Light flywheel: Worth it?

[tr7v8]

stevieturbo said:

tr7v8 said:

Correct, only 9kg in 5th. But acceleration normal infers lower gears.

Not really. In most motorsport, how often are you ever in 1st gear ? Not that often really. And most cars with any decent level of performance will be traction limited in 1st gear anyway ( unless 4wd )

So it's 2nd gear upwards that matters, where the possible benefits of a light flywheel are much diminished, almost negligable.

Every little bit can help, but is it worth it ? is a different matter.

For a light low powered vehicle then yes. For something heavier or making a respectable amount of power, any differences will be small.

I know I wouldnt go out of my way to source a light flywheel, but if a clutch kit happened to come that way, so be it.

The OP does say excluding out & out comp cars. Mine was a road car & the main reason for lightening it was the amazing weight of it! Traction in the dry was OK as I remember. It also made heel & toe so much easier. Idle was unaffected.

[PeterBurgess]

I attach an image of an experimental run on keith's (step son) kamper. The more powerful line is with the fan/alternator disconnected. We have determined a 6 blade mechanical fan took 3 bhp on an MGB, we also discovered the power steering conversion on a B took 3 bhp. We thought of that huge, flywheel weight cooling fan on the VeeDub (we were running the largest fan to help cool the high CR engine)....bloody hell we say, look what we have discovered...10 bhp for nothing Here we go we say, Keith wants to do a standing start 1/4 in under 18 secs with the minimum tuned engine possible this is the way to go....lets keep it secret! What do we discover? All those in the know already run down the strip 'sans' fan....no problem as engine only running for a few seconds...and we thought we had discovered something unknown to man I know it is not a flywheel only run but a few of the useable bhp probably came with losing the weight, as usual, it is almost impossible to remove all the independent variables when experimenting!

Peter

[stevieturbo]

tr7v8 said:

The OP does say excluding out & out comp cars. Mine was a road car & the main reason for lightening it was the amazing weight of it! Traction in the dry was OK as I remember. It also made heel & toe so much easier. Idle was unaffected.

Name any form or racing, or indeed enthusiastic road driving where most time is spend in 1st and 2nd gears ? Part from maybe autotesting.
If you're stuck in lots of traffic....you might appreciate a heavier flywheel lol

[carlt5]

stevieturbo said:

Name any form or racing, or indeed enthusiastic road driving where most time is spend in 1st and 2nd gears ? Part from maybe autotesting.
If you're stuck in lots of traffic....you might appreciate a heavier flywheel lol

All the various forms of the motorsport that arguably requires the most skill -
Trials

[PhillipM]

stevieturbo said:

Name any form or racing, or indeed enthusiastic road driving where most time is spend in 1st and 2nd gears ? Part from maybe autotesting.
If you're stuck in lots of traffic....you might appreciate a heavier flywheel lol

Any form of motorsport where you're allowed to change gearboxes. If you build a car you can't use 1st or 2nd gear in you'll be at the back of the pack in short order.

[stevieturbo]

PhillipM said:

Any form of motorsport where you're allowed to change gearboxes. If you build a car you can't use 1st or 2nd gear in you'll be at the back of the pack in short order.

Ive never come across a car yet where you cannot use all gears, so that's a strange comment

I asked how long is spent in those gears on an average race etc. Very little I'd imagine unless it's a very low speed of motorsport like autotesting
Any racing where the car travels fast, you'll rarely see the lower gears apart from at the start
Again, I ask how many forms of driving can you name where a lot of time is spent in 1st and 2nd gear ? Where a flywheel may make the most potential difference....even though it is still a very very small difference

So far only one has been mentioned, ie Trials. Although not exactly sure what they even are, as it is a bit vague

[PeterBurgess]

The trials talked about refers to very low speed driving/riding negotiating tight turns, rocks,streams generally damned nigh impossible to negotiate obstacles. With bike riding one tries not to put ones foot down or one losses points, with car trials there tend to be poles not to touch or one loses points. The trials can involve slightly higher speed hills or water sections, or boggy, muddy nasty stuff......also called Mud Plugging

