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Mazda RX-7: Part 9

The Evolution of a Revelation

Shiv S. Pathak
Oct 10, 2002

It's been nearly two years and over 35,000 redline-charging miles since we acquired our 1993 RX-7 Touring Package. Other than a few minor bumps and scrapes along the way, our car continues to blaze up the local race tracks, resting only to quench its freakishly healthy thirst for Chevron's finest. With almost two years of tweaking, fiddling, testing, and flogging under our well-worn seatbelts, we feel it's about time to recapitulate of all the major work (and, of course, money) that has seeped into what has easily become the raciest project car in SCC's illustrious history. The following outline covers only the quantifiable and easily reproducible basics and ignores all the miscellaneous do-dads that have yet to be tested.

Building Your Own Beast
Now 7 years old and hopelessly misunderstood, this stellar example of what a sports car should be can easily be purchased for a song. Make sure to follow the shopping guidelines offered in Part I of the project series (December, 1998). Be sure to know what you are getting into; these cars require unique care and consideration. Fortunately, once properly set up, the RX-7 rewards your efforts tenfold... and then some.
COST: $17,000 to $22,000

High Efficiency Radiator
Perhaps the single, most glaring weakness of the FD3S (the internal designation for the third-generation RX-7) is its marginal engine cooling capacity. This is especially bad considering that overheating is almost guaranteed to destroy a rotary engine. This all-aluminum, drop-in radiator upgrade should be considered a mandatory upgrade for anyone who lives in a warm climate or drives on the track. Consider it cheap insurance. Well, not too cheap. And don't forget to buy the coolant expansion tank bypass kit ($49) and 1.3 bar radiator cap ($18) to go with it!
COST: $617 (radiator only)

M2 Performance Stage III Engine Package
Like a 500 cc shot of adrenaline, these simple, bolt-on upgrades make a quick car even quicker. Consisting of a cold air intake, large intercooler, 3-inch exhaust down-pipe, 3-inch Racing Beat cat-back exhaust and remapped ECU, this series of upgrades increased output from a meager 218 rear-wheel hp to a far more enjoyable 301 wheel hp--all without taking a toll on reliability or drivability.
COST: $3,650

J&S Safeguard Knock Sensor with Dual Monitor
After overheating, detonation is the next leading cause for rotary engine death. Considering it only takes one or two pings to send the two-rotor RX-7 into 1.3333-rotor configuration, an active form of detonation sensing is a really good idea. Even with conservative performance tuning, there's always the very real possibility of filling up with a bad tank of gas and not realizing it until it is too late. Snaps, crackles and pops should be heard at the breakfast table, not while driving your rotary-powered steed.
COST: $595

Tires and Wheels
Would Carl Lewis ever run a 50-yard dash in Velcro-fastened Keds? This same principal applies to the FD3S. There are several viable high-performance tires available, each with its strong and weak points. Our favorites have been the Yokohama AVS Sports and Toyo RA-1s. However, as good as street tires (even R compound ones!) have become in recent years, they are still slippery compared to real race rubber (like the Hoosier racing slicks we are currently testing). Our elegant but costly solution? Buy two sets of rims and tires--one for the track and one for the street! One hint: Go forged and go light. We are using Volk 17-inch TE37s on the street and 18-inch Forgelines on the track--both are light and as strong as hell.
COST: $2500 to $5000 per set of wheels and tires.

M2 Performance Suspension Package
Ah, the black art of suspension tuning. After countless hours of track testing, we ended up with the same suspension that adorns M2 Performance's World Challenge race car. Not exactly a coincidence considering even more countless hours were poured into its development as well. Included in the package are GAB Super R adjustable coilovers, upper strut plates, heavy-rate Eibach race springs, an adjustable front anti-roll bar with reinforcement mounts, strut tower brace, adjustable competition trailing arms and toe links. When set up correctly, the system performs even better than the sum of its parts. On the road, however, it can be a little stiff-riding for some tastes.
COST: $2,660

High Performance Clutch and Lightened Flywheel
With an estimated 350 engine hp on tap, a beefier clutch is a necessity. Fortunately, all we needed was a higher clamping pressure plate (plus 30 percent) and another stock, organic friction disk. After spending some quality time with a "streetable" cera-metalic clutch disk, we're more convinced than ever that organic is the way to go if the car is to be driven on the street. We eventually settled on an ACT pressure plate. Somewhere in the middle of all that clutch swapping, we installed a very trick Exedy chrome-moly lightened flywheel, improving throttle response without sacrificing drivability. There are many clutch and flywheel alternatives available, each with their share of relative compromises. Take your pick.
COST: $950 and up

