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Old 01-07-2013, 07:40 AM   #1
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Hmmmm, so many discussions regarding the LWFW.....

In my '90 Carrera 2 I had an RS flywheel which -if I remember correctly- was no dual mass and way lighter, super fun to drive. I guess in those engines it is not a problem.

On the other hand, if someone wants to kill an engine rapidly try a LWFW in an inline 6 like BMW, no bueno!

Not gonna lie, I'd like to use a LWFW in my car but these discussion make me think twice.....
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Old 01-07-2013, 09:07 AM   #2
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A 4-cycle engine only makes power during 1 of it's cycles, until the next ignition during the next power cycle the engine is slowing down. The flywheel mass helps to maintain momentum until the next ignition firing accelerates the crankshaft faster. The flywheel inertia smooths these variations in rotational speed of the crankshaft. The knock sensors can detect excessive variations in this rotational speed & interpret it as "knock" & signal the DME to retard ignition timing. The "low mass" LWFW is not heavy enough to prevent this from occurring.
I believe this is what Jake Raby was alluding to.
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Old 01-07-2013, 10:14 AM   #3
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Thanks Pro , that gives me some information that make sense, instead of vague references.
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Old 01-07-2013, 11:06 AM   #4
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i thought knock sensors were piezo, ie, they actually listen for a knock sound which will trigger them ... ?
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Old 01-07-2013, 12:47 PM   #5
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I had heard of instances where the LWFW can be made to work if you tore the engine down and balanced the crankshaft with the intended fly wheel. I am not sure how you would account for all harmonics this way. Was not aware that the knock sensor used crank speed....wow

Way back when I first got my S, I was I interested in a LWFW to reduce the huge cantilever load on the crankshaft....being worried about the RMS and crank carrier loads ....live and learn
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Old 01-07-2013, 12:48 PM   #6
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Quote:
Originally Posted by The Radium King View Post
i thought knock sensors were piezo, ie, they actually listen for a knock sound which will trigger them ... ?
They detect excessive vibration which is why stiffer than stock mounts can be interpreted as detonation also.
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Old 01-07-2013, 01:37 PM   #7
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sound = vibration. i can't help but think ecu's are sophisticated enough to figure all that out, otherwise that death metal i'm always playing would be messing with my timing. i'm no expert on this, but a quick google tells me that the ecu reads two signals - average and peak, and only declares knock when the difference between the two exceeds a certain threshold in order to ensure that it isn't reacting to background noise. they are also frequency specific; ie. designed to 'hear' knock specifically and not just any bang or rattle. so, you would have to overcome at least two checks before a lightweight flywheel or bad engine mount will read as knock.

further, the guys who would notice the effects of pulled timing the most - cup cars, etc., are all running factory GT3 RS lightweight flywheels and, while i am sure they have go-fast ecu maps, i doubt they run different/more advanced knock protocols.
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