34 replies to this topic

[johnny yuma]

Aside from driveability issues,what are the pros and cons of lightened flywheels on mass produced engines modified for performance ? Are there tangible benefits ,or are they too small to measure or consistently improve lap times ?

[Fat Boy]

Aside from driveability issues,what are the pros and cons of lightened flywheels on mass produced engines modified for performance ? Are there tangible benefits ,or are they too small to measure or consistently improve lap times ?

Probably the easiest to measure advantage would be engine spin-up on downshifts. Unless the flywheel were very, very large, it would not measurably effect lap times.

Having said that, I've stuck more than one on a lathe....

[Lee Nicolle]

It is quite measurable. The engine will be more responsive off slow corners, it will rev more freely and the engine braking will be better.
Downside it will be more 'grumpy' at low RPM and easier to stall when trying to take off at low RPM.
Getting rid of centrifigal mass is equally as important; eg take the weight from the outside diameter more than the inside is conducive for engine response.That is why any serious race engine has a small diameter lightweight clutch. Heavy flywheels and large diameter clutches are for trucks.
A light flywheel and small clutch will make an average engine far more responsive which seems like more power.
Realistically it will make no more real dyno horsepower BUT make what you have far more useable.
Engine balancing must be taken into account though usually not a great hassle.And on your earlys Johnny they have a nuetral balance flywheel so just balance the flywheel and clutch and bolt it on.
A mildly lightened flywheel does with a full size standard clutch does not make a terrible difference in streetability but a real light one with a small clutch defenitly will.
On the Cleveland I am currently playing with the weight has gone from 45lb down to about 20lb and it makes a huge difference.
Do not lighten cast iron flywheels too much as they may explode. On an early about 7lb, and try to take it friom the outside diameter as much as possible. Use the standard diameter clutch with a button ceramic clutch plate which will take any decent grey with ease.
I have had flywheels machined from 1" steel plate which you can machine thinner and lighter than iron, down to about 10 lb safely.

[johnny yuma]

Thanks Lee--not looking for greymotor tips this time,a mate of great knowledge swears you would get more usable power from any engine generally with a lighter flywheel ,but my opinion is sure it might rev snappier in neutral but in gear you'd not detect it on the track or a dyno.

[Fat Boy]

Thanks Lee--not looking for greymotor tips this time,a mate of great knowledge swears you would get more usable power from any engine generally with a lighter flywheel ,but my opinion is sure it might rev snappier in neutral but in gear you'd not detect it on the track or a dyno.

And you would be correct. It's not a difficult thing to figure out. Figure the inertia of your clutch/flywheel and then sort out the power that is used to accelerate while gears are engaged. In Lee's example, going from a 45# assembly to a 20# assembly (which is a hell of a change), it would probably be detectable in first gear when the engine rate of acceleration(as opposed to the whole car) is quite high. Unfortunately, at those times, you're often traction limited, so the gain may not be realized. In high gears, the engine accelerates slowly, so the change in kinetic energy due to engine inertia is not nearly as important as, say, aerodynamics.

Like I said, I keep things light as possible as a matter of course, but don't expect to be able to see it on a stopwatch.

[johnny yuma]

THANKS FB. Shedding a few kilograms from the car's weight is always good. Then you can add a bit onto the Harmonic Balancer !!

[gordmac]

The weight you take off will not be terribly significant, the reduction in inertia however may be. It is possible to calculate an equivalent mass for the inertia, this is effectivley multiplied by the overall gear ratio so will be more in 1st and less in top. How noticable it would be is I suspect very car dependant, I am guessing but may be more significant for haavyish lowish powered cars.

[Lee Nicolle]

And you would be correct. It's not a difficult thing to figure out. Figure the inertia of your clutch/flywheel and then sort out the power that is used to accelerate while gears are engaged. In Lee's example, going from a 45# assembly to a 20# assembly (which is a hell of a change), it would probably be detectable in first gear when the engine rate of acceleration(as opposed to the whole car) is quite high. Unfortunately, at those times, you're often traction limited, so the gain may not be realized. In high gears, the engine accelerates slowly, so the change in kinetic energy due to engine inertia is not nearly as important as, say, aerodynamics.

