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Old 06-09-2010, 12:49 AM   #1
Doc_Z
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Default Why Dual Mass Flywheels

I've read up a bit on how the DMF's work etc, but I still can't help but wonder WHY now suddenly are engine vibrations a problem?

How come the older generation engines worked perfectly fine with NO CLATTER while using solid mass flywheels.
Seems it's just a money making thing by the agents. I spoke to someone at LUK and they said that for the first few years after a new model is out, the agents hold the rights to the DMF's and they can't supply them to the aftermarket. Only once this licence is released can they supply it to everyone else.

The future is looking bleak cause I see now they are starting to make integrated clutch/pressure/flywheel units. So pretty soon when your clutch goes you're gonna be buying a complete new flywheel/clutch unit!
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Old 06-09-2010, 06:36 AM   #2
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lol they have been using intergrated units for years. they reason the dmf is so that the engine will last longer. they cut back on crank vibration. just the same as the harmonic balancer in the front.
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Old 06-09-2010, 07:34 AM   #3
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Do not know. Did not design the 350Z. Sorry.
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Old 06-09-2010, 08:12 AM   #4
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What older generation engines are you referring to? Nissan's or? Lots of companies use dual mass flywheels as standard. Noise suppression is a huge reason why
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Old 06-09-2010, 08:44 PM   #5
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[quote=Doc_Z;8444035]I've read up a bit on how the DMF's work etc, but I still can't help but wonder WHY now suddenly are engine vibrations a problem


How come the older generation engines worked perfectly fine with NO CLATTER while using solid mass flywheels.





It's not exactly an engine vibration problem that the DMF is used for, rather the effects of HIGH COMPRESSION.
Today nearly all motors are HC & it is not uncommon to see CR's above 12 to 1.

Lets start at the beginning, why do we need a flywheel?
In the late 19th century steam engines were large capacity, slow revving with usually 1 or 2 cyl's & needed a very large flywheel to keep the rotational mass going. Just look at a photo from that era and you will see huge flywheels.

With the birth of the internal combustion engine same problems, slow revving & not many cylinders so still the need for a large flywheel, but not as large as a steam engine.

Move forward to multi cylinder & higher rpm motors & the flywheels are getting smaller & lighter but still a lot heavier than today for a similar capacity motor.

Today the need is for smaller packaging, better fuel consumption & higher power outputs
This is achieved by getting more air & fuel in the cylinder on the induction stroke, COMPRESSING it more, timing the point of explosion more precisely & the result is a much bigger "BANG".
Those bangs at lower rpm,s & wider open throttle positions create the clatter in the drivetrain of a low weight solid flywheel

Same thing when you decelerate. The modern motor cuts fuel & spark for emissions & economy & the very HC's put loads (vibrations) on the drivetrain which the DMF largely absorb

Last edited by Nathan; 06-09-2010 at 08:54 PM.
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Old 06-10-2010, 05:19 AM   #6
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Quote:
Originally Posted by kramykram View Post
lol they have been using intergrated units for years. they reason the dmf is so that the engine will last longer. they cut back on crank vibration. just the same as the harmonic balancer in the front.
You've got to be kidding, right? How would a DMF keep the engine from vibrating??? Totally different than a harmonic damper...

DMF only keeps the engine vibration isolated from the drivetrain... The engine still vibrates, actually more without the drivetrain absorbing it.
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Last edited by djamps; 06-10-2010 at 05:21 AM.
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Old 06-10-2010, 05:26 AM   #7
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Thanks Nathan. What you're saying makes some sense at least.

Is the clatter mainly on 6 cylinder motors?

I'm still unsure why my SR20 with 13:1 CR and a solid 8lb fly has no clatter, but the VQ with what 10.x:1 has the issue.
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Old 06-10-2010, 03:26 PM   #8
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Quote:
Originally Posted by Doc_Z View Post
Thanks Nathan. What you're saying makes some sense at least.

Is the clatter mainly on 6 cylinder motors?

I'm still unsure why my SR20 with 13:1 CR and a solid 8lb fly has no clatter, but the VQ with what 10.x:1 has the issue.
Hi DOC
You make no mention of what vehicle your SR20 motor is fitted too, but the with such a HC & an 8lb flywheel with no clatter I'd almost be certain that it is in a FWD car.
With the compact size of the motor transmission & final drive (2ltr) sharing the same rubber mountings & with large solid driveshafts & CV joints plus all the weight being right over the top of the drive wheels there is a lot less chance of compression to cause clatter & the car itself sort of acts like a flywheel.

I'll give an example of compression.
My son won the Australian production car championship in 2001 in a 2ltr Mitsubishi FTO (FWD). Late in the year he was invited to test a 5ltr V8 Ford Falcon ute (US= pick-up) for a race series that we run hear in Australia.

Well the 1st time he downshifted at high speed he never heel & toe'd correctly to rev match & locked the back wheels & spun out at about 190 kph.

He had only ever raced FWD cars & while he always rev matched on downshifts, the larger capacity RWD vehicle with not much weight over the rear wheels had compession locked the back wheels because he had not rev matched properly.
He was so suprised as he had never had that happen to him in his FWD Honda's & Mitsubishi.

Now if your car is a RWD Iv'e got egg on my face so disregard everything I've said as it's all BS.

Last edited by Nathan; 06-13-2010 at 02:30 PM.
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Old 06-10-2010, 03:26 PM
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350z, case, dual, flywheel, g35, harmonic, infiniti, luk, mass, nissan, noise, rev, slow, solid, transfer, weight



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