Peter

[MFaulks]

Well in my experience, as pointed out in effect by Peter, it's the delta change in RPM that is being demanded, especially changing down gears where the spacing is less than idea - production hill climb classes for example where the lighter mass does have significant effect. Totally agree that this will have less effect as you go up the gears (and hopefully also better spacing), and same applies to the acceleration of mass in a lumped sense. Hence, in my case on a UN1 where 1st and 2nd are massively space (unfavourably), on some hill climb circuits first is needed and hard to catch due to matching engine rpm to that dictated by the road speed and dropping down a gear; conversely on acceleration same applies. But it is quite typical to only use 2nd and 3rd on most circuits, so lightened mass pays off.

[carlt5]

stevieturbo said:

So far only one has been mentioned, ie Trials. Although not exactly sure what they even are, as it is a bit vague

one of the oldest form of motorsport

Classic Trials
this club just celebrated 111 years
http://www.themotorcyclingclub.org.uk/

http://www.wheelspin.info/
http://www.actc.org.uk/

Sporting Trials
http://www.sportingtrials.com/introduction.htm

Car Trials
http://www.btrda.com/Car_Trials/

[PeterBurgess]

This is a shot of a customer's Escort trialling....a pretty steep climb!

Peter

[andygtt]

Pumaracing said:

andygtt said:

I lightened the flywheel/clutch in my noble massively... Basically I changed to a triple plate 7.25' clutch and halved the flywheel so almost all the reduction in weight was on the outer side of flywheel for maximum result. Lost nearly 10kgs!

I'd be interested to model that in my simulation program as an extreme example of flywheel lightening if you have sufficient details. Is there somewhere on the web with detailed car specs - gearing, tyre size, weight, drag etc?

What details would you need? all the stuff related to my specific car on the net are pretty generic!... think CD, gearing etc can be got though and I know exactly what my car weighs.

I weighed the old and new clutches etc... old one is on the shelf so can take more exact measurements lol

[Pumaracing]

stevieturbo said:

tr7v8 said:

I lightened the flywheel on my TR7V8 & lost around 3kg (the SD1 flywheel is massive!) It vastly improved the pick up & MAY have improved the acceleration. I say may as there were many other changes at the same time.
But a bit of fag packet maths, show that the 3kg reflected through the gearing meant it was the equivalent of losing around 30kG off the cars weight or around 2.5% of the kerbweight.

Perhaps in 1st gear, not in top gear.

No that's about right. 10kg of chassis mass per 1 kg of flywheel mass would, as I've said, quite easily be a reasonable average relationship for the whole performance curve of the car right up to high speed. In 1st gear only then 1 kg of flywheel mass could be equivalent to anywhere from 20 to 40 or more kg of chassis mass depending on gearing. More still on a bike engine.

[tr7v8]

Pumaracing said:

stevieturbo said:

tr7v8 said:

I lightened the flywheel on my TR7V8 & lost around 3kg (the SD1 flywheel is massive!) It vastly improved the pick up & MAY have improved the acceleration. I say may as there were many other changes at the same time.
But a bit of fag packet maths, show that the 3kg reflected through the gearing meant it was the equivalent of losing around 30kG off the cars weight or around 2.5% of the kerbweight.

Perhaps in 1st gear, not in top gear.

No that's about right. 10kg of chassis mass per 1 kg of flywheel mass would, as I've said, quite easily be a reasonable average relationship for the whole performance curve of the car right up to high speed. In 1st gear only then 1 kg of flywheel mass could be equivalent to anywhere from 20 to 40 or more kg of chassis mass depending on gearing. More still on a bike engine.

I worked it out as first is 3:1, FD is 3:1 so 3 x 3 is 9ish times 3kg is just under 30kG total.

[Pumaracing]

tr7v8 said:

I worked it out as first is 3:1, FD is 3:1 so 3 x 3 is 9ish times 3kg is just under 30kG total.