Like I said, I keep things light as possible as a matter of course, but don't expect to be able to see it on a stopwatch.

That is clutch and flywheel combined. Genuine ford twinplate and iron flywheel to a Tilton Nascar assembly.
About40lb down to 20lb on a Chev, Windsor or Mopar. About 33lb down to about 17 for a Holden 6. With those asemblys they also lose a lot of centrifigual weight [inertia] which can be more important. Even at 100 mph the engine feels and is more responsive to the throttle
On a Chev I have found a need for quite a light balancer 6-7"] too as otherwise the crank cracks after extended periods.
Sprintcars are ofcourse the ultimate with no flywheel or balancer and a light ring weight on the crank too. That is why they sound so responsive.
Flywheel weight will make little difference in actual HP but alters the engine response a heap. Though a light reciprocating mass makes a lot of HP

[johnny yuma]

Sprintcars are ofcourse the ultimate with no flywheel or balancer and a light ring weight on the crank too. That is why they sound so responsive.

Interesting,once they are push started and rolling the back wheels are probably acting like flywheels ! Never takes much time to get them to overcome their inertia on a dirt oval !!

[Lee Nicolle]

Interesting,once they are push started and rolling the back wheels are probably acting like flywheels ! Never takes much time to get them to overcome their inertia on a dirt oval !!

Yes the wheels are flywheels as on all cars.But a Sprinter rim does not weigh much either and nor does the tyres though they get bigger every year in both width and diameter. A left rear these days is the same as a right rear 10 years ago.

Wheels and tyres on all cars are flywheels, besides the obviuos of unsprung weight both the weight and diameter effect accaration and throttle response. The biggest widest tyres and rims are often not the answer.
Classic example of that at the moment is those boring 'Wingless sprints' that are using a wheel tyre combo which works ok on a 410 Sprinter but is a total waste of power and throttle response on stock V6 3.8 with a quarter [maybe] of the 410s power.

[Ray Bell]

Trying to get my head around the harmonic balancer issue...

I almost see this as a partner to the flywheel, balancing (if you will) the effect of the flywheel on one end of the crankshaft by providing inertia on the other end. Would that need to be reduced in concert with flywheel weight... assuming, of course, that the starting point has them at the right weights?

[Greg Locock]

Trying to get my head around the harmonic balancer issue...

I almost see this as a partner to the flywheel, balancing (if you will) the effect of the flywheel on one end of the crankshaft by providing inertia on the other end. Would that need to be reduced in concert with flywheel weight... assuming, of course, that the starting point has them at the right weights?

No. the mass of the balancer is only half the story, the other is the stiffness of the rubber. I don't think the torional mode of the crank changes frequency /much/ as you change the flywheel inertia (because it is still much greater than the inertia of the crank), so the tuned fequency would have to stay roughly the same. I wouldn't change the mass either, the excitation is just as strong, and the system damping won't have changed.

The first diagram in this shows why, a quck scan says this article is on the right rack http://www.bhjdynami...Damper_Info.pdf


and towards the end he's even got a good waterfall plot of TVs vs frequency.

[Lee Nicolle]

Trying to get my head around the harmonic balancer issue...

I almost see this as a partner to the flywheel, balancing (if you will) the effect of the flywheel on one end of the crankshaft by providing inertia on the other end. Would that need to be reduced in concert with flywheel weight... assuming, of course, that the starting point has them at the right weights?

Harmonic balancers damp out the viabration transmitted into the crankshaft by engine reciprocation and flywheel clutch etc.
A standard rubber type balancer is ok on std and near std engines but needs to be upgraded as the RPM and engine loads increase.Some upgraded ones are made from better elastimers with mechanical means of stopping the outer from parting with the inner.Some are fluid filled. Most performance balancers are made lighter than original and are made from material that does not explode unlike an original usually made from cast iron.

