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      02-17-2015, 02:35 PM   #1
pokeybritches
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Full Review - Bimmerworld's Lightweight Flywheel/Clutch Combo

Bimmerworld's Lightweight Flywheel/Clutch Combo:
- JB Racing Lightweight Flywheel
- Clutchmasters Stage 1 Performance Organic Sprung Hub Clutch

BLUF Ė I love the new connected feel. Iíd trade the performance benefits for less mental stress over engine life. The chatter doesnít bother me. This mod comes with some baggage.

Background
I bought the car in 2006 with 55k miles on it, and I donít think the previous owner knew how to drive it. The wheels were rashed and all out of alignment, it had the stock RFTís, and it generally wasnít set up well. Fast forward to 2014, and it was time to pay the piper for all of those original 55k clutch-burning miles. Iím sure my supercharger and additional 75k ďadult drivenĒ miles didnít help things.

I knew my original clutch was failing when it started slipping between shifts. While upshifting, I wait for the rpm to be matched for the new gear (which sometimes takes foreverrrrrrrrrr). Those rare times when I would perform lightning fast shifts that should bark the tires, the rpm would drag down instead, meaning the clutch was the weak point in the system where that extra kinetic energy was finding its way out.

I went back and forth over this mod for months. The only other mod that I debated about this much was the supercharger, and that was because of the price of entry. I scoured the internet, and the reviews of lightweight flywheels were extremely polarizing. I really wanted a medium weight, solid flywheel to pair with a sprung hub clutch, but I couldnít find anything. What ultimately made me spring for the lightweight flywheel is the fact that I hate spending money on something that gets me exactly what I had before. Upgrade as parts break. I was curious as to how a lightweight flywheel changed the behavior of the car. My mechanic recommended I make the jump to a single mass flywheel, so I did. (He's since passed away, so I guess heís off the hook if the car blows up).

I chose the organic clutch over some of the more extreme materials because I wanted this car to behave like a street car. A common mistake is buying too much clutch. My VF kit only increases torque by 20%, so Bimmerworldís Stage 1 would do. Organic material can survive being overheated (as opposed to Kevlar, which is ruined when itís overheated).

The Good
One of my concerns was that Iíd always heard lightweight flywheels affect drivability. I can officially put that to rest for this specific setup. The feel is absolutely amazing. Itís so easy to rev match. The M54 has a long crankshaft with a lot of inertia. The lightweight flywheel causes revs to fall more quickly, enabling faster shifts. If you donít quite have the rpm matched, the result is less dramatic as the lighter flywheel doesnít have as much rotating mass to translate energy into the drivetrain. In other words, thereís less shock if you screw up, which helps keep the car balanced when driving at the limit.

Direct connection.

No slop.

Both sentences accurately sum up this mod. The factory setup felt like it was connected with a whole bunch of rubber bands with varying elasticity. Combined with the CDV, I was regularly frustrated by rowing through the gears on a stock car. I never felt like shifts were perfect, even when I directed my full attention to them. Now, shifts just happen. Itís like the gearbox has become an extension of the driver.

I donít drive the car often enough to be able to discern a significant difference in performance. The car certainly feels eager. The dyno would probably show it. Independent of feel and chatter (which Iíll get to in a minute), if someone had done this mod to my car without my knowledge, I donít know that I would have known. Since Iím looking for it, yes, it feels faster than it was.

This mod pairs well with a 3.64 final drive in the sense that performance improvements are most apparent when engine rpm is accelerating the fastest, so more shifts = more performance benefits.

The Bad
The question everyone wants answered is, how bad is the chatter? Itís annoying. From inside the car, youíll faintly hear it. Outside the car, it sounds like youíve got a diesel school bus trying to break its way out of your hood. Fortunately it can be silenced by depressing the clutch, and it only occurs on the low end of the idle rpm. At 850+ rpm (like the idle immediately after a cold start), it doesnít happen. I think a raised idle rpm would eliminate the chatter.

Parts of the clutch are under the greatest pressure when the clutch pedal is depressed, so I wouldnít recommend keeping it depressed for long periods of time. As such, if the idle chatter bothers you (Iíd say it would be varying degrees of annoying to 80-90% of everyone here)Ö I wouldnít recommend this if your car sees regular stop and go traffic. Besides, clutch pedal effort increases with the holding capacity, and Iíd say itís about 40% stiffer. So with this mod, your left leg will get tired more quickly, and youíll be tempted to depress the clutch more to quiet the chatter. Therefore, this isnít the best mod for a daily driver unless you get a tune to raise the idle rpm.

