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TLDR: Lightweight flywheel + sport clutch disk + harmonically balanced underdrive pulley + headers = significant improvement in acceleration/power
Just wanted to share information and my perception from the seat after my recent upgrades.
My clutch went out recently at 58K, so I decided to replace it myself and wanted to go the lightweight flywheel path. After a bit of research, I went with the kit from Aasco; they balance the flywheel and then balance it with the pressure plate. I’ve ran LWF kits in our previous cars, an FD3S RX7 and E46 M3, so I was aware of the downsides.
Since I was working under the car, I ended up doing a bunch of other “while I’m in here” work, including the RMS and IMS seals, installing a new starter, softest semi-solid trans mount, an RSS Harmonically Damped Underdrive pulley, and a set of Fabspeed sport headers my wife got me for xmas a few years back I never had a chance to install.
These changes, plus the existing mods already on, put my 997.1 3.8 where I wanted it to be in terms of performance. The difference in acceleration is night and day, the car pulls much harder to redline, literally as close to GT3 performance without a 4.0 or upgrading to a GT3. Engine revs effortlessly now, clutch engagement is smooth and less effort to push in, cruising takes very little gas pedal pressure (noticeably less than before). There is another benefit I’m seeing, possibly a result from the reduced drag on the engine and / or the added headers; gas mileage went from 18 mpg to 20.5 mpg avg.
Confirming the downsides: high amount of rattle / noise in neutral with clutch disengaged (with clutch engaged there’s very little noise), driving in the 2k to 2.5k RPM is noisy and some rattle but I don’t normally drive in this range. Overall driving interior noise is increased a bit. To me, I can live with these and it’s totally worth it.
A sidenote on vibration, before the pulley, clutch and flywheel upgrades, I had vibration from 2.8K to 3.5K during normal driving due to the RSS semi-solid engine mounts. After the upgrades, my vibration-o-meter shows this has reduced to between 3K to 3.2K. I can tell there’s actual improvement. The vibration-o-meter I use is my rear-view mirror; I can’t make out cars clearly in those RPM ranges.
PS - The new Bosch starter completely resolved hot start issues!
Hopefully this info on my quest for improvements can help others in a quest for information.
~Attila
Last edited by atihun; 07-19-2023 at 03:27 PM.
Reason: formatting
Just the clutch work was about a full days worth of hours, but ended up being over a few weeks due to the other stuff done and waiting for parts.
I have a set of QuickJacks that made the work very easy. Only challenge was after lowering the transmission with the transmission jack, the transmission itself needs to be lifted off the jack onto the ground to be able to remove it from under the car.
The 'clutch rattle' is noise and vibration transmission from a combination of factors. Reduced flywheel mass by 1/2, removed flex from dual mass, and reduced density of aluminum. The noise starts from the engine power pulses and vibration is actually amplified and transmitted into the transmission gears. The gears will make more noise due to backlash.
I went with a LWFW kit with a spring hub center, that helps with some vibration absorption, and I also added LM MoS2 Anti-Friction Gear Lubricant that helps reduce gear backlash noise.
Notice that the noise really is primarily at idle with foot off the clutch. As you start driving, noise goes diminishes as the engine and transmission increase in speed.
I just did the same lwfw kit and run rss semi solid engine mounts with x51 headers recently as well and everything you describe is very much the same as what I experienced down to the details. To me the best mod I have done to date in terms of driving feel but the down sides of the noise in 2.5k-3k is something I can get used to, maybe many others cannot. Makes the engine feel free and not lethargic .
second favorite is changing the head unit and upgrading the amps. Now I have apple CarPlay and a reverse camera.
my question - I didn’t do the harmonically dampened pulley. Should I do it? Will the engine run smoother?
kwv3’s, all function first parts in the shifter and linkage as well. Quite similar cars were building
bbi dog bones and links to go on next for me. What are your next plans?
I didn’t do the harmonically dampened pulley. Should I do it? Will the engine run smoother?
What are your next plans?
