Mazda RX-7: Part 5

Now that we are deep into Project RX-7, it's only fair to offer a brief summary of what we have done so far. The first installment of our series (December, '98) offered an RX-7 buyer's guide and established the particular goals of our comprehensive build-up. In part II (January, '99), we addressed some vitally important preparation and maintenance items peculiar to the third generation RX-7, and uncovered the car's penchant for overheating on the track. In part III (April, '99), we initiated our build-up by installing a higher efficiency radiator, strengthened sway bar mounts, and a very trick metal matrix composite big brake system from Cooltech LLC. With heat management issues in check, Part IV (May, '99) took advantage of M2 Performance's well thought-out series of power-enhancing upgrades, which yielded a very safe and conservative 65 hp increase. With a grand total of 284 rear-wheel hp on tap, we tackled suspension upgrades by installing a fully adjustable coilover system from RSlR.

Initially, this latest installment (Part V) was aimed at continuing to satisfy the power monger in all of us. We planned on installing, evaluating, and dyno testing M2 Performance's downpipe, intercooler upgrade and fuel pump upgrade. Unfortunately, a reckless grease monkey witha suspended driver's license decided to take Project RX-7 for a spin when we dropped the car off for a routine brake fluid flush. That spin ended with the driver's side front corner of the RX-7 planted firmly in the rear of a 7-series BMW. Oh, the horror!

Though the car's condition originally looked bleak, closer inspection revealed the damage was mainly skin deep. It appeared the driver's side front corner took the brunt of the impact, crumpling slightly. With no structural frame or suspension damage, the future of the car is certainly bright. So bright that M2 Performance has arranged to take advantage of this unfortunate situation by supplying the project with brand-new 1999 body parts from Japan. These updates included a revamped front bumper cover with improved cooling and intake ducts, a revised front air splitter, and a very functional, adjustable rear spoiler. By the time you read this story, Project RX-7 should be back on the track right where we left off. Our little disaster threw a big monkey wrench in the works, forcing us to redirect the focus of this installment elsewhere.

Where Exactly Is Elsewhere?
They say "God is in the little things." What "they" mean beats us, we just want our car back. Nonetheless, our plan is to use this brief hiatus as an opportunity to catch up on a few little, but important, things we missed along the way, as well as to provide a little sneak preview of what the future holds.

As a few discerning readers have noticed, what you see in the pictures isn't always what you get in the project text. In Part III (brake upgrade), you may have noticed that the RS*R coilover system was already installed, but not reviewed until Part IV. You may also have noticed a Mazda Competition intercooler upgrade was peeking out of the hood in one picture, but up to this point, has yet to be reviewed. "Why?" you ask. In an effort to carefully and fairly evaluate certain products, we often install them and don't tell anyone (including the readers) until we have a good grasp of their strengths and weaknesses. On such item that comes to mind is our clutch upgrade. "What clutch upgrade?" you ask. Good question. Read on...

Clutchtober Fest
Clutch design is a hard science based on the fact that life is full of trade-offs and compromises. There is no "best clutch." A clutch that works well for one situation may be completely unacceptable for another. A drag-racing slipper clutch, for example, would be miserable for road racing. Accepting this unavoidable truth, we decided to test two very dissimilar clutches, each designed for very different applications.

The stock clutch, built by Daikin Clutch Corp. for Mazda, mates a pressure plate with a traditional organic disk. Typically, organic friction surfaces offer very nice, driver-friendly, chatter-free clutch engagement. The trade off, unfortunately, is they are susceptible to being overheated through excessive torque-induced slippage. As horsepower increases, so does torque. While the stock clutch has been known to handle our current power levels adequately, there is no harm in looking at alternatives before they become absolutely necessary.

One such alternative is offered by Exedy Clutch Corp., the performance division of Daikin Clutch Corp. Exedy offers a unique three-puck cerametallic clutch which is designed from the ground-up to be streetable. The clutch itself is very similar to the unit used in SCC's Project Eclipse (November, '98).

The idea of a three-puck design, compared to a traditional full disc, is to concentrate the clamping force into a much smaller surface area, increasing the pressure on the friction surface. As a result, the overall torque holding capacity improves drastically. The cerametallic material can also withstand intense heat far better than stock organic-based clutches. Along with the clutch, we also installed a beautifully crafted Exedy chrome-moly lightweight flywheel. Nine-lbs lighter than stock, the Exedy flywheel was used in conjunction with a Mazda OEM counterweight. The stock RX-7 flywheel has a counterweight cast into it, so most aftermarket flywheels require the use of the separate couterweight used on RX-7s with automatic transmissions. Although the chrome-moly flywheel weighs more than its aluminum counterparts, the Exedy flywheel has been cut with large holes towards the outer edge of its surface in a serious attempt to minimize rotational inertia while maintaining a desired amount of heat-absorbing mass. The end result is a flywheel which works like a normal aluminum flywheel, but is able to withstand more heat.