As I found a bigger balancer is not better, I was advised to downsize from 8" to 7" and about half the weight on my 358 Chev with an 18lb clutch and flywheel.

In the old days people were doing that sort of develoment, Beecheys EH had a Mercedes mercury filled balancer.These days you can generally buy something ready made for most popular engines.
Most 4 cyl engines do not use one as the crank is fairly short, though the viabrations usually are worse.
Most 6 cyl engines need one, usually improved. 202 Holdens are quite bad as the spit the outer ring off, shake flywheels loose and all the accescories off the engine.Yet never seem to crack cranks!! The counterweight cranks are better but are 15 lb heavier!
Most V8s use one, though the cranks are short they have a lot of recirocating mass on them, though for race use better quality and lighter is generally better.

Sprintcar engines normally never use one as they have no flywheel though they do drive a fair bit of stuff from both the crank and cam, oil pumps, power steer pumps, water pumps, hydraulic wing pump etc.
Though for mine i do think they could use something as the harmonics and drive loads break steel cams fairly regularly. But HP is HP and the engines have a fairly short service life.Though the balancing and components are generally far better than production engines, internally balanced etc.

Most Nascar and Supercar engines use a trick light balancer and most are driving the cam with a toothbelt which takes a fair bit of the valve train harmonics out of the engine. And the cam timing stays where it is supposed to be.

[Ray Bell]

I think there's a great deal more to the story than that...

My understanding is that the harmonic balancer's job is to basically even out the speed of the front of the crank during uneven firing pulses. And that assumes that all firing pulses are uneven, as they move up and down the crank.

Pretty sure I've got that right.

Beechey's S4 used a Bristol balancer, by the way. Muir's used a Dodge.

[gruntguru]

My understanding is that the harmonic balancer's job is to basically even out the speed of the front of the crank during uneven firing pulses. And that assumes that all firing pulses are uneven, as they move up and down the crank.

Sort of. The problem is actually torsional vibration or oscillations of the crankshaft, with the crankshaft acting as a torsional spring and the various masses attached to the crankshaft. This system will oscillate naturally at a number of (resonant) frequencies. If the impulses caused by firing (or just the stop-start motion of the pistons) are occurring at one of those frequencies (especially the fundamental), the natural oscillation of the crankshaft can become excessive. Think of a car with the dampers removed - you can make it oscillate quite violently with perhaps only one finger, as long as your input is at the right frequency.

The typical rubber/mass harmonic balancer helps in two ways.
1. It forms a spring mass system of its own (the rubber being the spring) with a natural frequency chosen to oppose the oscillation of the crankshaft.
2. During operation near a critical speed the rubber acts as a damper to absorb some of the energy and reduce the oscillation.

[johnny yuma]

Various engine layouts have their wobble period.An inline 6 kicks in around 6300 rpm,an inline 4 about 9000 rpm.But most street engines as manufactured until recently did not operate at those revs ,but still ran Harmonic balancers with rubber insulator as good practice.
The Holden greymotor is a unhappy over 6300 especially with it's 4 Main bearing crank,and for decades a heavy harmonic balancer has been the golden rule for road race motors---and yet speedway midgets in their day ran no flywheel or balancer with apparently better crank life expectation than their road racing cousins.Something here I don't understand.Perhaps they merely kept below 6000 rpm !

Of course the development of counter rotating balance shafts has meant big 4 cylinder engines are smooth now,EVEN 5 CYLINDER ENGINES !

Edited by johnny yuma, 23 December 2009 - 00:54.

