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Old 04-21-2019, 02:38 PM   #1
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Lightweight flywheel a bad idea?

Iíve heard a lot of people say that The flywheel is critical to engine balance and replacing it with a lightweight unit without rebalancing the crank is a really bad idea. Is this true, I find it hard to believe everyone is rebalancing their crankshaft when installing one of these.
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Old 04-21-2019, 05:32 PM   #2
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Not true. If the correct flywheel is used, no re-balancing of the crank is necessary.

The stock Boxster flywheel is dual-mass, so I'm not sure what the options are for lightweight flywheels.

If you are only interested in racing, then a light flywheel is a good performance booster, as the engine will rev quicker. However, for regular street driving, it can be a lot more difficult to drive, depending on how much lighter the flywheel is. Often times a much more aggressive clutch is matched with a lighter flywheel, making starting out smoothly even more of a chore.
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Old 04-21-2019, 06:40 PM   #3
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It....

....IS true.
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Old 04-21-2019, 08:36 PM   #4
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Racer boy is on the money here. I installed the AASCO unit. It's GREAT!
I don't find it difficult on the street. However:
The down side is that you lose the damping effect of the dual mass, which has absolutely nothing to do with balancing the motor, and everything to do with absorbing gear noise in thr trans. When my trans is warm, the gears clack just a little.

Many will tell you the flywheel is part of the balanced, rotating mass in the motor: it is not. The rotating assembly is balanced inherently. Some have postulated that at some rpm ranges a harmonic is developed that the dual mass helps to attenuate. This MAY be true. But in all my months of scouring the net looking for actual experience, everything I found was positive. I found one (ONE) confirmed case of a motor failure attributed to a lightweight flywheel. However, this motor also had countless other modifications done to it, and in mind mind, attributing it to the flywheel was his effort at CYA to his customer.
However, I found COUNTLESS other positive experiences with the lightweight flywheel.
And I found lots of people who pretend to know things, because they read something somewhere.

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Old 04-22-2019, 03:07 AM   #5
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Awesome!! Thanks guys.
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Old 04-22-2019, 03:15 AM   #6
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I have the AASCO lightweight flywheel as well in my SPB. No issues so far. If you talk with JG, he thinks this biggest killer of transmissions is the addition of a higher clamping force pressure plate and aggressive clutch plate. He suggested to me to stay with stock with those two items, and I did.
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Old 04-22-2019, 05:24 AM   #7
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I have an AASCO in my SPB and it definitely makes an appreciable difference - as in more than a few tenths. You won’t run near the front without one. Can’t speak to the reliability, but the only place I’ve heard of a LWFW causing problems is on the internet, for whatever that’s worth.
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Old 04-22-2019, 06:44 AM   #8
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In my experience the downsides are gear rattle and stalling. The stalling was experienced in a 993. The software wasn't able to adapt.
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Old 04-22-2019, 11:29 AM   #9
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Quote:
Originally Posted by 356Guy View Post
In my experience the downsides are gear rattle and stalling. The stalling was experienced in a 993. The software wasn't able to adapt.
Perhaps it's because I'm accustomed to lightened flywheels on nearly EVERYTHING I get my hands-on..... but I haven't found the car to be "stall-prone". There seems to be so much torque, it doesn't need the flywheel mass the way an inline-motor does.
But yeah, the gear-rattle is enough that sometimes I'll stick the clutch in at a light.... just to avoid the embarrassment when the guy at the light next to me hears it. hahaha
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Old 04-23-2019, 04:26 AM   #10
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I have an AASCO on the Boxster. One of the issues I had it turns out was the fact I had a Boxster S flywheel on a 3.6 motor. The Boxster S flywheel and I assume other Boxster flywheels have 3 bolts that hold the starter ring on the flywheel. I had one of the bolts back out slowly overtime and take out the Crank Position Sensor. Apparently the 911 flywheel has six bolts. I had mine machined for all six bolts. So - if the flywheel you are getting has only three bolts - I would suggest making sure they are very tight.

The only company that doesn't like lightweight flywheels is LN engineering - they recommend keeping the dual mass.

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Old 04-23-2019, 05:44 AM   #11
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I've had very good success over the years with a -slightly- lightened flywheel for street car use.

Assuming that you start with a heavy steel / iron flywheel, the key is to have a light touch, removing no more than, say 20 to 25% of the weight of the OEM wheel. So, for example, if your OEM flywheel were to weigh, say, 20 pounds, you'd want to remove only around 4 to 5 pounds. This percentage does not sound like much, but it notably improves the ability for the engine to rev quickly, making the car far more fun to drive.

For this reason, I am not a fan of an aftermarket aluminum flywheel when used on a street car. The engine becomes so quick to rev then that rev matching and shifting smoothly becomes much more of a challenge.

Of course, for track use, that's an entirely different set of circumstances, and revving quickly is key. The OP did not mention whether or not the car is intended to be used on the street or on the track, so the above info should be taken with the end use under consideration.

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Old 04-23-2019, 06:11 AM   #12
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I have a hard time imagining that you would even notice 4 pounds revived.

When I changed to the AASCO fw and Sachs clutch kit, I dropped 23 pounds over all. Imagine, 23 pounds on that rotational mass going away! It makes a dramatic difference! But again, this motor has so much torque, stalling is not a problem. And your complaint about rev matching is a temporary one; as muscle memory changes, everything smooths out.

To paraphrase a long time Porsche Racer, tuner, shop owner who I trust very much "it's all good! Only good!"

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Old 04-28-2019, 03:30 PM   #13
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so have you guys that switched to a LWFW also changed to a sprung hub clutch disc?
Pelican recommends it if you have the Aasco.

I was gonna go that way and then ended up staying with the stock dual mass and clutch disc
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