Lightweight Flywheel

Hi all Just curious for those with a LWFW - do you get extra chatter/noise when pulling away in high gear at low revs? My LWFW appears to have an exhaust type vibration when in the 'wrong gear' Thanks

That might be a harmonic issue that will eventually lead to a broken crankshaft. I'd be willing to bet dollars to doughnuts that you experience some vibrations at certain revs that 'smooth out' above that range regardless of gear...might want to think about going back to a dual mass flywheel.

Quotes source post: 19029901

Yes with a LWFW you will get a lot of transmission noise when you "lug" the engine . Same sound you will get it if the dual mass flywheels locks up/ fails.. You will also get a lot of clatter in the transmission in neutral with the clutch out at idle..

So business as usual and avoid low revs in high gears.....?

Quotes source post: 19029989

Are you willing to change it for less noise and potential for harmonic vibration damage?/

Are you referring to harmonic vibration damage to my ears or the car? I hadn't appreciated that a LWFW actually causes damage.....?

Alfred, what's your goal with adding the LWFW?

Quotes source post: 19030047

Same thing occurs when a dual mass flywheel locks up, it causes noise and looses its ability to dampen harmonic vibrations.. Most people when given the choice will chose to replace the dual mass flywheel when this occurs just for the noise alone even though they could continue to drive the car with the harmonic vibrations undampened and be the same "risk" as a LWFW but without the weight reduction/increased engine braking Harmonic vibration is a very scientific subject and can have very unexpected behaviors , have you ever dealt with harmonic vibrations??

Interesting - I haven't dealt with Harmonic Vibrations before. The car came with a LWFW so just something I am getting used to. I suppose the question is, should I change it to a DMFW? I am getting used to the noise of it, and its fun to drive with the faster changing rev ranges - I just want to check I am not causing damage in high gears at low revs If the above is a normal characteristic then I suppose there is more to get used to with the car....

It came with the car...... I liked driving with it on the test drive - but we didn't sit in traffic when the car was warm so I never noticed the chatter. I am used to it now, but want to check what the best/most suited driving style is for a LWFW

I had a LWFW on my 951 (came with the car), that was my first, and I can say I didn't really like it. I like the feeling of a heavier flywheel much better. $0.02

My 3.6 in my Boxster S has a LWFW . But when the engine was built all the rotating mass was balanced to race spec . I do get gear clatter at idle with foot off the clutch . Other than that I have never noticed any additional noise . The race balance makes a huge difference .

If the noise of a LWFW bothers you, you don't need it also for what it's worth... they aren't really recommended on M96s

I would like to know how it would perform with a fluid dampener on the front.

Quotes source post: 19030431

Unless they are fully balanced during a rebuild. Also you will have gear chatter at idle with clutch out.

It was a CSR build by RPM technik so whilst there is plenty of scaremongering out there, I would be totally surprised if RPM Technik couldn't balance a flywheel.

Quotes source post: 19035431

Agreed.

It's not really about the balance of the flywheel, the flywheel can be in perfect balance and it doesn't make any difference in the "risk" of damage from harmonic vibration, it is the "lack of dampening" that can cause unwanted damage.. All engine designs have harmonic vibrations, the flat six is one is the best ( inline-4 is the worst)...but our factory pistons are only weight matched to within 3 grams, I have seen factory rods from different engines be as much as 15 grams difference and is why the factory only sells the rods in a matched set...( and they are expensive)...When doing a race engine mose shops ballance the rods and pistons to within 1 gram or .5 grams..This reduces harmonic vibrations a lot... All materials/objects have a frequency/Hz at which they resonate...Like a Crystal glass will resonate at 1046.502Hz ( high C note ). If a Soprano singer hits the high C note/1046.502Hz for a period of time, any Crystal glass within range will began to resonate and if sustained will shatter... The combustion on each cylinder causes the crankshaft to flex and causes a vibration...the weight of the pistons and rods also causes a vibration , There are many different harmonic vibrations in an ICE at different frequencies/amplitude and they all will vary in frequency/amplitude with RPM's ....The dual mass flywheels and/or harmonic balancers dampens the amplitude of the harmonic vibrations or change the frequency of the harmonic vibrations so that they do not resonate on a particular part ( crankshaft)... Not using a dual mass flywheel or harmonic balancer does not mean instant failure of our crankshafts, our crankshafts are very high quality ductile steel that is strong but also flexible enough to withstand flexing and vibrations with a very hard thin layer of nitriding on the bearing journals to resist wear. The resonance frequency of our crankshafts can be driven through many many times without damage because the crankshaft is flexable/ductile enough to handle it, but if the resonance frequency is a high enough amplitude and/or is sustained long enough the crankshaft will crack like a Crystal glass when the Opera singer is hitting the high C note .. I didn't want to go too far down the Technical rabbit hole, or give long winded details of my dealings with harmonic vibrations on a high buzzing 12k rpm in-line 4cyl 2.0L 525HP that would snap the flywheel bolts off at 12K rpm because the crankshaft was NOT flexable/ductile enough to absorb the flexing/vibrations of the harmonics...( the crankshaft was actually too strong/stiff to absorb the flexing and harmonic vibrations, so they transmitted to the flywheel bolts and snapped them like glass, even grade 12 loctited and safety wired with 1/2" dial pins inbetween). I even bought one of the $400 Fluidampr's when they first came out in the 80's and destroyed it at 12k rpm in first run.. I just wanted to give some Technical/common sense overview facts of why there is such different opinions on the subject ( this IS a technical forum), It doesn't matter to me which flywheel you use or why. You just sounded a little apprehensive of the LWFW and the noise it causes, justifiably so...

