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Old 03-20-2008, 03:26 PM   #1
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Aluminum Flywheel

Hey folks! I have a 94 Civic DX coupe, HX wheels, carbon fiber hood, nothing in the trunk, no A/C (yet) no P/S, manual windows and door locks. I just took the car in to get a VX transmission installed (since my DX trans was trashed from the previous fast and furious owner) that I found at a junkyard, and the guy told me that my flywheel couldn't be machined, too far gone. So, I thought it would be a great time to upgrade to an aluminum flywheel. I'm trying to put my car on a diet to get down to VX weight, which is hard since I have a coupe, but I'm close! Next is the D15Z1 swap, just waiting for my 207K mile D15B7 to go. Here's my reasoning for it, feel free to comment/criticize!

1. Between shifts the aluminum flywheel would allow the RPM's to drop much lower, faster, than with a steel flywheel. That small amount of time would mean nothing after a month, but after several months to a year, there must be some FE benefit.

2. It takes the engine less momentum to turn an aluminum flywheel than a steel flywheel, so the engine will not have to work as hard (provide as much fuel) to propel the car. Since this is rotating mass, this seems to be a huge benefit.

3. The overall weight of the flywheel is 7 lbs, compared to the 16-18 lbs of the stock flywheel. Less overall weight in the vehicle would take less fuel to propel the vehicle. Same as the theory of stripping out the interior of a race car, except in that case, you have more power pushing less weight.

4. The aluminum flywheel has a replaceable steel friction surface, and a replaceable starter ring gear, so this should be the last flywheel I'll have to buy. It was $130 shipped off eBay, and the steel flywheel was $62, only machinable once or twice.
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Old 03-20-2008, 07:58 PM   #2
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as long as it's a recognized name brand company that made it, great. cheap no-name ones have been known to warp or wear prematurely even with the steel inserts.
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Old 03-21-2008, 06:44 AM   #3
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Couldn't say if you'd see any MPG benefit, I wouldn't expect much at least not enough to cover the added expense. The primary benefit though is a little quicker accelleration. The engine will be a little more eager to increase or decrease speed since there is less mass to change speed.

I personally like light flywheel engines. You may want to use a short throw shifter as well as the lighter flywheel will require faster shifts for smooth gear transitions.
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Old 03-21-2008, 09:24 AM   #4
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Steel is used for a reason. Inertia of an object to allow your engine to maintain torque as you drive the little slopes in the road with out constant gas pedal use.
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Old 03-21-2008, 02:10 PM   #5
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I think manufacturers use still because of drivability issues. Steel flywheels provide smoother shifting and a better driving experience. Same reason why they use so much sound deadening material, or excessive slippage in automatic transmissions. I'm trying to reduce the overall weight of the car as well, about 200 pounds, so 10 pounds from the flywheel will help me a lot. I'm trying to make my coupe as light as a VX without sacrificing too many commodoties. And, since I'm adding A/C which weighs 25 pounds, with the new flywheel, it will be like I'm only adding 15 pounds. Well, I'm on my way to pick the car up now, I'll let you folks know how it turned out! Thanks for all of the replies and info!
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Old 03-21-2008, 02:43 PM   #6
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reason #1: steel is much cheaper than aluminum. reason #2: it lasts a lot longer so they can call the car more reliable. it also dampens engine vibrations so they don't have to smooth out the idle the last 5%. it won't give you 1/100 ftlb difference in steady rpm or slow rpm change torque.

if you use heavier pedal, you might get .1 mpg difference. if you barely rev the engine like most people here you may not be able to measure it at all.
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Old 03-21-2008, 03:22 PM   #7
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Well I just got the car back, and I must say, I'm sold on aluminum flywheels. It drives the same, shifting is a little different since the RPM's drop very fast between shifts, and starting out in first is going to take some getting used to. Partly because I'm not used to having a new clutch, and partly because the engine wants to drop the RPM's so quickly that it's a bit more difficult to keep it from stalling. I stalled it right when I pulled out of the shop. All in all, a great purchase, I like the way the engine revs, and drops the RPM's quicker.

But the flywheel was not the biggest difference I noticed, the VX transmission swap was!!

So putting a VX trans on a D15B7 is not a good idea if you have any hope of keeping your current performance or reaching 60mph in under 10 seconds. I'm assuming the VX trans is well suited to the power band of the D15Z1, as was the DX trans to the D15B7. But a VX trans does not belong in a DX coupe. The DX trans moved the car MUCH faster. So fast that I was amazed that 102hp could do so much, compared to my 350hp 80 Camaro. Now, with the VX trans, this thing is a dog. I'm in 4th gear at 50 mph, still under 2300 RPM's. With the DX trans, I'd have to be in 5th just to turn the same RPM's. But, then again, I didn't buy this car to be fast, I bought it to be great on gas, and it looks like it's going to achieve just that extremely well. It really is like night and day. Overall, I'd take the VX trans over the DX trans any day, just because it's going to save me tons at the gas pump, I can already tell from the 10 miles I drove it.
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Old 03-21-2008, 08:57 PM   #8
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Since your gearing is taller now, maybe you could save a few more pounds by getting lower profile tires? That'll reduce the gearing slightly, save some weight, and reduce rolling resistance, too.

I have a light flywheel in both of my cars. The racecar has an 8 pound Fidanza, which I like a lot. My Laser has a 12 pound chromoly flywheel.
I got the light flywheel to improve FE since the car has to accellerate from a stop many times each day on my commute.

With a light flywheel I found I can shift gears earlier, keep the rpms down and still accellerate at a decent rate. A light flywheel makes more of a difference in lower gears, so it helps improve FE when driving around town, or anytime you have to accellerate at low speeds. It doesn't make much difference in top gear on a freeway, or anytime the cars speed is held steady.

The issue of loosing torque with a light flywheel is just a myth. The motor makes torque, not the flywheel.
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Old 03-21-2008, 09:24 PM   #9
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Here's a good link describing how a light flywheel behaves.
www.pumaracing.co.uk/FLYWHEEL.htm
Thanks to whoever originally posted it here, very nice.
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