[gruntguru]

Various engine layouts have their wobble period.An inline 6 kicks in around 6300 rpm,an inline 4 about 9000 rpm.But most street engines as manufactured until recently did not operate at those revs ,but still ran Harmonic balancers with rubber insulator as good practice.
The Holden greymotor is a unhappy over 6300 especially with it's 4 Main bearing crank,and for decades a heavy harmonic balancer has been the golden rule for road race motors---and yet speedway midgets in their day ran no flywheel or balancer with apparently better crank life expectation than their road racing cousins.Something here I don't understand.Perhaps they merely kept below 6000 rpm !

Of course the development of counter rotating balance shafts has meant big 4 cylinder engines are smooth now,EVEN 5 CYLINDER ENGINES !

Balance shafts are not related to harmonic balancers and torsional vibration.

[Lee Nicolle]

Various engine layouts have their wobble period.An inline 6 kicks in around 6300 rpm,an inline 4 about 9000 rpm.But most street engines as manufactured until recently did not operate at those revs ,but still ran Harmonic balancers with rubber insulator as good practice.
The Holden greymotor is a unhappy over 6300 especially with it's 4 Main bearing crank,and for decades a heavy harmonic balancer has been the golden rule for road race motors---and yet speedway midgets in their day ran no flywheel or balancer with apparently better crank life expectation than their road racing cousins.Something here I don't understand.Perhaps they merely kept below 6000 rpm !

Of course the development of counter rotating balance shafts has meant big 4 cylinder engines are smooth now,EVEN 5 CYLINDER ENGINES !

Midgets never had a flywheel and a season of midget racing was about the same distance as one road race meet.
Though speedway is quite hard on engines, as is methanol.
Most good Grey midget engines ran over 7000, some budget runners ran far less but still got in the danger area.
Inline 6s have different problem period, depends on the bore and stroke and crank and head design.
Re balance shafts, most Sigma style engines when raced do away with the 'silent' shaft, not certain about others.

[Ray Bell]

Yes, to be clear on the purpose of balance shafts...

They introduce a secondary out of balance phase to an engine to counter the imbalance in the crank. It's a comfort thing, not a cure for the primary problem.

[saudoso]

Of course the development of counter rotating balance shafts has meant big 4 cylinder engines are smooth now,EVEN 5 CYLINDER ENGINES !

I had a 5 cylinder for 8 years, that Fat was smooth and sang beautifully.

[Greg Locock]

Yes, to be clear on the purpose of balance shafts...

They introduce a secondary out of balance phase to an engine to counter the imbalance in the crank. It's a comfort thing, not a cure for the primary problem.

Slight pickiness, they are to counteract the second order forces due to the non sinusoidal motion of the piston and conrod. That is, a perfectly balanced crank on most engine configs (except an I6 and relatives) would still need a balance shaft to eliminate this effect. You can still see some (it is very small) 2nd order on an i6 because the crank is flexible, in some respects designing the crank for an I6 is a bit like designing 6 single cylinder cranks - that model is very useful when you are designing the crank web counterweights.

[McGuire]

One point not raised yet... you want to be careful with lightened or otherwise cut-down flywheels on front-engine cars where the driver is in the path of flying pieces. Sensible racing associations require ballistic bell housings or shields for just this reason. A shattered flywheel and associated flying clutch components can cut an entire car apart. The stock bell housing and floor pan will barely slow them down.

[Lee Nicolle]

One point not raised yet... you want to be careful with lightened or otherwise cut-down flywheels on front-engine cars where the driver is in the path of flying pieces. Sensible racing associations require ballistic bell housings or shields for just this reason. A shattered flywheel and associated flying clutch components can cut an entire car apart. The stock bell housing and floor pan will barely slow them down.

Worse on left drive cars. I saw a speedway sedan with an alloy flywheel explode many years ago. happened at around 8000rpm and it cut through the left chassis rail, cut the header in half plus all the floor etc. Car ended up in the fence fairly gently but still more damage. The scattershield did live though was fairly battered.
Another case was in drag racing where an exploding illegal cast iron flywheel did fairly severe injuries to a girl in the crowd at least 60 feet way.
That is why I have never used cast iron flywheels that have more than moderate lightening. And do not turn them too hard either.