M2 Performance Big Brake Package
Consisting of four-piston AP Racing calipers and authentic 13-inch AP Racing Champ Car rotors, our big brakes proved we can have it all. By simply changing front brake pads, we get quiet, trouble-free operation on the street as well as ruthlessly consistent performance on the track. For the rear brakes, we kept stock rotors and calipers and use only Hawk Blue race pads. In either configuration, the brakes offer Porsche-humbling pedal feel, glorious initial bite, and excellent front-to-rear braking bias. We had earlier tried using Aluminum Metal Matrix Composite (MMC) rotors, but based on our experience, we're not yet confident they are viable for heavy use.
COST: $2,835 with all the necessary brake pads

Kirk Racing Roll Bar
Of all the things we could have skimped on, safety is not one of them.We hope the roll bar is the one upgrade we will never test. While we can't honestly say we feel any differences in chassis rigidity, we can admit to feeling a lot less stupid when we're entering Turn 9 at Willow Springs at full speed.
COST: $350

Sum Total
Is dumping over $20,000 worth of performance upgrades on a quirky, rotary-powered sports car a defining act of sheer stupidity? It certainly is if you're looking for a clever financial investment. However, if your only goal is to drive a car that can ignite the fuse on the back of your primitive, endorphin-producing cerebral lobe while out-performing nearly anything on the road or race track, your hard-earned money couldn't be better spent.

Back to Business As Usual
As I sit down in front on my computer and try to compose the rest of this project installment, I realize my job becomes increasingly difficult as this series progresses. Nearly two years ago, the job was easy enough; to improve upon a third generation RX-7's strengths, ameliorate its weaknesses, while still retaining a reasonable amount of daily utility. These days, it's nearly impossible to follow that same premise. Why?

Because, quite frankly, our creation out-performs just about anything we dare compare it to. And therein lies the problem with Project RX-7: Its limits are too high to probe on any public street, up any empty mountain road, or through any twisty back road. Sure, it can be driven fast enough to make your head explode, but that won't tell you anything about how the car behaves at its limits. And that is precisely what this car is all about.

At this discrete point right at the top of its sizable performance envelope, Project RX-7 offers something that most other ultra-high performance cars simply can't match--forgiving speed. Not only does velocity comes so easily and so rapidly, but minor driving blunders going largely unpunished. So unique is this endearing quality that any slow-witted driving hack like myself can come across looking as if he was born with the innate ability to heel-toe downshift and confidence lift at triple-digit speeds. How the hell do we make this car any better? We're working on it. But first, let's take a couple steps back and fix a problem that have been bothering us for quite some time.

Shocking Discoveries
A few readers may have noticed that we at SCC have found yet another toy to rub our pointy little heads against. It's called the Roehrig shock dyno and it tests... you guessed it, shock absorbers. While shock dyno results are relatively easy to understand (read February, 2000 "Technobabble"), applying the results to the real world takes a great deal of knowledge and experience. For that reason, we're not going to tread through any deep waters.

For now, we'll stick with basics and leave the serious suspension tuning issues for another installment. Instead, let's compare and contrast a few different shock absorber available for the FD3S. First, look at the two factory offerings. The FD3S was available with two different shock absorbers. The Touring Package came with relatively cushy shocks, while the R1 package was a buckboard-stiff kidney pounder. Looking at the Touring Package shock's dyno results (page 272), it is clear the Mazda engineers were trying to balance the scales between decent performance and pleasantly supple ride quality. Using relatively soft springs rates (280 lb/in. front and 200 lb/in. rear), the engineers felt they could get away with minimal rebound damping. The downside is the RX-7 can feel floaty at times, tending to dive, roll, and squat during evasive maneuvering.

On the other hand, compared to the stock shocks, the Bilstein shocks that came with the R1 package (page 276) offer gobs of rebound damping--especially in the front. On the road, this extra damping results in a tight, well-controlled ride. But why the disproportionate amount of front rebound damping? Perhaps this was an attempt to stiffen the front end of the car without resorting to heavier rate springs. While shock damping doesn't influence effective spring rate or overall cornering balance, it does influence the way a car responds to input--either from the driver or from the road. To the driver, the extra front rebound damping yields, among other things, improved road feel, less squat under acceleration, and improved turn-in. What front rebound doesn't yield is extra understeer or less brake dive--as one would expect from stiffer front springs.

