Considering going back to stock flywheel

Hey guys, Don't want to start a debate about light weight flywheels and such just wanting some opinions. Previous owner installed a LWFW with sprung clutch disk and cargraphic underdrive pulley, I stuck with it when I got a new clutch. At the point where I have collected all the parts to go back to stock and will more than likely pull the trigger soon. For a few reasons: Car doesn't see the track, street driving becomes laborious and the potential of engine damage due to no vibrational dampening etc etc. Few questions, has anyone gone back to stock dual mass and missed the performance of the single mass? Anyone gone back because of potential engine damage? It always just seems to be in the back of my mind... I do feel like it is missing torque down low when taking off too, anyone experience that? Would it be recommended to go back to the stock pulley in place of the cargraphic one too? Thanks!

I went back to the standard pulley - I haven't been doing anywhere near enough driving events to make the underdrive pulley worth having, and while the additional freed-up HP is nice, my car seems happier with the alternator running as designed via the stock pulley. It sounds like we're in the same boat as far as having a 996 that sees more street use than track use - and I concur that going with a standard dual-mass flywheel and the OEM pulley makes sense for this use case. I don't know how many cars have actually been damaged by the lack of damping from a LWFW, but I recall Jake's postings about a guy who went through multiple (two? three) crankshafts before switching back to the dual-mass flywheel. My 996 has been quite reliable so far; intentionally making changes that might reduce the car's reliability isn't where I want to go.

That�s my feeling too, reliability vs performance. Not sure if I�ll miss the instant acceleration of the LWFW but I won't miss the gearbox chatter and un smooth driving. Did you miss the performance? To be honest I�ve never driven another 996 with a standard flywheel so I have no idea what it will be like! Will I get some torque back at the lower end? One thing I don't like that much is that there doesn't feel like there is much "pull" when taking off, if that makes sense?

I haven't ever had a LWFW in my 996, but when I went from a LWFW to a dual-mass unit in my 5-speed Korean "sporty sedan," the difference was obvious, and in a good way...shifts were once again smooth and un-hurried since engine RPM no longer dropped precipitously during shifts. I've pretty much decided that future AX and other stuff will be done in the Corvette. While I don't really want to beat on either car, hammering the one for which rebuilt engines start at about $1K makes fiscal sense.

Yeah I don't think I enjoy it anymore, time to go back to stock!

I briefly used the single mass flywheel combo in my old (1995) 993 I went back because I put it up for sale and didn,t want to have to make excuses for trans rattle and occasional stall. I hardly noticed any difference. I,d be interested in your underdrive pulley for my current 986 S. except you are on the other side of the world.

Sure, soon as its out it will be on the market. Its a nice unit are cargraphic stuff is the best IMO. Ill keep everyone posted! Time to get some quotes on installation

Good post for me to watch, about to install LWFW and Underdrive pulley

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There is and has been a big debate about this but seems like there isn't a consistent behaviour from the majority of the users regarding reliability. Also Porsche has the Clubsport 996 model which did come with a lightened flywheel from the factory if that says anything, granted it was on a different motor but general concepts still the same.

I would assume - but have no evidence to support it - that an engine destined to be used with a lighter-weight flywheel would have more balance work done on it. The dual-mass flywheel is perfect for the "close enough" you get with engines produced quickly in large numbers.

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Bingo.