I have a LW flywheel and Sachs clutch that were balanced together by Patrick Racing. When my previous engine let go we found that the dual mass flywheel was in really rough shape and barely hanging together to the point of falling apart when it was removed. The car had a whopping 56k miles. We didn�t want to deal with that and since I was going from a 4.0 back to a 3.6 I wanted to gain back a little performance where I could. Yes it chatters some. I also added a Numeric shifter and Numeric cables and have not yet installed the cable sound isolators so that probably added to the chatter and gearbox whine that comes from the shifter location. I have since added a RSS dampened underdrive pulley and that quieted everything down a lot more than I was expecting. It has gone from a little annoying, which I think the Numeric cables are a key contributor, to barely noticeable under most conditions. Hopefully the sound isolators on the cables do even a little more. I like the LW flywheel quite a lot. There is something about the free revving nature of it. The RSS pulley really helped like it even a little more. If I were to do it again I would just not do the Numeric cables. I am sure the LW flywheel could introduce a resonance that could cause a crankshaft to break and I have seen the pics but it certainly does not seem to happen all that often and does not seem to be something than can even be shown to happen at say X RPM introduces x frequency that shatters the crankshaft. In short, I am not overly concerned with it. A lot of people run LW flywheels and in my mind the biggest consideration is the noise as you are finding out. Think about it this way, the dual mass flywheel is far more likely to go bad than the crankshaft with a LW flywheel and then you introduce the same, or similar, harmonics that the LW flywheel would have introduced as the dual mass may no longer be behaving like a dual mass flywheel.

Quotes source post: 19040938

My LWFW was not very nosy until Numeric Shifter and cables. Same RSS pulley, also RSS mounts. You are right on the money. Had the same kit from Patrick Motorsports Numeric cables added the noise from vibration. It was reduced in half with the hoses installed over cables.

Quotes source post: 19040994

Thanks for confirming that the hoses will help even a little more. You have RSS mounts too? How is it even running with harmonics breaking crankshafts and triggering knock sensors causing a lean condition? I wasn�t brave enough to go RSS mounts so I have the FF mounts ready to go on once I get some time to install them.

Quotes source post: 19030091

Anyone ever seen an M96 crankshaft crack when it has not been in a wreck or has a LWFW installed? Failure analysis is more accurate because hindsight is 20-20... Why gamble if you don't "have to" ? If you were to tell me you needed another 1/10th of a second ET or lap times, and had done everything you could think of reasonably possible, and asked me about installing a LWFW, my answer would be different... But yes I'm old now and I am all about longevity...

Quotes source post: 19041449

Is that a legitimate question or tongue in cheek? I have not seen the failure with or without and am just going by what I read. I assume you have seen this given your history and experience but how often and what kind of failure rate are we looking at? I would assume it must happen even without LW flywheels. Interesting to note that Porsche decided to add the harmonic balancer back in with the 997. I assume there must have been a reason for that and it probably wasn�t due to people fitting LW flywheels. But honestly the m96 is so plagued with potential problems and engineering failures that a broken crankshaft from a LW flywheel probably doesn�t even register in the top 10 most likely reasons these might/can/will fail. My car is on the 3rd engine and is less than 60k miles. I am much more concerned with actual design flaws such as inferior oiling, lokasil, valve guide runners, chipped water pump impellers, intermix, hydraulic locked AOS failures and IMS bearing than the crankshaft shattering. For longevity�s sake we should probably all drive only in warm weather with preheated oil changes done prior to each drive, keeping the RPM sufficiently high enough to allow optimum oil pressure but not too high as to overheat anything and only turn gently and make sure the lateral loads only add up to less than 3 seconds at a time all while maintaining an oil level low enough to prevent frothing but high enough to prevent starvation. Of course only after changing out the water pump, coolant reservoir, spark plugs, coil packs and ethanol approved fuel injectors. This is a good read that is mostly focused on the gt3 engine but remarkable marketing for wanting to get a harmonic damper. They claim sometimes the crank cracks without a LW flywheel. But that may just be anecdotal. Best I can tell this is the precursor to the RSS pulley as they are both in Costa Mesa and the contact info at the bottom even references RSS as a contact, assuming it is the same RSS. My hope is that the puller I have helps to keep my crankshaft in one piece. I know it significantly quieted things down so it is doing something. Interesting article none the less: http://performancedevelopments.com/p...enginefailure/