Results? The Exedy clutch grabbed hard and held up wonderfully on the track. It never showed any signs of slipping or weakening, even when used extremely hard. Pedal effort was on the heavy side, but certainly not unbearable. This could be the ideal clutch for the drag strip or road racing. However, street driving was far from enjoyable. On a car that spends more time on the track than on the road, this clutch makes sense. It is streetable, as Exedy claims, in the sense that you could very easily drive your car to and from the track. If you define streetable as tolerable in traffic and normal, day-to-day, life-in-the-big-city traffic situations, we'd have to disagree.

The cerametallic clutch was not appreciated by the vast majority of drivers. After three months of usage, Project RX-7 definitely sacrificed a good deal of its daily utility and driveability. It was stalled more times than a naughty horse. Under light use, the driving experience was acceptable, but once the clutch became hot (through prolonged stop-and-go traffic), things took a dramatic turn for the worse. Clutch engagement became alarmingly grabby and borderline offensive. I soon did everything in my power to avoid driving in heavy traffic. I also quickly dismissed the notion about allowing anyone else to drive the car on public roads without a serious crash course in clutch management. Of course, there are far less driveable metallic clutches on the market. Most of them simply don't work for street application despite one's best efforts. At the end of the day, the Exedy clutch didn't fit with the goals of the project, and it was removed in favor of something more biased toward street use.

In its place, M2 Performance installed a high-performance clutch from Mazda Competition. Using a stock, organic disc and a 35 percent stiffer pressure plate, the Mazda Competition clutch offered excellent driveabilty coupled with improved torque holding capacity over the stock clutch. Pedal effort, although marginally increased, was far from being objectionable. Otherwise, it felt very similar to the stock unit. Would the Mazda Competition clutch hold up as well as the Exedy unit under repeated drag strip launches and general abuse? Not a chance. However, this is a trade- off we are readily willing to accept given the way we use the car. Once again, we have found there is no such thing as a free lunch.

So what about the Exedy flywheel? Did it work well? Indeed it did. In fact, it worked exceptionally well. Throttle response was transformed from blurred to spastic. Although it took some time adjusting to the engine's new-found liveliness during heel/toe downshifting, there was no obvious driveability trade-off. Clutch engagement (with the Mazda Competition clutch) was completely agreeable with the Exedy flywheel in place. Starting from a dead stop took no unusual effort. Perhaps most impressive was the fact the flywheel looked fresh, even after three months of abuse with the Exedy cerametallic clutch, a sign of the heat-resistant nature of the chrome-moly construction.

Pedal Upgrades: Wider Is Better
Quite frankly, when it comes to driving sports cars, being tall isn't all it's cracked up to be. Sports cars, especially those from Japan, tend to be far more hospitable to shorter drivers. Taller folks often find most sport compacts have steering wheels which sit between their knobby knees. Not only does this look foolish, it also makes heel-and-toe footwork well neigh impossible.

Why so? To execute a proper heel-and-toe downshift, the right foot must be rotated counter-clockwise so that the toes press firmly against the brake pedal while the right edge of the foot simultaneously "blips" the throttle. For those over the national average height, the steering wheel in the RX-7 can act as a very effective blocking mechanism, prohibiting this necessary leg rotation.

David Breslau, a Project Technician at the MIT Center for Space Research (no, seriously), has a solution to this height-induced dilemma. It's called the "Widefoot." Breslau, a fellow RX-7 owner and enthusiast, has developed an attractive, bolt-on pedal adapter that effectively shortens the gap between the brake and throttle pedals. This, in turn, reduces the amount of foot rotation necessary to whip off a quick heel-and-toe downshift. It works. "Wow, that adapter is actually functional," remarked Dave Coleman, SCC's esteemed engineering editor and staff giant. It looks darned nice, too. The Widefoot pedal is available in two sizes for the RX-7 and can be ordered through Crooked Willow Composites, LLC.

A Tire's Best Friend
Falling under the useful-stuff-we-would-never-think-of-ourselves category, we installed the remarkably helpful SmarTire system. Consisting of four small, lightweight sensors and one visor-mounted, back-lit system monitor, the SmarTire system constantly measures individual tire pressure and air temperatures, radioing low pressure and high temperature alerts. Installation is straightforward. One transmitting sensor (along with its counterweight) is fastened to each wheel with a large hose clamp. When the wheel is in motion, each self-powered sensor transmits air pressure and air temperature data to the system monitor every 30 and 60 seconds, respectively. With a battery life of nearly 60,000 miles, and accuracy of +/- 1 PSI, the system provides years of maintenance-free service.