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The amount of torque the engine produces doesn't change with a change in flywheel. What you get back with the stock flywheel -- which BTW isn't that heavy (or large in diameter either) compared to other flywheels -- is the kinetic energy the flywheel has courtesy of the engine. It takes X amount of effort to get the car moving and because of the flywheel you can use less RPMs to supply the required amount of energy to get the car moving as the flywheel gives up its kinetic energy. Even with the 2.7l engine and its 192ft lbs of torque in my base Boxster coupled with the stock flywheel it takes just 1K RPMs and smooth clutch pedal action -- hey it is the price you gotta pay if you want the manual shifting experience -- the car moves off a stop with minimal clutch slippage. And the car moves off from stop smartly too so one doesn't have to fear a blast from a horn by an impatient bozo from somewhere behind. The same technique works with my Turbo, too. This helps to explain how I managed nearly 300K miles on the original clutch in the Boxster and at 120K miles the Turbo clutch showed no measurable wear. Now with just over 141K miles I expect the Turbo clutch to last at least as long as the Boxster clutch. As for your expressed desire for reliability over performance (actually you get the best/balanced best of both worlds with the stock flywheel) then you should reconsider your decision to run an under drive crankshaft pulley. This slows down the speed water pump spins which means less cooling coolant is circulated past a given point. While you may think this doesn't matter, how fast the coolant flows, it can be critical. You can see what the water pump is up against, so to speak, but putting a pan of water on the stove and heating it up. As the water heats up small bubbles form on the bottom of the pan. If you gently move the pan in a circular fashion to cause the water in the pan to circulate in the pan the water will dislodge these bubbles. Thus the water then can make contact againi with the surface of the pan. As the pan gets hotter, the water gets hotter, and the bubbles grow in size and their dislodging becomes harder. You have to move the pan about with more vigor to dislodge the bubbles. The same thing happens in the cooling system. The water pump's speed is intended to circulate coolant with enough velocity, force, to dislodge, or better yet prevent the formation of, any bubbles (steam pockets) forming. This is critical enough under light throttle light load but critical doesn't begin to cover it when the engine is working hard. Coolant temperature can climb to -- my observation -- 226F and that's hot. The amount of heat being transmitted from the aluminum to the coolant is tremendous and even a momentary formation of a steam pocket can spell trouble even doom. Once a steam pocket forms it blocks coolant flow over the area it covers. Localized overheating results and the heads (which is where a fair amount of heat is transmitted to the coolant) can develop cracks. The prevention of the formation of steam pockets is why it is very important a cooling system be pressure tight. It is pressure and pressure alone that raises the boiling point of the coolant above 212F. And this is why even though for instance while my Boxster's engine has spent upon occasion hours with its coolant at 226F it has not suffered one bit from this elevated coolant temperature.

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Possibly. Good theory either way whether true or not. I know some assembly by some manufacturers is automated and has computer controlled balancing machines as part of the manufacturing process. I'm not sure if Porsche is one of those.

Thanks guys, I guess out comes the LWFW and pulley and in go the standard parts. Underdriving components just sounds like trouble so for my application it will come out as well.

Our charging system was not very well designed to begin with (bad cables, low alternator output due to heat compensation, voltage loss on long cables between the alternator and the battery, etc.). I think you're very wise to revert back to the stock pulley.

I can state with certainty that I was seeing more voltage fluctuation with the underdrive pulley, to that point that sometimes - especially at stop lights - the voltage was dipping low enough to trigger ABS/PSM warnings. Since reverting to the stock pulley (and making no other changes at the same time) that symptom has disappeared. I did not see any cooling issues running the underdrive pulley, nor any issues with the power steering pump.

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I'm currently not experiencing any cooling issues but I am experiencing a hot start issue where the voltage drops when I try to start the car and I have to press the gas for it to kick over. Might or might not be related to the pulley. Might be the starter or cable.

The hard-to-turn-over-when-hot issue is generally due to the starter cable degrading (or maybe a bad starter) - I have the same issue (and there was no overlap between dumping the UD pulley and the development of the hot start problem)...

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I thought the issue would be unrelated to the UD Pulley. Have to figure out if its the cable or the starter. I actually hope its the starter, looks much less complicated to change over! Does the bumper and exhaust parts need to come off to replace the pulley?

Our charging system is not very well designed to begin with (bad cables, power loss on long cables between alternator and battery, low alternator output voltage due to wrong heat compensation) so I highly recommend not make it worse by using the under drive pulley. If your system isn't in its best shape to begin with, the under drive pulley can only exacerbate its problems. Agreed your hot start issue is likely the starter or the y-cable. Replacing the y-cable is no longer difficult if you use the hot water trick to remove the plastic cover attached to the new cable. Search here on Rennlist for the y-cable trick. Without that trick, that cover requires the a/c compressor to be unbolted to snake the cable in. Btw, you can use a voltage drop test to verify if the y-cable is the issue.

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The hot start issue is probably starter. Mine was about to go. Agree on sticking with stock clutch/flywheel. Don't mess with it. Remember that it's a holistic system, for all its weaknesses and tested as such. You change one parameter and the weakness is either revealed or moves down the chain to a component that cannot bear the added stresses.

I'm hoping it's the starter! With the voltage drop test is it a test to see what the voltage is at the starter compared to what it is at the alternator? Agree on the view that the system should be treated with a holistic approach and parameters shouldnt be changed. Hence reverting back to DM flywheel and standard pulley asap. Still waiting on a quote from the dealership

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Close. The voltage drop test is to test the voltage between the output of the alternator (back of the alternator) and the engine "+" jump start terminal next to the a/c comressor when about 60A is going through that y-cable (e.g., when a/c and low beam are ON). You should see ~0.1v or less with a healthy cable. What does your voltmeter read at idlng when engine is hot and when a/c and low beam are ON? If it's 13.5v or higher, your cable is likely fine.