FWIW, Iíve driven the car in DC rush hour traffic. It wasnít pleasant, but never found myself cursing my decision to do the mod. I guess you could say Iíve accepted that it comes with the territory. Full disclosure - I hit the gym 7 days a week, so the extra pedal effort doesnít really bother me. It would probably be too much for my girlfriend. If youíre a girly man, youíll hate this mod.

Besides the chatter, thereís an increase in NVH at certain rpm. This is most apparent in two places Ė when lazily accelerating in first or second gear, and when lugging the engine below 2000 rpm (which you shouldnít be doing anyway). The former occurs very briefly (less than a second), almost like an extension of the chatter. The latter is a little more concerning. Heavy throttle below 2000 rpm will cause the car to shudder, and you can feel the vibration in the steering wheel. Whereas before I could get away with accelerating from 1800 rpm in 6th gear, I now have to downshift to avoid the extra vibration. In lower gears, itís not a problem. I honestly donít know if this is just the car talking to me more, as if the strain of heavy throttle and low rpm was always there and now itís just amplifiedÖ or if itís evidence that the lightweight flywheel is allowing more vibration to be translated through the drivetrain. Was the vibration always there, but masked before? Or is there now more strain placed on the car and the vibration is the symptom? Itís probably a combination of both.

Now to my biggest gripe - Iím a prime candidate for an oil pump nut failure. If youíre not familiar with this potentially catastrophic problem on the M54B30 (and the E36 M3), Google it.

The oil pump nut failure occurs in engines that spend a lot of their time at high rpm, and is exacerbated by forced induction. My centrifugal supercharger reaches max boost at redline. I countered this with a 3.64 final drive (stock was a 3.07) so that I could stay in boost and have all the low end torque I need to get off the line, but staying in boost means higher rpm. The lightweight flywheel supposedly increases the likelihood of an oil pump nut failure, and my setup raises the rpm band in which the car regularly operates. It doesnít help that Iím on my original vibration damper, which will soon be replaced. The oil pump nut concerns cause me to limit my max rpm except for special circumstances, so Iím not really getting full use of my centrifugal blower. Thereís always a nagging fear of engine failure in the back of my mind that the oil pump nut could go. At least used M54B30 engines are getting cheap.

OT - This leaves me at a crossroads. An ESS twin screw setup is starting to look appealing; especially when you consider that Iíd be seeing benefits of aftermarket FI cams (next planned mod) throughout the rpm band instead of a brief moment at high rpm. I can get high peak numbers by adding a 10 psi pulley, cams, and WMI to my current setup (Iím guessing $2k installed for the cams, and another $2k for WMI installed and tuned). Then Iíd have a whole bunch of power that Iíd be hesitant to use.

Would I do this mod again? Probably. If the only side effects are what Iíve experienced in terms of chatter and vibration, Iíd definitely do it again. However, I think the vibration is indicative of a greater problem (the extra strain on the driveline), and the vibration is only a symptom. The extra little worrying I do lessens the value of the mod, but unless I start going through engines every couple years, I still think itís worth it. There are plenty of E46ís out there running strong with lightweight flywheels, and I canít find any evidence of a lightweight flywheel being the direct cause of an engine failure on a street driven M54B30 (there is, however, a tracked S54 on these forums whose owner believes the lightweight flywheel caused his engine failure).

Iíd place the concerns with engine longevity in the same category as the S54ís rod bearing and VANOS issues. There are people out there that have been bitten, but as of yet, I havenít been one of them.

Summary
Great mod for a weekend car where you want the connected feeling. Not so good for a daily driver, but it can still be fun depending on your commute.

Pros -
1. Direct feel.
2. A claimed 40% increase in torque holding capacity.
3. Revs rise and fall faster between shifts.
4. More power to the ground.

Cons Ė
1. Vibration = extra strain on the engine and drivetrain.
2. Chatter.
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      02-17-2015, 03:23 PM   #2
Mirko
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Great write up!

I've looked at this mod but never really wanted to follow through with it due to the concerns you've raised and cost.
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      02-17-2015, 03:34 PM   #3
pokeybritches
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I would only do it if I was replacing the clutch anyway, either from wear and tear or preventatively when adding a whole lot of torque (blower). To do it by itself is a little pricey in terms of bang for the buck.
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      03-02-2015, 06:27 PM   #4
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Has anyone tried changing the transmission fluid? UUC suggests a couple of options, depending on climate, and claim that it reduces the rattle and vibration greatly. Of course they sell light weight flywheels and wish to make them more appealing. I ask this as I will be needing a new clutch at some point this year and am concerned about the issues described here.
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      03-02-2015, 06:37 PM   #5
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seems like your experiences, and George's, imply that its not an ideal match for an FI Z4.

I wonder if a CF driveshaft would have similar drawbacks in reliability
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