've toyed with the idea for making my kitcar a bit quicker. Would it be correct in thinking that if the flywheel - at it's standard weight - is fine for a Renault 21, one half it's weight would be ok for a kitcar weighing around little more than 1/2 a ton. Drivability wouldn't be an issue since I don't use it as a daily runner.
Any advice on modifying a 2 Litre Renault 21 engine/gearbox would be much appreciated.
To the original poster, you should consider the above advice. I used to have a 205 MI16 running fast road everything and twin 45's. It was certainly a lot of fun when driving 80% of it's potential but a pain around town. My advice would be to get yourself a kitcar that you won't need to run on a daily basis
its like this if you lighten the flywheel to get it to climb an hill you will have to drop a gear and spin the motor up,otherwise it will bog out(low inertia)the engine will feel like its lacking torque under load,but when you spin it up it will rev very freely,you can strike just the right compromise ask a good engine builder for advice,yes i have built many engine with lightened flywheels Ford xflows essex V6s and it works superb, best done with other mods when you want the motor to jump on to the cam powerband as quick as possible,,i have tryed to put this in real basic terms so many can understand,so please dont piss on this reply ive kept it simple,if you want it easier still,taken to extreme a over lightened flywheel, its the equivalent of trying to climb a hill on a four cylinder motor with a lead off one of the plugs.
The hill climbing example raises an interesting question. Does the flywheel inertia affect the power output available at constant revs? Simple theory would suggest that it doesn't, and that the gains only occur while the engine is accelerating. But presumably the reduced inertia also affects the cyclic speed changes inside the engine and it's conceivable that this would increase or reduce the net power output even at constant rpm?
Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff