Project CrossTime Gets A Much Needed Upgrade From SPEC Clutch

When my buddy and I bought the Project CrossTime Miata a year ago knowing it had 187,000 miles on the odometer, we knew there were going to be some things that would give up the ghost eventually. We immediately had to replace the slave cylinder to even get it to move. Surprisingly, other than that, this has been one rock-solid little roadster. Of course, we have been changing out parts along the way for the project build, but nothing in the drivetrain department.

During my last session of the final event of the season, I had a good guess as to which part was going to give up first. The car started “chunking” into gear at speed on almost every shift. It seems the clutch was too tired to do its job anymore. Before I really hurt it, I brought it in early and called it a season. It was a successful season for me as a newbie racer and the little $1,000-Miata-that-could. I learned a lot about myself, the car, and what we could do together.

My final event of the season would be the last time CrossTime looked like a 4×4 and the clutch was telling me it was done. Time for some changes. (Photo by Jane Absalom)

It was time to put it under the knife to see how bad things really were. One of our dedicated advertisers here on TURNology is SPEC Clutches and Flywheels. I had the opportunity earlier in the year to visit its facility in Bessemer, Alabama, when I went to an event at Barber Motorsports Park in nearby Birmingham. I really learned a lot while talking to the owner David Norton.

David is an avid racer, himself. It is how SPEC was born, right there in the shadows of the Alabama Gang. David was a street racer; he was out there running imports (when imports weren’t cool, except to those who owned them) against muscle cars in the ‘80s. There was very little aftermarket support for imports in his little slice of the South, especially for drag racing applications. After numerous failed clutches, David did what any good entrepreneur would do and started making his own. SPEC made a name for itself in the import drag racing world, becoming a leader in that genre in the early days. Now, it offers high-performance clutches for just about any application from Kias to Ferraris.

There are very few builds and environments, street or track, in which the benefits of lightweight parts do not heavily outweigh downsides — if any exist. — David Norton, SPEC Clutch

Choosing the Right Clutch

It was time to figure out what clutch would work best, so naturally I called David at SPEC. I told him I was doing some HPDE, autocross, and time-trial events and asked what would be best for CrossTime.

“Because you’re not class racing like Spec Miata, you’re not limited in your choice of flywheel or clutch, so that is great,” David said. “A Miata will really benefit from one of our billet flywheels because the car is so light and low on power. Anything that will help spin the hamster up quicker will help. As far as the clutch, that is going to be based on feel. You could go with the Stage 1, 3, or 4, but the popular ‘SPEC’ Miata setup is the Stage 4 SZA364-3P for a 1.6 Miata, which is a three-puck design, with an aluminum pressure plate option. You can add the SZ61A aluminum flywheel for a 1.6. It will feel a bit like a track unit, and does not need any break-in.”

Here is the SPEC clutch and flywheel assembly we chose. This is a billet aluminum Stage 4, three-puck clutch with a billet aluminum flywheel for a 1.6-liter Miata. The lower mass for the 1.6 will help with torque output.

According to SPEC’s website, the Stage 4 unit is a solid hub version of the Stage 3. The hub is a solid eight-rivet and the assembly is heat-treated for strength and durability. It is available in a three-, four-, or six-puck configuration. The three-puck is the lightest option for competition, while the six-puck is the smoothest engagement, more for street use. The four-puck is a good compromise for both. It is street-drivable like the six-puck configuration, but not “street friendly,” due to the rigid hub. The Stage 4 is best for drag racing, road racing, pulling, rally, and drift.

Seeing this is a dedicated track car now, I decided to go with the more aggressive Stage 4, three-puck clutch setup for a 1.6 Miata, and ordered the aluminum flywheel as well. The high-clamp-load pressure plate sandwiches the solid-hub clutch with carbon-graphite friction material to the flywheel. This should result in higher-torque capacity due to the higher clamp load and higher friction coefficient material. The main reason for going with the solid hub is really just to eliminate the weight of the springs, which really aren’t needed on a race track. It also comes with a new pilot bearing installed in the flywheel already (if you order just a clutch kit, you will get one too), throwout bearing, and an installation tool to line it up. 