As its name implies, the Koni single-adjustable shock absorbers (see dyno on page 274) are adjustable in rebound only. And unlike other adjustables, the Konis do not have discrete settings in the form of discernible adjustment knob detents or "clicks." Instead, the adjustment knob spins smoothly from one end to the other, making it difficult to establish reference points and plot out individual damping curves.

Perhaps the most striking characteristic of the Konis is that, unless set to full, rock-hard, low-speed stiffness, they offer significantly less low-speed compression damping than either the stock or Bilstein shocks. While such low-speed shock valving yields a smooth ride, it also results in more brake dive and less immediate turn-in characteristics. On the rebound side, things look better. On the softer settings, high-speed rebound damping is as gentle as that of the stock shocks. And on the stiffer settings, high-speed rebound damping becomes greater than the stock shocks.

What does this tell us? For starters, it suggests Konis, by virtue of their still rather conservative rebound damping, are best suited for use with stock or close-to-stock spring rates. If significantly stiffer springs are used, the Konis may not offer sufficient high speed damping to prevent unwanted spring oscillations which would result in a floaty, under-damped ride. One thing abundantly clear is that you never want to run Konis with the adjuster cranked all the way to full hard. Low-speed damping in both directions goes super-stiff when the adjustment valve is completely closed, so they should never be run more than 1/8th of a turn from full stiff.

At first glance, it's obvious the GAB Super R double-adjustable shocks (see dyno on page 274), with their generous rebound damping characteristics, were designed with stiff springs in mind. This was one reason we opted for these shocks on our slightly lowered and very stiffly sprung project car. Another advantage of the GAB shocks is their nice, evenly spaced range of adjustments which makes suspension tuning less guesswork and far more intuitive.

Also adding to the GAB's impeccably sporty flavor is its abundant low-speed damping, which results in razor-sharp turn-in, reduced pitch, dive and roll, as well as super-quick steering response. The downside? Check out that medium- to high-speed compression damping. Yikes. Not exactly the most suitable shock for rough road commuting, is it? The moral of our story: Although we have found the shock that works the best for us, there is no perfect shock absorber. Yet. Yet? That's right, as you read this, M2 Performance is working on an independently adjustable (for rebound and compression) ultra-high performance shock that should potentially come the closest to meeting our street and track needs. Offering extensive valve adjustability, the new shocks should be able to meet any reasonable set of expectations.

Rantings of a Sparkless Lunatic
We blamed the solenoids. We blamed the wires. We blamed the coils. We blamed the remapped ECU. We even thought about blaming the All-Mighty Himself. No matter what we replaced or at whom we pointed our grungy fingers, we just couldn't seem to clean up the high rpm misfire that made full throttle blasts to the 8000 rpm cut-off less than enjoyable. But finally, we ran into the source of the stumble: A damaged electrical connector in our ignition sub-harness.

With one wire barely making contact with its terminal, the front rotor's spark plugs wouldn't spark during unusually heavy load or at high engine speeds. Not only was this the source of our top-end torque roll-off, it also explains the partial-throttle "bucking" we experienced during single-to-twin turbo transition. Of course, trying to buy an ignition sub-harness from the dealership without having to purchase the complete and very costly electrical harness is like trying to extract teeth from a digestive orifice other than the mouth.

Fortunately, famed RX-7 drag racer and proprietor of SR Motorsports, Ray Lochhead, came to the rescue, finding the object of our desires in a pile of unused parts. As they say, one person's garbage is another's treasure.

But our sparky misadventures didn't end there. Several weeks and a few track testing days later, we began to notice yet another ignition quirk, this time only during secondary turbo transition. As we were preparing ourselves for yet another fantastic voyage deep into the RX-7's dense engine bay, Brian Richards of M2 Performance posed a thoughtful question, "When was the last time you changed the spark plugs?"

Good call. Once removed, our leading spark plugs showed evidence of excessive wear. Perhaps a result of our excessive track testing, eh? "A track-driven RX-7 is very hard on its spark plugs," Richards explained, "and they won't last nearly as long as many people would expect. Sometimes they'll last 15,000 miles and other times only 7,000 miles. Either way, they are the first things that should be inspected anytime misfire becomes a problem."