Quotes source posts: 19041616, 19041616, 19041616

Yes, it was a legitimate question. I have seen cranks crack due to LWFW, but I have not seen one crack when no LWFW was installed, but I didn't know if someone here has seen that before and there could be several hundred people view this so it is possible someone has seen it, and the reason I asked.. I would guess the risk would be about 1% failure rate, which IMHO is way too high for a failure of this importance and the reason I would not suggest doing it, unless it was a very competitive scenario where that slight extra performance would make or break the goal.. I know you had a rod bearing failure even with a Deep Sump and AccuSump, but what other catastrophic failure have you had? And what is your case use? I know you now have a UAOS and a larger IMS bearing so you have eliminated two of the big flaws, the others you mentioned are not on my radar and just a good maintenance regimen should take care of them. I think you are being a bit sarcastic..lol..It seems humans , especially men, tend to go " all-or-nothing".. I think the best advice is drive like it was intended, and use common sense maintenance ... True gearheads instinctively know not to idle an engine for long periods especially in the winter. But other intelligent individuals who are not gearheads need to be taught this, it doesn't just come natural. But the forum does seem to obsess over teaching this.. Yea, that link goes WAY down the Technical rabbit hole on harmonic vibration.. Simply remembering that every material/object has a frequency/kz that it resonates / gets excited at , and an object or material getting excited can be a good thing or a bad thing. Changes in the material or size or shape will change the frequency. Our engines produce harmonic vibrations from everything moving ie. the pistons, rods, crankshaft, timing chains, flywheel, gears, pumps, cams, valves, valve springs, Intermediate shaft, are all producing harmonic vibrations at different frequencies and different amplitudes. They can all coexist and make beautiful music like a well executed Orchestra, or they can resonate/reverberate and do bad things.. If you look around under pretty much any modern vehicle, you are likely to see 1-2 lb weights that are mounted in rubber and bolted to the side of a transmission or rear end. These are to reduce or "tune" harmonic vibrations in the transmission and rear ends..

delete duplicate

Quotes source post: 19041449

Every one I have seen break had a LWFL installed, even Cayman S cranks which are the strongest of all the M96/M97 cranks. That's why we don't recommend running them, but some people still do. We tell those people to have the LWFW static balanced (they are not balanced out of the box regardless of what the manufacturer says) and you need to pair that with a sprung clutch disc and add a harmonic dampening crank pulley. That's going to give you your best chances.

Fair enough, I am surprised to hear the estimation is 1% and that this is the sole cause of those types of failures. Certainly you all would know better than I. I did make it a point to get the flywheel and clutch balanced and added the harmonic balancer to mitigate the risk best I could. I was definitely being sarcastic and mostly joking in previous posts. There is enough fear mongering to go around with the poor m96. It doesn�t always come across well on the internet but I in no way wanted to question the expertise of other far more qualified people than I. I am just happy that there are some people like Skip and Charles willing to try to improve the platform and provide information such as this for all to make their own informed decision. However there are so many things to worry about with these cars and I personally decided the risk was a calculated one that I was comfortable with. It is a fun car and an under appreciated one. For me the LW flywheel adds to the enjoyment. Perhaps I too made the wrong decision. It is a shame that these cars seem to get the short end of the stick when it comes to mods that most other cars can deal with more easily. This is certainly not a hill I would want to die on and there is some good info here for people to make an educated decision, just know the risks. There is plenty that can go wrong even if everything is kept stock which adds to the bad reputation that feels to be a little unwarranted at times. My take to the OP is that the choose is to go back to the dual mass or maybe try to get the harmonic dampener with the hopes that would help some. There is a risk that the flywheel might grenade your engine. Sounds like there is a 1 in 100 chance that will happen which is surprising to me. Good luck!