[Catalina Park]

At Bathurst one year the car in front of me punctured his back tyre with his harmonic balancer. I bet that gave him a shock.
It looked good from behind though.

Edited by Catalina Park, 24 December 2009 - 08:22.

[McGuire]

In the early years of drag racing, dozens of people were killed by flywheel and clutch shrapnel while countless more were injured. Wayne Erickson was a Chrysler engineer and one of the original Ram Chargers, along with Tom Hoover, Billy Shope, et al. Driving his '53 Dodge at the 1959 US Nationals, he was severely burned when the fuel line was severed by a flywheel shard and the car lit up. It was pretty bad, took him over a week to die... best to be hoped for given the state of burn treatment at the time.

[Lee Nicolle]

[quote name='Catalina Park' date='Dec 24 2009, 08:20' post='4052523']
At Bathurst one year the car in front of me punctured his back tyre with his harmonic balancer. I bet that gave him a shock.
It looked good from behind though.
[/quote
In any other form of racing you are allowed and should bolt the balancer on and use a retainer plate to keep the outside ring on. HQ racing was always a lesson in harmonics. They seemed to crack a lot of blocks too.

[SteveCanyon]

I'll have to disagree with the notion that having a lightweight flywheel does little for acceleration, as I have tried it in real life in a car that had that done ( 7kg flywheel down to a 3kg alloy one) though there was also a close-ratio gearbox change as well. But the top two gears were basically identical and yes I could certainly feel the car accelerate nicely in the lower gears I could also feel it accelerate noticeably better in the top two.
I really wasn't expecting this, as according to the theory that several people told me I just wouldn't.
I don't have datalogging to back it up but the calibrated arse-o-meter that has spent nearly twenty years in the car knows it very well indeed.

On the new engine for my new racing car, I will not be running a flywheel as such, only a small diameter dual-plate clutch. It'll just have a thin flexplate (or whatever they're called) from an automatic gearbox to hold the ring gear in place. They weigh approximately naff-all.

Billzilla.

Edited by SteveCanyon, 27 December 2009 - 14:10.

[Greg Locock]

Couldn't that be largely the cumulative effect from the better acceleration in the lower gears? that is you get a slightly better launch out of the preceeding corner, all your shift points move back by 1/2 m, and you have 100 rpm more at your brake point, and you think, wow, this thing is really moving on the straights? Just a theory.

I don't think anyone is saying it isn't worth lightening the flywheel in a circuit car are they?

[SteveCanyon]

Couldn't that be largely the cumulative effect from the better acceleration in the lower gears?

I perhaps should have said that it was starting from a constant speed in 4th or 5th gear, not from the leftovers from the lower gears.

Billzilla

[gruntguru]

I'll have to disagree with the notion that having a lightweight flywheel does little for acceleration, as I have tried it in real life in a car that had that done ( 7kg flywheel down to a 3kg alloy one) though there was also a close-ratio gearbox change as well. But the top two gears were basically identical and yes I could certainly feel the car accelerate nicely in the lower gears I could also feel it accelerate noticeably better in the top two.
I really wasn't expecting this, as according to the theory that several people told me I just wouldn't.
I don't have datalogging to back it up but the calibrated arse-o-meter that has spent nearly twenty years in the car knows it very well indeed.

On the new engine for my new racing car, I will not be running a flywheel as such, only a small diameter dual-plate clutch. It'll just have a thin flexplate (or whatever they're called) from an automatic gearbox to hold the ring gear in place. They weigh approximately naff-all.

Billzilla.

Bill, at this rate you are going to run out of noms de plume very soon. Who the hell is Steve Canyon anyway?

4kg is a lot of weight saving from a flywheel and even though the equivalent vehicle mass savings increase with the square of the gear ratio, 4kg would still produce noticeably improved top-gear acceleration in a lightweight, high-revving vehicle. Equivalent mass saved in top gear might be as much as 20kg.