No. I gave the equation here.

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

[Pumaracing]

Pumaracing said:

tr7v8 said:

I worked it out as first is 3:1, FD is 3:1 so 3 x 3 is 9ish times 3kg is just under 30kG total.

No. I gave the equation here.

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

Hmmm. By hook or by crook despite the wrong method you've come close to the right answer. Assuming an average tyre radius of about 12 inches it then depends on where you've removed the flywheel material. Either mainly from the very o/d at an average radius of 5 inches or more evenly over the surface at an average radius of 3.5 inches. We then get in 1st gear either:

1) (3.1 x 3.1 x 3.5 / 12) squared x 3kg = 23.6kg

2) (3.1 x 3.1 x 5 / 12) squared x 3 kg = 48.1kg

Like I said previously. Low revving, high geared V8s aren't very sensitive to flywheel inertia.

[tr7v8]

Pumaracing said:

Pumaracing said:

tr7v8 said:

I worked it out as first is 3:1, FD is 3:1 so 3 x 3 is 9ish times 3kg is just under 30kG total.

No. I gave the equation here.

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

Hmmm. By hook or by crook despite the wrong method you've come close to the right answer. Assuming an average tyre radius of about 12 inches it then depends on where you've removed the flywheel material. Either mainly from the very o/d at an average radius of 5 inches or more evenly over the surface at an average radius of 3.5 inches. We then get in 1st gear either:

1) (3.1 x 3.1 x 3.5 / 12) squared x 3kg = 23.6kg

2) (3.1 x 3.1 x 5 / 12) squared x 3 kg = 48.1kg

Like I said previously. Low revving, high geared V8s aren't very sensitive to flywheel inertia.

The formula I used I remember from a CCC or similar artile by Vizard or maybe Andy Dawson from years ago.

[Evoluzione]

Thanks for all the replies on this, it's made for an interesting read and got some brain cells moving about a bit for me.

[reggid]

PeterBurgess said:

Dave

As you say you are simulating not measuring.

Why fools errand, if you owned and operated a dyno day in day out and had run water brake, inertia and Eddy brake as I have done everyday for 25 years you would maybe write a little differently.

Are you saying all the stuff on the link I posted above is incorrect?

We have already seen the difference in acceleration with lighter flywheels on an otherwise same car. It is interesting to note that Silkolene came to the same conclusions as we did, but you will probably say they are on a fools errand as well.

Maybe if you get to buy and run an inertia dyno you might share with the forum as I am happy to do? I am amazed how much I have learned running the inertia/eddy dyno for 2 and a 1/2 years, just goes to show when we think we know it all we actually know very little

Peter

Peter the problem with inertia dyno and measuring changes due to a flywheel are that the power absorbed in rotational energy is proportional to the angular acceleration of the flywheel. if the angular acceleration on the dyno does not match that of the driving car (i.e. most likely)then the gains are not quantitative.

[PeterBurgess]

Hiya

I never said you could get an accurate/scientific measurement, I said you can measure a difference if you lighten a flywheel. The difference will also show up in quicker acceleration on the road, I suppose it is showing potential on the inertia dyno. The figures are repeatable, therefore measurable, whether bhp, pinto beans or whatever, the differnce shows up.

Peter

[reggid]

PeterBurgess said:

Hiya

I never said you could get an accurate/scientific measurement, I said you can measure a difference if you lighten a flywheel. The difference will also show up in quicker acceleration on the road, I suppose it is showing potential on the inertia dyno. The figures are repeatable, therefore measurable, whether bhp, pinto beans or whatever, the differnce shows up.

Peter

you dont need a dyno to know that it will accelerate faster in every gear (faster in 1st and less in every subsequent gear proportional to square of gear ratio) or that it will show an increase on the dyno however large or small it may be depending on the acc rate of the engine, IMO determining the actual improvement with as much accuracy as practical is the goal otherwise why bother with a dyno at all?