Lightweight Flywheel

[SaM]

Thanks for all the feedback. Seems to be a bit of a hot topic haha. I already have a new clutch so im just after the flywheel. Seeing that mx5 manias cheapest is $545 and the two overseas ones are both under $300, i think its either going to be either the Exedy 12 lbs or Flyin Miata 13.5 lbs one.

[droo]

On my previous car, i removed the flywheel and got as much weight trimmed off the periphery as i could. It ended up being 1/3 lighter then standard. Edges were trimmed off and a fair few holes were drilled through non structural areas. Metal around the clutch mounting points was left intact for strength.

There were heaps of articles online warning that the car would stall easily and that you'd have no inertia going up hills. Load of bs, the change made the engine rev up heaps easier - no performance gain there other then making my car sound more like racecar.. Also having a spare flywheel and a front wheel drive car, the clutch/flywheel could be changed in well about 4-5 hours by myself.
With the lightened wheel, drivability felt much more responsive, being turboed it had more immediacy in throttle response and in 1st, and 2nd gears, revved noticeably faster to redline.

Changing gears was smoother as the engage point revved the engine down much faster and with much less effort and to me, felt a lot smoother and it was effortless to make nice clean smooth changes without jerking passengers heads.

I dont know where the internet warnings come from, as my experience with lightened wheels is completely the opposite to what i've read online.

My roadster has some Toda lightweight wheel on too (was on the car when i got it).
I wish it was lighter but i'm glad it's not a stocker. Don't forget the clutch assembly is pretty weighty too so its going to be added to rotational mass.

If/when i change the gearbox or clutch next time, i'll be definitly going a 1.6 clutch and lightened flywheel combo. When i did my rebuild, after my headwork i ran out time to order the clutch/flywheel to get the car on the road by a certain time.. My brother says the 1.6 roadsters feel 'sweeter' in their revving, and i'd bet my lunch that most of that would be attributed to a lighter flywheel.

[Apu]

Thanks for all the feedback. Seems to be a bit of a hot topic haha. I already have a new clutch so im just after the flywheel. Seeing that mx5 manias cheapest is $545 and the two overseas ones are both under $300, i think its either going to be either the Exedy 12 lbs or Flyin Miata 13.5 lbs one.

Did you call Mania or just look on there website? And does the $300 include shipping?

[mrpham]

Thanks for all the feedback. Seems to be a bit of a hot topic haha. I already have a new clutch so im just after the flywheel. Seeing that mx5 manias cheapest is $545 and the two overseas ones are both under $300, i think its either going to be either the Exedy 12 lbs or Flyin Miata 13.5 lbs one.

Contact MX-5 Plus/Automotive Plus here in Brisbane, they do a 1.6L lightened flywheel for a very good price.

[project.r.racing]

On my previous car, i removed the flywheel and got as much weight trimmed off the periphery as i could. It ended up being 1/3 lighter then standard. Edges were trimmed off and a fair few holes were drilled through non structural areas. Metal around the clutch mounting points was left intact for strength.

I dont know where the internet warnings come from, as my experience with lightened wheels is completely the opposite to what i've read online.

This is a good example of how different weight flywheels have different effects. without knowing the car/flywheel, but a lightened one doesn't have the drawback a lightweight on has.

Take a 1.6 flywheel for example. 7.2kg-ish. I have mine shaved and lightened down to 6.0kg-ish. But you can buy a toda one what weights 3.6kg. Even dropping the 1.2kg make a world of difference. And there is alot of other lightweight wheels out there also.

[Mr Morlock]

No Droo I do not think it is a "Load of bs," Personally I would take my cue from an expert.

Here are some comments on this topic from ex OEM engineer who specialised in engines

1. Lightening flywheels on modern engines is really not necessary unless you are racing the car. For a race car, it needs to be combined with other changes (lightweight pressure plate, and a racing clutch plate) to provide a significant benefit.
2 Flywheel mass on a modern engine is optimised to ensure good idle quality - reducing mass will have a negative effect on idle quality - i.e. potential to introduce roughness.
3. Flywheel mass on a modern engine is optimised to ensure good NVH at low rpm in tall gears - reducing mass will have a negative effect and could introduce roughness at low rpm in tall gears - i.e. less engine flexibility or reduced useable engine speed range.
4 Flywheel mass on a modern engine is optimised to reduce vibrations in the crankshaft - reducing mass could potentially result in a crank fatigue life issue long term.
5 Flywheel mass on a modern engine is optimised to provide sufficient clutch thermal capacity for multiple hill starts at maximum GVM - reducing mass could result in increased clutch temperatures (wear) under severe conditions.
6. Flywheel mass on an MX-5, in my opinion, is already low enough to allow you to make fast up-changes changes without having to wait too long for the engine revs to drop
7 Engine acceleration on an MX-5 is "adequate", although lightening the flywheel will marginally increase the rate at which revs increase in low gears.
8. You will struggle to notice a difference if you lightly machine the back of the factory flywheel; you really need to take off a lot of material to make a significant difference, because the flywheel is just one element that contributes to the rotational inertia of the engine. Other parts that have rotational inertia are the pressure plate, clutch plate, crankshaft, and front pulley/damper asy.
9. A much more effective approach than machining the flywheel is to purchase an aftermarket aluminium flywheel for a race car.