Thanks Ashai, I'll have to measure it over the weekend What's the best way to measure the alternator voltage? I can't think of a way to get behind it to the output?

To access the output terminal at the back of the alternator, I just bend a stiff INSULATED metal wire into a j hook. Remove 1/4" of the insulation and use the tip to poke aroumd the back of the altermator. See post #15 here http://www.renntech.org/forums/topic...on#entry241245 image.jpeg

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Perfect! Thanks

Keep in mind engine needs to be hot and idling. a/c and low beam need to be ON to generate enough current when measuring.

Sounds good ill follow that procedure and report back thanks

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Several years now with an underdrive pulley and a 7 lb. battery, no issues whatsoever with PSM/ABS or any other idiot lights flickering. No cooling issues, either. Both autocrossing and more than a handful of times in stop-and-go, crawl-speed L.A. traffic. About to install a lwfw (and Wavetrac diff) myself so this thread's also caught my attention.

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Similiar experience myself. I've been running the Mantis one for a few years now. I recently switched to Schnell's old one because it had the speed holes and still no issues in all sorts of conditions including 35deg temps.

I think there are some minor electrical gremlins in the 996, but after owning a grey market Jag, they're NOTHING...

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I think your old Jag is pretty close to the 05 Rover HSE I didn't even keep for a year. Example #4345. The wipers wouldn't work so I would pull over turn off car and turn back on then they would work. That thing reminded me of being a boat owner, the best day was selling it. -Jason

Okay! Finally got to do that voltage drop test the results were not pretty... So with: - Radio on - Low beams on - A/C on full Reading at the back of the alternator: 13.45 volts Reading at the jump block: 12.83 volts The wire is cooked isn't it

The y cable is shot for sure. The alternator doesn't look too good either. It should be closer to 14v

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Even with all the accessories on it? Ah I also have a cargraphic under drive pulley im guessing im loosing a bit of voltage from that too

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The 13.45v makes sense with an under drive pulley but that y-cable is still bad.

Btw, forgot to mention some important numbers. To charge the battery properly, you need 13.5v to 14.5v. The normal voltage loss on the long cables from the alternator all the way to the battery will be about 0.3v or so. That means the alternator will need to generate at least 13.8v. Otherwise your battery will not be charging. So yeah if you keep the under drive pulley, just avoid idling your engine

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That might explain why I need to use my battery maintainer so often! I always try to keep it topped up, actually its charging right now Thanks!

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Combined with a bad y-cable...pretty much hopeless

Yepp! Sad times haha

Good times today as my new OEM flywheel arrived! Actually didn't realise how damn heavy it is!! Wonder what my current one weighs!

So car is at the dealership at the moment, list of jobs is growing... So far they have discovered that the independent I used (and I'll never go back to) crossthreaded my gearbox bolts and did them up with a rattle gun... So the thread specialist is coming tomorrow to fix it. As well as now needing a new coolant reservoir, y cable and possibly a new slave cylinder, woo. Ahh 12 year old sports car fun!! Oh well ill have it back soon anyway

Hey all! Thought i'd give an update after 3 months I have my car back! Booked it in for some minor body work which took most of the time. Anyway starting problem is fixed the cable was indeed toast, starts strongly now As for the flywheel my car does feel significantly smoother but "slower" on the plus side it is my easier and smoother to drive. The power is still there it just takes some time to get up and boogie... Highly recommend the mod if you don't mind the challenge, although I think it munched up my throw out bearing!

I have 2500 miles on my new lightweight flywheel set-up. If I had to do it all over again, I don't think I would have done it, but it is in. The transmission rattle drives me crazy, which is a short trip anyway. It sounds like a diesel engine at a stop light

Thats something I definitely don't miss! The performance on the other had, I'm going to miss that

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Sounds like what we need is a light weight dual mass flywheel to eliminate the tranny rattle but still allows the engine to rev up quickly. I too have a LMFW and hate it. I'll do my best to wear out the clutch so that I can go back to the dualmass flywheel and have the engine purr like a kitten, not rattle like a diesel.

Lightened DMF now that would be awesome!! Free up power but still retain the dampening

I saw somewhere there was an oil manufacturer that advertised a gear lube that reduces rattle. Has anyone seen it? It sounded like hocus pocus to me. Thinking it was Royal purple

Think about what your knock sensors are hearing.

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Which Flywheel do you have? The only one I've heard much about, from RPM technik in the UK, is available with and without spring-loaded friction plates. The friction plates apparently reduce "chatter", so I'm wondering if your flywheel also has such friction plates ...