Of course if the same vehicle has 4:1 1st gear and 1:1 top gear, the mass saved in first would be much greater (about 260kg) and much more noticeable. (260 = [{20-4kg} x {4}^2]+4kg)

[cheapracer]

Bill, at this rate you are going to run out of noms de plume very soon. Who the hell is Steve Canyon anyway?

He's a Hollywood Star on the side Mate.

I'm not a big knowlegeable person on Holden Grey motors but didn't they break at around a substained 6300 but no problems under or over or accelerating through that?

[gruntguru]

He's a Hollywood Star on the side Mate.

I'm not a big knowlegeable person on Holden Grey motors but didn't they break at around a substained 6300 but no problems under or over or accelerating through that?

I didn't know Bill drove an FJ.

[johnny yuma]

Christmas finds me with "The Jack Brabham Story"...(Your brother always knows what you might like ! ) . Page 36 ,the year is 1953 ,and in the grand tradition of stumping up big quids for a shagged racecar Jack has just taken delivery of a Cooper Bristol Mk 2 (later RedEx Special) which is in need of a good deal more than a tune-up. In reworking the motor Jack is amazed that the Flywheel and Clutch assembly weighs an astounding 75-85 lbs (34-38 kg). After the first few runs in the rebuilt Bristol,Jack fabricates a Harley Davidson clutch similar to his midget speedcar, with machined down the flywheel, for a total weight of 15-17 lbs (7-8kg)and fits them .In Jack's words,the "acceleration of the car was greatly improved" . That's good enough proof for me ...... but this is quite an extreme case !
BTW John Medley is quoted on page 39 reporting on a match race at Mt Druitt between Jack and Horace Gould from England in another Bristol-Cooper, which Jack hoses off comprehensively,in part possibly due to the lighter clutch/flywheel ,which allowed the RedEx special rev reliably to 6500 instead of 5800 in the perceived wisdom ,as the bad effects of a huge mass at one end of the crank were reduced.John, he left you off the index, but hells bells you've been out and about a long time well done ! You must have been all of 15 years old , tops ?

Edited by johnny yuma, 31 December 2009 - 08:31.

[john medley]

Compliments of the season to you Mr Yuma.

Correct , actually 14

[Lee Nicolle]

Christmas finds me with "The Jack Brabham Story"...(Your brother always knows what you might like ! ) . Page 36 ,the year is 1953 ,and in the grand tradition of stumping up big quids for a shagged racecar Jack has just taken delivery of a Cooper Bristol Mk 2 (later RedEx Special) which is in need of a good deal more than a tune-up. In reworking the motor Jack is amazed that the Flywheel and Clutch assembly weighs an astounding 75-85 lbs (34-38 kg). After the first few runs in the rebuilt Bristol,Jack fabricates a Harley Davidson clutch similar to his midget speedcar, with machined down the flywheel, for a total weight of 15-17 lbs (7-8kg)and fits them .In Jack's words,the "acceleration of the car was greatly improved" . That's good enough proof for me ...... but this is quite an extreme case !
BTW John Medley is quoted on page 39 reporting on a match race at Mt Druitt between Jack and Horace Gould from England in another Bristol-Cooper, which Jack hoses off comprehensively,in part possibly due to the lighter clutch/flywheel ,which allowed the RedEx special rev reliably to 6500 instead of 5800 in the perceived wisdom ,as the bad effects of a huge mass at one end of the crank were reduced.John, he left you off the index, but hells bells you've been out and about a long time well done ! You must have been all of 15 years old , tops ?

Listen to an A model powered midget. The flywheel clutch assembly on those weigh over 70lbs! So no flywheel really makes them sound sharp!
The grey Holden midgets seemed to have less crank problems though most ran under or over that critical speed.At times 7500 plus though I honestly cannot see how they made power at that RPM. [Except Repcos and Waggots]