[wozzah1975]

No Droo I do not think it is a "Load of bs," Personally I would take my cue from an expert.

Here are some comments on this topic from ex OEM engineer who specialised in engines

1. Lightening flywheels on modern engines is really not necessary unless you are racing the car. For a race car, it needs to be combined with other changes (lightweight pressure plate, and a racing clutch plate) to provide a significant benefit.
Being a modern engine has absolutely nothing to do with how the engine will respond to flywheel weight reduction, any engine will respond the same, in fact on late model engines flywheels are excessively heavy in comparison to alot of early suff, so more noticelable when weight is removed. Does, it give you more power, No, but the responsiveness is significantly better, so if thats the way you like you car to feel it's a good mod.
2 Flywheel mass on a modern engine is optimised to ensure good idle quality - reducing mass will have a negative effect on idle quality - i.e. potential to introduce roughness.
Abolutely 100% correct if you take things to the extreme, ask yourself this though, how long does you car idle for when you are driving it??? to make any issues with the idle on an MX5 means excessive weight reduction anyway (I would suggest anything around 3.5kg total flywheel weight), not what the OP is aiming for
3. Flywheel mass on a modern engine is optimised to ensure good NVH at low rpm in tall gears - reducing mass will have a negative effect and could introduce roughness at low rpm in tall gears - i.e. less engine flexibility or reduced useable engine speed range.
My engine runs massive cosworth cams and has a 4.5kg flywheel currently, 500 gram harmonic, light weight clutch, is on carbs, it will still pull from 3500rpm in a tall gear, and idles with a light lope at 1000-1200rpm. The amount of weight we're talking about here is barely noticable, if at all in the scenario we have here, in fact if I had 2 identical cars for you to back to back drive on this exact situation I would almost bet my left testicle that you wouldnt be able to tell the difference
4 Flywheel mass on a modern engine is optimised to reduce vibrations in the crankshaft - reducing mass could potentially result in a crank fatigue life issue long term.
Massive weight and dual mass flywheels are purely there for noise, nothing else. I have seen more failures of crankshafts on late model vehicles with big weight flywheels in the last few years than I have my entire life, and I also blame the crank cracking issue in the MX5 on there being an incorrectly massed flywheel there in the first place
5 Flywheel mass on a modern engine is optimised to provide sufficient clutch thermal capacity for multiple hill starts at maximum GVM - reducing mass could result in increased clutch temperatures (wear) under severe conditions.
this is where it gets a bit technical. Standing starts are nicer with a heavy flywheel, and there is argument around the drag racing guys about the optimum weight of a flywheel for launching the car vs the benefits of engine acceration after you're moving. In regard to the temperatures, if the flywheel is lightened correctly, or made out of the appropriate material the temp will be almost unchanged, in fact in some cases cooler with newer materials on flywheels and friction plates. I still challenge you to drive a car with a sensible weight reduction given the amount here and pick the difference in this scenario as well though
6. Flywheel mass on an MX-5, in my opinion, is already low enough to allow you to make fast up-changes changes without having to wait too long for the engine revs to drop
Don;t agree, for the engine size the OE mazda unit is a lump, and very very heavy
7 Engine acceleration on an MX-5 is "adequate", although lightening the flywheel will marginally increase the rate at which revs increase in low gears.
that boils down to personal preference. I prefer the engine to feel very responsive, hence I like the lighter flywheels
8. You will struggle to notice a difference if you lightly machine the back of the factory flywheel; you really need to take off a lot of material to make a significant difference, because the flywheel is just one element that contributes to the rotational inertia of the engine. Other parts that have rotational inertia are the pressure plate, clutch plate, crankshaft, and front pulley/damper asy.
3+kg in the right area is very noticable, and very easy to remove off a Std wheel, and furthermore with its diameter it carries the most inertia of any single component in the rotating assembly of the engine, so any weight removal as little as it is from this component makes the most difference.