The “Before” Test

I wanted to do a test that would be able to show the benefits of going with this setup other than just driving impressions or a slalom setup. Both of those options have too many variables that could skew the results. So, I decided to ask Dave what the best way would be to show the difference.

“Put it on a dyno,” he said. “You probably won’t see much of a torque change, but you will definitely see the horsepower curve change. The lower mass of the flywheel with that smaller, lighter clutch will make a huge difference.”

This meant I had to do a “before” pull with the current clutch, which at the time I didn’t know was only hanging by a thread. Steve Bailey at Bailey’s Auto Repair and Exhaust in Pontotoc, Mississippi, had an opening and could get me in quickly, so I trailered the car down to his place.

Steve, along with Kevin Winstead of Big Dog Tuning, got the car setup on the DynoJet for me. I made sure my street tires were up to 34 psi each and got the water temperature up to 180 degrees. We did a Fourth-gear pull starting at 3,000 rpm that seemed to last forever compared to those high-horsepower cars you always see in videos — just over 18 seconds to 6,800 rpm. Those guys got a good laugh about it; they’re used to super high-horsepower cars with 3-second pulls! When the pull was finally complete, the SAE-corrected numbers came up and surprisingly weren’t too bad for a 188,000-mile car: 108.75 hp with 101.17 lb-ft of torque.

CrossTime made 108.75 hp with 101.17 lb-ft of torque on the stock clutch/flywheel setup. Respectable for a 188,000 mile engine. The clutch showed no signs of slipping, but we would learn later it was hurt worse than we thought.

The Teardown

The SPEC clutch came nicely boxed with all the parts shrink-wrapped together in a white box. But, now it was time to get dirty! My friend Chris Johnston came over one Saturday to help with the install. We removed the driveshaft, torque arm, and cross-brace under the front of the transmission before supporting the trans with a jack and removing all of the bellhousing bolts. We gingerly worked the transmission input shaft out of the pilot hole and let the jack down, being careful not to catch any wiring on the way down.

Once we removed the torque arm and driveshaft, we removed the bellhousing bolts and supported the transmission with a jack and worked it out of the pilot hole. It was immediately clear we had a leak as we removed the pressure plate and clutch to expose the flywheel.

Once we slid the trans out from under the car, we knew we had some problems, the bellhousing looked like it had grown hair. The entire inside was covered in clutch material fibers. There was a lot of cleaning ahead. Next, we turned our attention to loosening the pressure plate bolts to expose the clutch plate.

Definitely a sign of an unhealthy clutch. Clutch fibers everywhere mixed with oil looks like a rat’s nest!

Once we removed the pressure plate, all we could say was WOW! Half of the friction material was completely missing on the clutch plate, and of the remaining half about a quarter of it was chewed away. Amazingly, the clutch never showed signs of slipping. It would chatter at low rpm, but I never would have guessed most of the material was gone!

We definitely found where all those clutch fibers came from. Notice, there is only about a quarter of the flywheel-side material left. The clutch fibers were even packed on the backside of the flywheel. Surprisingly, the pressure plate and flywheel surfaces didn't look to bad considering 188,000 miles. There was still material on the pressure plate side, but it had damage.

I considered myself lucky it stayed together on the dyno with only one-quarter of a clutch. I guess the car just didn’t make enough torque to completely shred the clutch or make it slip at high rpm. Proof of this was the flywheel and pressure plate didn’t show much heat damage either.

Once we removed the heavy steel flywheel, we decided to weigh the entire assembly and compare it to the new SPEC assembly. The OE flywheel, clutch disc, and pressure plate assembly weighed 28.8 pounds. The SPEC assembly weighed in a a very svelte 14.8 pounds — that is exactly half of the original! After we got done with that little experiment, we got to work on cleaning everything up, which took a lot of time, effort, and brake cleaner. We called it a day and decided Sunday was install day.

After about 10 cans of brake cleaner and a hell of a lot of elbow grease, the transmission was somewhat presentable.

The Install

The install couldn’t have gone any smoother. The SPEC assembly is not only lightweight — it’s super-lightweight! I could pick up the entire assembly (flywheel/clutch/pressure plate) up with one hand. The stock flywheel alone weighs more than the entire SPEC assembly. Before Chris arrived, I was able to install the flywheel. I put some Threadlocker on the bolts and torqued them halfway. Then I took a breaker bar and put the socket on the crank-bolt to hold the engine from turning over as I torqued the flywheel bolts the rest of the way to 98 ft-lbs.