I dont think I've ever seen a flywheel with Springs on it, it's usually the clutch friction disk that has those. There are many manufacturers of LWFWs: - aasco - cargraphic - genuine Porsche

I have the Aasco LWFW and ClutchMasters 450 Sprung clutch. Like many did a ton of research and was on the fence about this big time, especially after reading into the crank issues, Raby and others feedback, etc. The Cantrell and many other 996/997 GT3 Cup Cars all consistently use the Aasco LWFW as well. Most also use the Sachs High Performance Sprung Clutch. I absolutely love mine. Its amazing how fast the car revs at the track. Blipping/HT was immediately easier and led to faster times. For street driving, I stall the car occasionally especially in reverse but thats about it. No other issues. Idle is fine. The clutch pedal is similar to stock, somewhat heavier but easier to gauge when it engages after removing the helper spring. It does sound like a box of rocks but its also a track only car (16+ events per year) If this was a DD with limited track use, I'd recommend against it.

I'd definitely concur with that, performance was excellent. Daily driving isn't the easiest but I got used to it. I'd recommend it if there are no more mods left on your list but IMO this one comes last if your cars driven daily.

I have Assoc flywheel and Sachs sprung disc. I have a Evoms stage IV tune with 5k launch control, before flywheel, I thought the 5k was too much, but now with LWFW and 12" rear tires, the car needs the 5k to launch strong.

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Did you conclude that there are no crankshaft issues (or other engine damage issues) with your setup? And why do you recommend against it on the street? Just the sound, assuming one can live with stalling from time to time? Is the sound just when idling, or maybe also at parallel-parking speeds, or ... ? Actually, that's another question. If it's easy to stall, I bet parallel parking and parking in tight spots must be a huge pain, no? Finally, I'm curious - why ClutchMasters instead of Sachs? Thanks!

1- A sprung disc just reduces the racket that the set up makes... 2- The detrimental effects are still there. 3- The sprung disc will see decreased longevity due to the operation of the single mass flywheel. 4- The engine will still see retarded ignition timing events compared to a dual mass unit. I have seen as much as 12* of retard above 5,252 RPM back to back in a direct study. That was on the road, on the dyno it was more like 17*. Grab a scan tool and do a back to back test, I found this in 2007 and I have seen it over and over again since then. 5- The M97/ M97 isn't a cup car or GT3. Those engines have also had TSBs released by Porsche stating that a single mass flywheel should not be used. I'll look for that TSB tomorrow. There's not many things that you can bolt onto one of these engines that's a worse idea than a LWFW... Well, except, maybe a turbo. Some people like them because they are cheaper than a dual mass...

I did a ton of research and decided to stick with the DMF.

The ignition timing issue just may be what is happening with my car. At 2900-3100 rpm, something happens with the revs that was not there before the installation of LWFW, there is a"bump" in rpms. I thought maybe the tune had a hiccup, but after a little bit of research, I was leaning towards a timing issue. Thoughts?

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if you replace the flywheel with a dual mass, I have a hundred dollar bill that says that issue will go away. That RPM is the first point where harmonics increase in the rev range, and I've seen this exact same thing in the past with a single mass LWFW. The issue isn't that the flywheel is lighter, it's the fat that the dampening mass is eliminated.

OK, mind made up on this one. Shame, I'll replace the RMS soon, so the tranny will come out, and there's a bit of chuntering at parking speeds, so I wouldn't be surprised if the DMFW will soon need replacing. So what could be better than something cheaper that makes the car livelier and better accelerating? Seemed too good to be true. Apparently is.

The cheaper and livelier parts make it easy to hook owners with this... Too many don't research it first.

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This may fit and will save you $600 if it fits: https://rennlist.com/forums/parts-ma...ring-used.html Check compatibility: http://986forum.com/forums/performan...fferences.html

I have a used dual mass flywheel in decent shape. I replaced it just because but it still springs and I can verify that it's within spec if you're interested. Also have a new, uninstalled pilot bearing.

So yet another non-free lunch. Other candidates? One could reportedly also get a similar boost in performance with a 200 cell X-pipe cat & muffler system. And it too sounds a bit like a free lunch: more power, less weight, better sound. What�s not to like? Actually, I�m pretty sure there is more top end power with a good system. Never mentioned � except in a few places on this forum � are claims/rumors of less torque at low revs with an X-pipe. A bit less might be an acceptable trade-off. But I�d worry the throttle response around 3-4000 rpm goes too �