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Thread: Lightweight Flywheel

  1. #11
    Still Plays With Cars Loren's Avatar
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    Weight is always a factor. knocking another 10 pounds off of a 2000 pound car is always a good thing. That's a half a percent improvement in itself.

    But, that's not the main reason for a lightweight flywheel. There are a few good reasons, all performance related.

    It all goes back to weight. The flywheel is "rotational mass". Anything in the driveline from the crankshaft to the gears in the transmission to the axles, brake rotors and the wheels is mass that has to be accelerated... and decelerated. Reducing the weight of any of those things reduces "rotational inertia". With less inertia, it takes less power to accelerate those rotating bits, and as Timinator said, it also takes less time for those bits to slow down when power is removed. It is generally accepted that reducing rotating mass is approximately equal to reducing 4x the amount of body weight in the car. So, if you can cut 10 pounds of flywheel weight, it's going to feel like taking 40 pounds off of the rest of the car.

    So, when you're accelerating, some of your power (literally about 15% on the Mirage) goes to just accelerating all of the driveline components. Any reduction in rotational inertia reduces that load on the engine... it's like adding free power! Especially on lightweight and underpowered cars like ours, things like light wheels and a lightweight flywheel are common performance mods. While they don't "add power", they "free up" power. You make your wheels 25% lighter and your flywheel 50% lighter... you're reducing the rotational mass by quite a bit. You might reduce that 15% drivetrain loss to (drumroll....) maybe 12-13%. And you can actually SEE that on a chassis dyno. You're not "making" more power. If you had an engine dyno, it would show the same power. But, because you've reduced the drivetrain inertai, more of that power gets to the wheels, and you can totally see a 2% gain on the dyno from doing nothing more than changing the flywheel.

    It's not night and day, but people pay big bucks to see an extra 10 hp on a 400 hp engine. "Dyno proven to gain 10 hp!" And it's only 2.5%. For us, 2.5% is a much smaller hp number, but it's still 2.5%! And every little bit helps. If I've gained 3% from a header, and another 3-4% from an exhaust, 1% from an intake... and another 2.5% from wheels and a flywheel... that means the car is 10-11% faster! All from simple little bolt-ons. (and yet... 10% faster than slow is still slow... dammit)

    The other thing about a lighter flywheel, even if it didn't have the acceleration benefit, is that it makes it worlds easier to rev-match a downshift. You want to go from 3rd to 2nd? Clutch in, give the throttle the slightest nudge and the revs go right where you want them and you drop into 2nd. And because there's less flywheel mass to engage with the transmission, the clutch engagement is smoother. It's just generally more pleasant and fun to drive a car with a nice light flywheel. (couple that with a nice crisp clutch engagement, and... ooooooh!)

    A lightweight flywheel is just another one of those things that's "greater than the sum of its parts". On paper, it doesn't seem like that big of a deal. But, in practice... especially on a lightweight car with minimal power... it's really nice.

    But, there are downsides. Having less flywheel mass makes the car a little harder to launch from a stop. Most people adapt to this very quickly. You just have to give it a tiny bit more gas and/or slip the clutch a tiny bit more. But, it's certainly easier to bog a launch with a light flywheel. And some cars, particularly those with aftermarket superchargers, will do funky things at idle when the flywheel is too light. The computer tries to adjust the idle speed up a little bit (say you turned on the AC), it's going to overshoot because it's calibrated for the stock engine and it's got a supercharger on it. And then it overcompensates in the other direction and can set up an idle oscillation, or worse yet just stall. Stuff like that. It's not usually a problem on a normally aspirated engine, and usually not something you can't learn to live with even with a modded supercharged engine. (turn the idle speed up a little bit)

    The other thing a lightweight flywheel will sometimes do, especially the aluminum ones, is "ring" at a certain rpm. The aluminum flywheel is sort of bell-shaped, and will resonate and ring at a certain rpm. Stock flywheel is a fat chunk of cast iron and doesn't do that.

    For a gearhead looking for better acceleration or a more sporty feel, the positives far outweigh the negatives. If somebody made a $250-300 8-pound flywheel for the Mirage, I'd already have one!


    Simplify and add lightness.

  2. #12
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    I miss my old miata with a light weight flywheel and stage 2 organic exedy clutch, was super fun for "only" 110hp haha
    2018 mirage ES manual

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        click to view fuel log View my fuel log 2018 Mirage Es 1.2 manual: 41.6 mpg (US) ... 17.7 km/L ... 5.7 L/100 km ... 50.0 mpg (Imp)


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    But yes, if I could find a 20-30% lighter flywheel for $200-300. It would be an amazing investment. I want do the header, and exhaust too
    2018 mirage ES manual

        __________________________________________

        click to view fuel log View my fuel log 2018 Mirage Es 1.2 manual: 41.6 mpg (US) ... 17.7 km/L ... 5.7 L/100 km ... 50.0 mpg (Imp)


  4. #14
    Still Plays With Cars Loren's Avatar
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    Well, still no sign of an aftermarket flywheel for the Mirage. And that's a shame, because I just popped my engine (bent valves from a missed-shift over-rev), and it is now out of the car. Perfect time for a flywheel upgrade.

    I did email Fidanza a while back to ask if they could do anything for the Mirage. Got a simple "we don't currently have anything for that model" kind of response. And I poked around to a couple websites for custom flywheel shops. I figure having one made custom would probably run $6-800. A bit much.