But is it helpful? How could it not be? Since its installation several months ago, I no longer manually check my tire pressures before a long trip or a track event. If pressures are abnormal, we know that the SmarTire system will provide its audible warning. More importantly, who needs run-flat technology if you can effectively predict a slow leak before it leaves you stranded? It will also more than pay for itself with the cost of a single towing charge. Initially developed in England and offered as an option on the 1996 to '99 Lincoln Continental, SmarTire technology is now available in the aftermarket for virtually any vehicle that uses any standard radial tire. Of course, sensor installation is best done when you get new tires, as the procedure involves removing the tire from the rim.

Toyz 'n the Hood
What good is an RX-7 project if we fail to take advantage of Mazdaspeed, Mazda's very own performance specialty house. Offering a host of unique, OEM-quality go-fast parts, Mazdaspeed is a serious force in the RX-7 aftermarket. To test our theory that nobody does it better than the factory, we contacted Ben Miller of CSi, a Southern Californian importer of Mazdaspeed's performance products. We requested the attractive Fiberglas "Aero bonnet" (fancy name for a vented hood), a strengthened power plant frame (the bridge truss-like assembly that rigidly connects the transmission to the differential), and a short-throw shifter.

With the car in its current state of unrest, we cannot offer a full review and pictorial of the vented hood. All we can say is the hood does an excellent job in attracting stares and, most importantly, dramatically reducing the RX-7's characteristically hellish under-hood temperatures. In fact, covering up the vents with racer's tape revealed a massive negative pressure zone used to effectively scavenge much of the hot air from under the hood. Although this is pure conjecture at this moment, not only does a vented hood make the car more resistant to overheating, it could also improve intercooler efficiency at speed. We eventually hope to take before-and-after temperature measurements to verify our hunches.

Originally used in the development of RX-7's little brother, the Miata, the power plant frame (PPF, for short) is made of high-tensile steel covered with a thick laminate of vibration-dampening plastic. The PPF effectively isolates the engine's torque loads that can often have an adverse affect on the chassis. Resisting windup better than a traditionally mounted differential, the PPF design allows smoother starts and launches while contributing to overall chassis rigidity and crashworthiness. While it sounds great in theory, it would be even better in practice.

However, as Brian Richards of M2 Performance points out, the stock PPF tends to crack during extreme situations such as violent, axle-hoppin' drag strip launches. The strengthened PPF sounded like a good bet.

However, upon inspection, the unit, despite a pretty red powdercoat, looked strangely similar to the stock unit it was replacing. It was made of the same gauge steel and welded together at the same exact points. What's going on? Wasting no time and unable to speak Japanese, we referred to Mazdaspeed's product manual.

According to the literature, the strengthened PPF is constructed from a stronger steel material. With no advanced degree in metallurgy to prove otherwise, we must take their word for it and review the product based solely on its on-the-road merits. Did it make a noticeable difference with the new PPF installed? Hard to say for sure. Although I notice some changes in ride quality, the differences are very subtle. The car does indeed feel somewhat tighter over rough roads. With some more evaluation time, perhaps we can get a better idea of its merits.

One product met with unanimous and unabashed praise--Mazdaspeed's short-throw shifter. Compared to similar domestic short-throw units, the Mazdaspeed unit, as expected, looked and felt top-notch. Although the instructions were in Japanese, installation took no more than 20 minutes.

Simply remove the center plastic console, unbolt the stock shifter assembly, and replace the old with the new. Once installed, the shifter, now operating with a new fulcrum point, can be rowed through the gates with small twists of the wrist, instead of longer rows of the arm. More importantly, it doesn't exhibit the notorious notchiness and balkiness that plagues most short shifter kits. Once again, leave it to the factory to get the job done right.

Conclusions
In the next installment, we will cover the installation of the 1999 Japan-spec. updates. In the near future, we will also install, review and dyno another round of M2 Performance's power-enhancing upgrades as well as a few of their brand-new, track-derived products. Of course, we will also be returning to Thunderhill Raceway to engage in some serious high speed evaluation in our never-ending quest to discover the ultimate real-world suspension set up. Stay tuned....

Sources
Cooltech
15216 Mansel Ave.
Lawndale, CA 90260
(310) 484-2321

Crooked Willow
Composites, LLC
4655 Lehrer Drive
San Diego, CA 92117
(619) 273-7735

CSi (Mazdaspeed)
1100 S. Raymond Avenue, Ste H
Fullerton, CA 92831
(714) 879-7955

Exedy Racing Clutch (Daiken Clutch, Inc.)
8601 Haggerty Rd S
Belleville, MI 48111
(734) 454-0600

M2 Performance
2111 Freemont Street
Concord, CA 94520
(925) 686-9047
www.mostlymazda.com

SmarTire
155 Wilbur Dr NE
N. Campton, OH 44720
(888) 982-3001
www.smartire.com

Thunderhill Park
5250 Hwy 162
Willows, CA 95988