The new SPEC Clutch assembly is so pretty, it's a shame to hide it away under the car. The billet flywheel comes with a replaceable surface, so you don't have to get it resurfaced. The clutch matches up with the pressure plate perfectly (note the sticker telling you which side is the flywheel side). A new throwout bearing is essential when replacing a clutch (do it while you are there!).

SPEC provides the throwout bearing and an install tool to line up the clutch-plate between the flywheel and pressure plate — which makes the job so much easier. I plugged the flywheel hole with the tool and installed the clutch on it as well. Now, the pressure plate went on.

Another nice attention-to-detail touch SPEC does is it puts a yellow marker on the flywheel and pressure plate to make sure you have it lined up and balanced correctly. I lined up the marks and hand-tightened the bolts after applying some Threadlocker. Once everything was in place, I started the torquing procedure to pull the pressure plate down evenly, moving from one side to the other until all were at 22 ft-lbs.

Here is the assembly being installed. SPEC provides the plastic install tool which holds the clutch in place while you install the bolts. You can remove it once you've got it hand-tight. Afterwards, you will go around an torque them in a star pattern. Also, note the yellow marker to make sure you have it aligned correctly.

When Chris and my other friend Maverick arrived, we were ready to stab in the transmission and reverse the removal process. We go the trans under the car and balanced it on the jack. I worked the jack as Chris steered the throwout bearing onto the input shaft while lining up the clutch fork with the slave cylinder and getting the bolt holes straight. The last 1/4-inch took a little jiggling to get it in, but we finally got the bellhousing mated to the engine and installed the bolts to 70 ft-lbs. Finally, the torque arm and driveshaft were installed and we were ready to test.

Here you can see Maverick and Chris installing the torque arm. We noted that Chris’ beard looked a lot like the clutch material we removed the day before!

We kept the car on jackstands while I fired it up. As I slowly released the clutch, it engaged and the wheels started spinning. I went through the gears to make sure everything worked before taking the car off the jackstands for a test drive. Being this in not a street-licensed car, I drove around in the neighborhood. Everything checked out fine.

The great part about this clutch is it doesn’t need a break-in period, it’s ready to go right out of the box. Lucky for me, because I was trying to figure out where I was going to drive it 500 miles with no tags on it! And, I had two track events coming up. All that was left to do was drive it in anger.

Driving Impressions

The SPEC Stage 4 clutch is made for competition environments, so when it engages you know it. It does have a bit of an “on/off” bite to it. The three pucks grab hard, and if you don’t give it enough throttle you will kill it, or it will chatter as it screams at you for more power. That being said, the pedal-feel is still the same as stock so there isn’t a learning curve to get used to it with your left foot, you just can’t baby it into gear. When you are ready to go . . . go!

I’ve driven two events since the install and I’m actually amazed at the difference this setup made. Both events took place at the road course of Memphis International Raceway; the first was a charity autocross and the second was a full-track event with NASA Mid-South.

Ronald McDonald House Charity Autocross:  With so little horsepower, doing a burnout in a Miata with a stock clutch is not something that happens without water or dumping the clutch at 6,000 rpm. The ramp-up of the clutch was immediately noticeable as the car spun the tires off the line as soon as I matted the gas pedal. The car leaps off the corners now; the rpm ramps up so much quicker than before. Out of the 77 participants, I came in 20th and missed being the fastest Miata by two-tenths on an autocross that was setup very open and fast for higher-horsepower cars. Promising to say the least!

There have been a bunch of changes in the off-season: a new air-dam, spoiler, Torsen rearend, Pedders Suspension, and the SPEC Clutch. All of these made a noticeable difference when I came in 20th out of 77 cars. (Photos by Jane Absalom)

NASA Mid-South Summer in February Event: It was extremely cold (34 degrees), windy, and wet for this event. It was also the first event after many changes to the car since last year. I’ve changed the rearend to a Torsen limited-slip, installed Pedders suspension (look for a story on that soon), and replaced the clutch. All three of these things certainly contributed to my faster times, but I certainly felt the power difference with the new SPEC clutch assembly.