Hey Stephen!
That's awesome to hear. The pulley will help more with the response, unfortunately, I can't say if the engine would be smoother with or without the RSS Pulley. I should have tried out the car after installing the LWFW kit, then added the pulley to see real differences. My money is on the pulley making things run smoother; you should do that experiment.
Next plans are to make a custom intake solution using a 997.2 intake box, sound deadening to reduce the rear tire noise, and some suspension updates (possibly switching to KW Coilovers, Elephant Racing Camber Plates and Adjustable Control Arms And Links). Probably by the time I'm done, I'll be ready for a rebuild to 4L+.
Interesting.... It seemed like the consensus here on Rennlist was to go with OEM clutch and flywheel because the light weight models cause vibration. I could be wrong but I believe there was even a technical discussion that the light weight flywheel throws off the (harmonic?) balance of the engine, which should probably be avoided given the other issues that these engines *could* develop down the road (bore scoring).
This is the exact reason I put this thread on here as I dug through so much information, no real or conclusive evidence. I found one post that referenced one engine where there was a shattered main shaft and the blame was placed on having a LWFW; granted it was from one of the major Porsche engine builders and they swear they'd never install another LWFW. But I found many, many posts like this one: "I heard about horror stories where the lighter flywheel threw off the harmonics on the motor and killed it."
I'm at 60K, so likely I have some level of bore scoring already. I drive my car almost daily and fairly hard. There are more engines on here with scoring, but I didn't see many with LWFW's.
Some things to consider:
I only chose a flywheel that is balanced by the manufacturer - unbalanced would definitely cause havoc on the engine
I chose to use a sprung clutch disk instead of the stock fixed one
I installed a heavier main pulley mainly for the underdrive aspect, the harmonically dampened is bonus and probably would not have replaced it without it
Porsche builds most of their cars with NVH and drivability in mind for their main target demographic (most people would not buy a 911 if it sounded like mine brand new)
The GT3 RS comes with a LWFW - (GT3 RS Factory O.E. Flywheel 11.51 lbs) - (any other 911's?)
I accepted the risks after doing as much research as possible
This is the exact reason I put this thread on here as I dug through so much information, no real or conclusive evidence. I found one post that referenced one engine where there was a shattered main shaft and the blame was placed on having a LWFW; granted it was from one of the major Porsche engine builders and they swear they'd never install another LWFW. But I found many, many posts like this one: "I heard about horror stories where the lighter flywheel threw off the harmonics on the motor and killed it."
I'm at 60K, so likely I have some level of bore scoring already. I drive my car almost daily and fairly hard. There are more engines on here with scoring, but I didn't see many with LWFW's.
Some things to consider:
I only chose a flywheel that is balanced by the manufacturer - unbalanced would definitely cause havoc on the engine
I chose to use a sprung clutch disk instead of the stock fixed one
I installed a heavier main pulley mainly for the underdrive aspect, the harmonically dampened is bonus and probably would not have replaced it without it
Porsche builds most of their cars with NVH and drivability in mind for their main target demographic (most people would not buy a 911 if it sounded like mine brand new)
The GT3 RS comes with a LWFW - (GT3 RS Factory O.E. Flywheel 11.51 lbs) - (any other 911's?)
I accepted the risks after doing as much research as possible
Last year I had the opportunity to drive a 997.2 3.8 S fitted with a single mass, lightweight flywheel. As you and other contributors have said, it’s a gamechanger, so much so, it would be THE first mod I’d undertake if I were to purchase a 997.2.
I’ve owned all the cars listed above (apart from the 991.2 911 R regrettably) and the lightweight single mass flywheel imbued them all with a huge extra dose of character, and the 964 RS especially so.
I’d always read the .2 DI engines didn’t get along with light flywheels?? This is interesting, although I admit I did not like the light flywheels I’ve used on some of my other cars.
07-19-2023, 03:14 PM
WOW! from upgrades
There are more engines on here with scoring, but I didn't see many with LWFW's.