    So, I'm going with plan B. I have a friend with a lathe, and I'm going over there tomorrow. We're going to take some weight off of the stock flywheel.

    And before I put the car back together, I'll try to get some critical dimensions of the stock flywheel. I still think it's possible that a flywheel from another car could be made to work by someone with a little creativity. I mean, like... you get a flywheel and clutch kit from a car with a similar clutch size and layout... and maybe you have the Mirage starter ring gear grafted to it, and maybe have the center holes drilled to fit the crankshaft. It could potentially be done for not a lot of money. Unfortunately, I need to get my car back up and running and won't have time to play with that right now.

    Meanwhile here are some weights to the nearest tenth:

    Flywheel = 15.1 pounds
    Pressure Plate = 6.0 pounds
    Clutch Disk = 1.6 pounds

    The clutch disk is made by Exedy, and has Excedy and Mitsubishi logos on it.

    Given that its fairly light already, I'll be surprised if we get more than 2 pounds off of it without making it iffy. It has the typical big fat inertia ring on the back side. We should be able to remove most of that.
    Simplify and add lightness.

  5. #15
    Moderator Eggman's Avatar
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    Quote Originally Posted by Loren View Post
    The clutch disk is made by Exedy, and has Excedy and Mitsubishi logos on it.
    That's interesting. The factory disc is from Exedy?

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        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 50.2 mpg (US) ... 21.4 km/L ... 4.7 L/100 km ... 60.3 mpg (Imp)


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    Administrator Daox's Avatar
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    I want to say the OE clutch on my 2004 Honda Civic was also Exedy.
    Custom Mirage products: Cruise control kit, Glove box light, MAF sensor housing, Rear sway bar

    Current project: Alternator delete with regen braking modification

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 45.6 mpg (US) ... 19.4 km/L ... 5.2 L/100 km ... 54.8 mpg (Imp)


  7. #17
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    Popped a motor from a money shift? Ouch...time for cams, and full build! Hahaha I was wondering if a older Honda flywheel might work???
    2018 mirage ES manual

        __________________________________________

        click to view fuel log View my fuel log 2018 Mirage Es 1.2 manual: 41.6 mpg (US) ... 17.7 km/L ... 5.7 L/100 km ... 50.0 mpg (Imp)


  8. #18
    Still Plays With Cars Loren's Avatar
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    For anyone who wants to pursue the "what could fit" or "what could be modified to fit" angle, I just took some measurements of my flywheel since it's out of the car.

    First, the flywheel itself weighs 15.1 pounds (and can be easily lightened to 14.3 pounds by having the ring milled off of the engine side... a crafty person with a lathe could probably take another half pound or more off of it without getting too crazy)

    Here's a stock photo of the unmodified flywheel:


    And here's the one I had machined:


    Just for reference, this is what the clutch side looks like:


    CRITICAL DIMENSIONS:

    Well, I'm just guessing as to what's "critical" here, but here are some dimensions. With these dimensions and a stock Pressure Plate in your hand, I think you'd know everything you need to know to compare or create a flywheel.

    And the Mirage pressure plate isn't a requirement. If you had a PP that fit the donor flywheel, as long as it physically fit inside the bell housing and was close enough to the stock position for the throwout bearing position to be adjusted into spec with the clutch cable adjuster... it would work.

    So, if you found a FW that was approximately the same dimensions, and could have the Mirage ring gear fitted to it... you'd be all set!

    RING GEAR:
    OD - 258mm
    ID - 234mm
    121 Teeth

    FACE:
    OD - 251mm

    CENTER HOLE:
    43mm

    CRANKSHAFT INTERFACE:
    Bolts - 6
    Bolt Circle - 68mm Center-to-Center
    Bolt Hole - 11.3mm
    Bolt Size - M10 x 1.0 x 25mm

    DEPTHS:
    Crankshaft to Ring Gear - 38.3mm
    Crankshaft to FW Face - 60.3mm

    PRESSURE PLATE:
    Bolts - 6
    Bolt Circle - 218mm Center-to-Center
    Bolt Size - M6 x 1.0 x 12mm
    Pins - 3
    Pin Diameter - 6mm
    Simplify and add lightness.

  9. The Following 3 Users Say Thank You to Loren For This Useful Post:

    Daox (11-07-2018),Qrush (11-07-2018),Timinator (11-08-2018)

  10. #19
    Administrator Daox's Avatar
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    Nice. So you removed about 1lb from the very outer diameter for the most part? That is the most effective area to remove material due to rotational inertial it creates / removes. It'll be interesting to see if you can feel a difference.
    Custom Mirage products: Cruise control kit, Glove box light, MAF sensor housing, Rear sway bar

    Current project: Alternator delete with regen braking modification

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 45.6 mpg (US) ... 19.4 km/L ... 5.2 L/100 km ... 54.8 mpg (Imp)


  11. #20
    Still Plays With Cars Loren's Avatar
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    The difference will be hard to quantify, as I'm changing 3 things at once that could improve acceleration/response. The flywheel is a little lighter, the engine makes a little more power because it's a 2017 engine, and I'm fitting a smaller battery that's 28 pounds lighter... 28 pounds is over 1% of the weight of the car, and could make as much difference as the flywheel, maybe more.

    So, I'll feel a difference, but I won't be able to say how much of it is the flywheel this time around.


    Simplify and add lightness.

  12. The Following User Says Thank You to Loren For This Useful Post:

    Daox (11-07-2018)

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