9. A much more effective approach than machining the flywheel is to purchase an aftermarket aluminium flywheel for a race car.
Depends what you aim to acheive, but I think that an excessive weight reduction is the wrong advise for a car you drive on a regular basis on the road, and that is when you may not like what it does to your car. And it is alot more expensive

Cheers, Woz

[Mr Morlock]

I would take the advice of a professional OEM engineer- if a major OEM employs someone to design/ implement engine programs that says something. Its pretty clear people will do whatever they want without actually taking account of facts. Most of the time people ask for advice but only wait for someone to agree. Its often a waste of time bothering to reply.

[gslender]

I would take the advice of a professional OEM engineer- if a major OEM employs someone to design/ implement engine programs that says something. Its pretty clear people will do whatever they want without actually taking account of facts. Most of the time people ask for advice but only wait for someone to agree. Its often a waste of time bothering to reply.

You are correct about OEM employing qualified and experienced engineers, and in some cases they are the best people with tremendous experience. But equally so, many large corporates make tremendously stupid decisions, often with full knowledge they are doing so. Many factors contribute to this; cost and budgets; marketing and study groups; mgmt commitment to time and resources. None of those are the best outcome for driving and engine performance, and yet they are part of the OEM pie when designing and building engines. It is the very reason that the NA6 got such a poorly designed cooling system - do you think the engineers wanted to muck up the cooling head flow?

So yes, OEM does spend more resources and effort in looking into the engineering, but no, it doesn't always end up in the car you buy.

G

[project.r.racing]

Just remeber also the NA6 and NA8 flywheels were not originally designed for the MX5. The NA6 one was being used 4 years earlier on a BD 323. Then plonked into a MX5. Supports the above post.

Back in the early 90s. Mazdaspeed made a NA6 flywheel that was 6.2kg from memory. That was probably tested and tried over various weights to finally allow MAzda to pick the perfect weight. Probably the first time the flywheel had been redesigned in 5 years since it's first release.

[wozzah1975]

I would take the advice of a professional OEM engineer- if a major OEM employs someone to design/ implement engine programs that says something. Its pretty clear people will do whatever they want without actually taking account of facts. Most of the time people ask for advice but only wait for someone to agree. Its often a waste of time bothering to reply.

Like gslender said, in alot of instances we don't see the results on a motor vehicle, and in my experience with certain engineers, they sometimes simply get it wrong. You would think that in this day and age that major OEM do employ top notch people for the job, yet I would be here a week listing engineering faults on motor vehicles...... So are they really that immune to making mistakes?...... Furthermore the engine design is 40+ years old, and the engineering technology we have here dates back to 1985 (B6 DOHC), I would hope that alot has been learnt since then (some good, some bad).

Basing your opinion and thoughts from talking to one individual can be misleading, as I am sure if you spoke to another OEM engineer there would be a difference of opinion and thought on the matter, otherwise all our cars would be the same.

I also agree certain individuals will ask for advice and then proceed to do whatever they want afterward, in my work I get that alot. Unfortunately its a part of life now with so much access to info. The key is sifting through the information you have been given and trying to make an informed decision from that.

Cheers
Woz

[manga_blue]

I've been involved in engineering design, development and project management for a few more decades than I'd care to admit to. Every project is in constant tension between quality, time and cost factors. It's very plain to see where the design quality decisions lost out to cost and expediency factors in converting the B6/BP engines from a FWD sedan to a RWD sports car unit:
1. Coolant flow: bodged job done on the cheap
2. Fuel mapping: ridiculously rich values in lieu of proper testing and tuning.
3. Flywheel weight: clearly a comfortable sedan size sourced off the shelf rather than retooling for an appropriate size
4. Crankshaft nose design(s): initially adequate for a low revving sedan, it appears to have been done in 2 or 3 stages by the work experience student

BTW my flywheel is OEM with most of the ouiter lip machined off to bring it done to about 6.5Kg (or about the same as Mazda decidied it should be for the Mazdaspeed). At that weight it's still very easy to get rolling, it idles just as well and quick changing is noticeably better. It has a marginal influence on performance: if you look at the total the angular momentum of the engine, flywheel assembly. gearbox, diff, brakes and wheels then you'll find the flywheel is only a minor proportion of that. It only really has any performance effect in 1st and 2nd gears. I'd say it's a must mod for motorkhana and tight hillclimbs but pretty marginal for an open circuit like Eastern Creek or Phillip Island.

[Mr Morlock]

Road cars we were talking about.

[Apu]

My MX5 is a daily, and I have no trouble with the lightened flywheel. How many cars have you had with a lightened flywheel Morlock?

[manga_blue]

Road cars we were talking about.

Sports cars we are talking about.