Project BMW M3 Part 3: Clutch and flywheel upgrade

In the first part of this project series we learned of my experiences with a slipping clutch--a problem I was having after only a couple of baseline quarter-mile test runs. The second write-up included testing with different software and intake systems, which allowed the car to make more power without putting much more stress on the drivetrain.

Before going any further, I wanted to tackle the clutch issue. The car needed a clutch kit with more clamping force, one that wouldn't get "greasy" after a few jolts off the line. For this the '95 BMW M3 got the Active Autowerke treatment.

Over the past several years, brothers Karl and Mike Hugh of Active Autowerke have been putting serious power to the ground with their turbo M3s. According to Active, its clutch kits tested up to 500 hp, so I figured the clamping force would more than suffice.

The clutch kit consists of a high-performance pressure plate, a composite disc and a release bearing. It doesn't sound complicated, but the labor involved in a clutch replacement is quite extensive, requiring removal of the transmission housing to expose the dual-mass flywheel. If I were ever to install a lightened single-mass flywheel, now would be the time. Fortunately, Active sent its new Generation3 single-mass aluminum flywheel along with the clutch kit. Having previous experience with Active Autowerke flywheels, I knew I wouldn't go wrong in using its latest version. The flywheels in Active's turbocharged M3s have to withstand a tremendous amount of torque.

Again, as I'm a fanatic about weight reduction, the flywheel was put on a scale; it weighed in at only 12 lb (11 lb without the bolts) compared to 26 lb for the stock dual-mass flywheels on the '95 M3s. At half the weight, the Active flywheel was sure to give the car a new feel and better throttle response.

During the last three years, Active Autowerke has worked diligently on making sure its flywheels will handle 500 hp. I recall having its first-generation flywheel (it weighed 10.5 lb including bolts) on my previous '97 M3 and not experiencing any problems whatsoever. Since then, Active's flywheels have evolved into a third-generation package, resulting in a little added weight. "We were finding that the thinner flywheels were flexing with the turbo pressure plates and causing the disc to only make a 50-percent contact with the flywheel face and pressure plate. That is why our flywheels went from 10.5 lb to 12 lb," said Karl.

The flywheel is made of T6061-T6 aircraft-quality aluminum and comes with a steel face of a high carbon type, heat-treated for maximum wear. The dowel pins, unlike with some other flywheels, are secured from behind after being pressed in rather than simply pressed in. "We've seen other [pins] fly out and destroy the transmission bell housing!" Active Autowerke believes its own flywheels are in a different class.

The previous owner of my '95 M3 had installed a short-shift kit I didn't care too much for. It was as if the "H" pattern of the gear selector was moved down, rather than being shortened, and it no longer fit perfectly in the center. To give me an idea of what a good short-shift kit should be, B&M sent me its latest Short Shift Kit for the E36 M3. B&M's short shifters have a reputation that is second to none; every tuner I asked about B&M had the same thing to say: "Yep, they make some real good stuff!"

These short shifters are CNC machined from 303 stainless steel and 6061-T6 aluminum and are backed by a limited lifetime warranty.

Without a hoist in my garage, I wasn't going to try this entire installation myself. I left the car in the hands of evosport's tech facility in Huntington Beach, Calif. evosport, a BMW, Mercedes-Benz and Ferrari tuner, has experience racing and tuning various BMW M3s. Since Project M3 will be experiencing many track days in the near future, a tuner with racing experience was desired, and evosport thankfully stepped up to the task. The company's serious approach and passion became evident upon my first glimpse of its multi-hoist garage, which also houses a Dynojet dynamometer used for extensive testing of its products--and they do test everything.

When the car rolled into evosport's tech center, we took the box of new stuff out of the trunk and inspected Active's clutch kit. One of the workers noticed that the pressure plate looked almost identical to the stock unit, with the exception of it being painted red. When asked about this, Active's Mike Hugh was prepared to answer: "The pressure plate is a high-performance unit sent to us from Germany, which we then send out to our guy who re-calibrates them to hold more power,"--and hold more power they do!

Just for kicks, Vadim Fedorovsky of evosport and I took the new and used pressure plates to George Kohler of McLeod Clutches in Orange County to have them compared. The stock Sachs pressure plate tested 1,669 lb of clamping force--not bad for a used O.E. clutch. Next up was the Active high-performance unit--2,608 lb of clamping force. George's eyes got real big: "Now that's a lot of clutch!"

"So you think it will handle up to 400-plus hp?" I asked him. George didn't even think twice, "Yep! Shouldn't be a problem." Needless to say, I gave the okay to have the clutch installed.

Later in the week, I went back to pick up my car. The technician brought the M3 out and we let it warm up. The lightweight flywheel's "clattering" noise was already apparent, but it wasn't annoying. I got inside and started playing with the throttle. Blipping the throttle in neutral made it obvious this car was revving up significantly more quickly. I pressed down on the clutch ("Hey, not as stiff as I thought; feels good!"), put it in first gear ("Nice!") and let the clutch back out ("Whoa..."), discovering that the new pressure plate released much more suddenly than the stock unit.

If you plan to purchase one of these clutch packages, just remember to press the clutch pedal all the way to the floor to fully disengage it. Its quick release won't let you shift unless you really step on it. In any case, the pedal has a good, solid feel to it and yet is not too harsh. And if you desire a more aggressive clutch setup, Active Autowerke has a 6-puck clutch disc, which handles even greater power but is designed primarily for racing applications.