With the Torsen rearend we took from a part-out, I had to be careful with throttle input on corner-exit until the tires were hot or risk spinning out because the clutch spins-up so quickly. Once the track dried a bit and the tires warmed up, the car was a rocket off the corners.

A funny note: the car on the left is actually our former parts car which I stole the Torsen rearend out of. My friend (and fellow coworker) Ivan Korda bought it and is now racing with me!

I had a Corvette guy come up to me after one session and ask if it had a supercharger because I was sticking with him out of the corners until his horsepower took over. It was that noticeable! I can now four-wheel drift the car through the “M’s” (Turns 4, 5, 6) and had to shift as soon as I was pointed straight out of Turn 6. The results were astounding — I ran my fastest lap ever at MIR with a best of 1.22.21 on a still-damp track — three-seconds faster than my previous best — and there is still more in it!

That is really saying something when you are talking about low-horsepower “momentum”cars with 188,000 miles. I was stoked when I learned some of the “built” Spec Miatas were only a few seconds faster. But, the question was still stuck in my mind: was I still making the same horsepower and torque, or did the clutch/flywheel really make that much of a difference?

The “After” Test

Now the moment of truth was upon me — was it me or the parts? I took the Miata back down to meet Kevin and Steve at Bailey’s Auto and Exhaust to test it out on the same DynoJet with the same parts. (For the record, the Torsen and suspension were also on it for the “before” pull, so everything here was the same other than the clutch). Again, we verified the tires were at 34 psi, got the water temp up to 180 degrees, and shifted up through the gears. When we got to 3,000 rpm in Fourth gear, I nodded to Steve Bailey to start the log, then let it rip.

Without even looking at the results, I knew it got to 6,800 rpm much quicker! When I saw Steve’s reaction looking at the computer, I could tell he was surprised but didn’t know if it was good or bad. I was amazed to find the pull lasted 14.5 seconds — a full 4-seconds quicker. When the SAE-corrected power numbers popped up on the screen, we were all three blown away!

CrossTime made 117.94 horsepower and 109.04 lb-ft of torque! A huge improvement to say the least and definitely proof that lowering the rotating mass is a big deal when it comes to making horsepower in a low-horsepower, lightweight car like a Miata.

After swapping in the SPEC Stage 4 Clutch and billet flywheel, we returned to Bailey’s Auto and Exhaust to see what difference it made. And wow, what a difference. Eight horsepower and eight lb-ft or torque, for final numbers of 117 hp and 109 lb-ft of torque!

Now, although I can say all of the horsepower improvement in this particular situation can be attributed to the new clutch, the fact remains that the condition of the old clutch may have affected the original numbers — even though it didn’t show any outward signs of slipping, it was probably compromised. I can’t say that you will see the exact same results, but I bet you will see some improvement. When you’re making just north of 100 horsepower, even two horsepower can make the difference between coming in First or coming in Fifth.

I asked David to give me a final thought on why this light setup worked so well. “We’re often asked about the benefits and downsides of lightweight parts, and even sometimes why we offer so many lightweight clutch and flywheel options,” he says. “There’s no need for a sales pitch, as there never is when the benefits are infallible. We simply cite dyno results and refer them to those who make their driving impressions available. There are very few builds and environments, street or track, in which the benefits of lightweight parts do not heavily outweigh downsides — if any exist. It’s true every car is different, and based on an owner’s unique situation, we may recommend a median mass reduction at times. So, please call us for direction on lightweight components before you purchase, but for a track rat like this project, 99.9 percent of the time we will recommend the lightest setup.”

If you are in the market to replace your clutch, I highly recommend giving the experts at SPEC Clutches and Flywheels a call and talk to them about you driving style — I’m sure they have a clutch assembly that will make you as happy as I am. For more articles on Project CrossTime, you can go to the build page HERE. If you need me, I’ll be at the track hounding Corvettes! 

He may have me on the straightaways, but I’ve got him in the corners! (Photo by Jane Absalom)

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About the author

Shawn Brereton

Shawn is a lifelong car enthusiast who appreciates all things automotive. He is the proud owner of a blown '55 Chevy, a daily-driven '66 Fairlane with an '09 GT500 drivetrain, and a '96 Miata track car.
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