The B&M short shifter felt great from my first shift into second gear. Every gear choice felt smooth, leaving me confident that a costly miss-shift wasn't peeking its ugly head around the corner. I gave the M3 my first full-throttle rip and realized a pleasant zinging noise coming from the flywheel as the revs climbed. It sounded like a quiet supercharger! In the midrange it began to spool up faster, and then suddenly the rpm shot to redline with anger. I pressed the clutch pedal and watched the tach needle quickly drop back down again. Grinning from ear to ear, I looked over to Vadim, "This feels much more like a race car now!" The throttle response was very impressive and, as a result of the quicker revs, heel-and-toe downshifts were a piece of cake.

But, another noticeable difference was the loss of some low-end torque. The car seemed to rev more quickly but not until higher up in the rev range. Off the line, the car wouldn't pull like it used to when I dumped the clutch at 3500 rpm. The inertia generated from the heavier stock flywheel couldn't be reproduced with this lightweight unit for an out-of-the-hole launch. But, once the revs climbed, the needle was noticeably quicker, at least in the first few gears.

There's a rule of thumb recited by many M3 owners: The acceleration gains from a lightweight flywheel are equivalent to the acceleration gains an M3 will get from a 250 to 350-lb vehicular weight reduction in 1st gear, 100 lb in second and minimal gains in acceleration from third gear on up.

To see how close these numbers were, Project M3 was sent to our dyno man, Dominic Conti at the McMullen Argus Tech Center. I hypothesized that if there were to be any changes in acceleration, the rear-wheel horsepower and torque figures would show it. The M3 was loaded on the Dynojet 248C and a few first-, second- and third-gear runs were performed. Keep in mind that the intake temperatures were 15-18*F warmer this time because of the climate change, giving a small advantage to our baseline flywheel runs performed weeks earlier.

In first gear, sure enough, there was a loss of torque down low. The new 12-lb zinger gave the M3 a maximum loss of 8.2 lb-ft of torque and 5.7 bhp at 3660 rpm. The gap between the two curves steadily decreased to zero until they equaled at 5500 rpm. At this rev range the Active flywheel took over, with a maximum gain of 8.5 lb-ft of torque and 10.8 bhp at 6700 rpm. In addition, the car revved 120 rpm more than it did in the baseline run.

So, which would you choose--an upgrade that makes your car quicker above or below 5500 rpm? Before we answer this, let's take a look at second gear. Surprisingly, up until 4700 rpm, the lightened flywheel maintained torque with only a maximum loss of 2.4 lb-ft and 1.9 bhp at 4000 rpm to the stock flywheel. After 4700 rpm, the flywheel showed its advantage with a constant gain to redline, revealing a maximum gain of 4.4 lb-ft of torque at 5500 rpm and 4.7 bhp at 6500 rpm. Third gear runs were tested but yielded no significant gains or losses.

Whether the equivalent weight-loss theory stated previously was proven I am uncertain, but it did not seem too far off. In any case, it's safe to say the Active lightweight flywheel has both advantages and disadvantages over the stock unit.

Disadvantages: First, Active's flywheel did make some clattering noise while idling or under load at very low rpm, and especially if the A/C was turned on. Accelerate from 1500 rpm in fifth gear (something I do not recommend), and you'll really see what I mean by "clatter"! The single-mass lightweight flywheel cannot absorb torsional vibration from the crankshaft as effectively as the dual-mass stock unit (for this reason it is not recommended to use a flywheel and underdrive pulley upgrade together). Second, you will lose some low-end torque--especially off the line--as our dyno charts have shown. And last, the boys in Munich chose a heavier, dual-mass flywheel also to make it a bit easier to drive smoothly around town.

Advantages: First, the loss in low-end torque and horsepower is significantly made up in the upper rev range. Second, revs go up and down quickly, aiding in a quicker and easier heel-and-toe downshift. Third, there's a 14-lb loss in your vehicle's weight, which was more weight loss than the car had with the new exhaust. Fourth, the throttle response is greatly improved over stock. Finally, I really like that little "zing" noise!

Which should you choose? Consider in round one (first gear) that we have somewhat of a tie, assuming we want both low- and high-end torque--we win some and we lose some. But, that 10.8-bhp gain at 6700 rpm does sound appealing, especially knowing the difference would be a bit larger had there been more rpm available from the M3. In round two (second gear), the Active Autowerke aluminum flywheel made up its low-end torque loss and still bounced back with more wheel horsepower to play with. And what do you think would have happened had we tested this flywheel under our previous, cooler baseline conditions? Would it be safe to say 1 or 2 more hp?

I'm going to stay with the Active Autowerke flywheel, thanks.

Author's notes: In Part 2 of this project series, an Active Autowerke/ECIS intake system--comprised of a larger air mass meter, conical intake, heat shield, 21.5-lb injectors and custom chip--and Active Autowerke exhaust setup were tested. Maximum peak gains and losses over stock failed to get mentioned. At 5350 rpm, Project M3 peaked with 18.7 hp and 18.4 lb-ft gains at the rear wheels over stock.

In part 2 of the project, this setup also achieved an additional 10.8 hp (not 10.8 rpm as mentioned) peak gain at the wheels over the similar AA/ECIS setup with stock 17-lb injectors at 6900 rpm.

evosport inc.
(714) 731-6040
Order: (888) 520-9971
Fax: (888) 520-9972
E-mail: info@evosport.com
www.evosport.com

Active Autowerke
9940 S.W. 168th Terrace
Miami, Florida 33157
(305) 233-9300
Fax: (305) 253-8921
www.activeautowerke.com

B&M Racing and Performance Products LLC
9142 Independence Ave.
Chatsworth, CA 91311
(818) 882-6422
www.bmracing.com