Since the stock plugs fail to offer the longevity we would expect from a not-easily-replacable-without-using-a-lift-or-burning-your-forearms item, we took two steps in the right (colder, that is) direction by replacing our old NGK BUR7EQP leading and trailing plugs with four nearly identical NGK BUR9EQP plugs. Why the colder plug? Well, it appears as if the stock plugs are being put through hell. The culprit? Extreme heat, of course. And the colder the plug is rated, the less heat it retains during combustion. And the less heat it stores, the less hell it goes through and the longer it lasts. But, like everything else, there is a downside to using a colder plug. Since they don't run as hot, they don't do as good a job of burning themselves clean. As a result, they are more prone to fouling during thumb-in-the-mouth, sissy-boy driving. The solution? Duh. Do you really have to ask?

Just When You Thought It Was Safe To Pick Your Favorite Intercooler
In our previous installment (November '99), we compared two high-end intercoolers, finding that the merely large "Medium" M2 intercooler actually performed better than the simply huge "Large" M2 intercooler. While the charge cooling ability between the two units were comparable, the larger intercooler suffered from a 0.6-psi greater pressure loss. And as we all know by now, pressure loss is evil.

We concluded this extra loss was most likely the result of the large intercooler having fewer (18 vs. 22) and significantly longer (17-inch vs. 11.55-inch) cross-flowing intake channels. Fewer and longer tubes, all things equal, should pose a greater airflow restriction, right? By a unanimous decision, we declared the medium intercooler the outright victor and called it a night.

Mr. Biggie is back. Fitter than ever. And ready to put some serious hurt on the reigning charge-cooling champion. Armed with a new core design and a reshaped intercooler outlet elbow, the once-humiliated heavyweight is on a mission. And that mission is clear: To cool some hot air.

Enough of the pointy-headed melodramatics. After an evening of thermocouple wielding and differential pressure gauge monitoring, it appears we have a new champion.

These results also shed some light on what we've said in the past about intercooler design. Since both intercoolers offer identical pressure loss, it would appear that the extra core length poses no significant restriction to incoming air. Instead, we can now argue that the old large IC's 0.6-psi greater pressure loss was almost completely a result of it having four fewer internal charge tubes. Another contributor to the new large IC's enhanced pressure drop performance is its slightly revised "S" tube that offers a smoother, less turbulent path for air to flow between the intercooler outlet and the GReddy intake elbow.

According to additional comparison testing, the revised "S" pipe alone was worth a 0.1-psi reduction in pressure loss! In addition to the large intercooler's much-reduced pressure drop, cooling efficiency has also been improved measurably. This fact addresses yet another notion we once entertained regarding large, stock-mounted intercoolers. That is, we had reached the point where charge cooling was being limited by the amount of airflow that passes through the intercooler duct, and not by the intercooler itself. Obviously, with these new results, we have proven ourselves wrong--once again.

Next Time
Is this really the best intercooler? Are our expectations of the perfect, no-compromise shock absorber reasonable? Have we done everything there is to do to an RX-7? We'll find out in the next installment. Also in the works are other full-fledged racing modifications that should make the heart of any race enthusiast palpitate with excitement. In addition, we'll finally be able to quantify, in terms of drag and down-force, the effects of our adjustable rear wing. By then, we'll have gone through a set of Hoosier R3S03 DOT-approved racing slicks and will be able to give you the full story behind serious race rubber and how they compare to even the best street tires. Stay tuned.

Prices
Mazda Competition Radiator.......................$617
Expansion tank bypass and radiator cap......$67
M2 Performance Stage III kit.....................$3,650
J&S Safeguard.............................................$595
ACT Clutch..................................................$420
Exedy Flywheel...........................................$500
4 Volk TE37 wheels......................................$2,100
4 Yokohama AVS Sport Tires........................$724
4 Forgeline Suzuka wheels............................$2,550
4 Hoosier R3S03 Tires...................................$800
M2 Suspension Package................................$2,660
M2 Big Brake Package.................................$2,595
Kirk Racing Roll Bar.....................................$350

Total: .....................................................$17,628

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

C2 Automotive Inc.
1009 7th Street
Oakland, CA 94607
(510) 272-9869 (Tel)
(510) 272-9882 (FAX)

ForgeLine Inc.
3578 S. Kettering Blvd.
Dayton, OH 45439
(937) 643-0050 (Tel)
www.forgeline.com

Hoosier Racing Tire Corp.
65465 U.S. 31
Lakeville, IN 46536
(219) 784-3152 (Tel)
(219) 784-2385 (FAX)
www.hoosiertire.com

Kirk Racing Products
Mark Stewart Enterprises Inc.
1433 Montgomery Hwy
Vestavia, Alabama 35216
(205) 823-6025

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

N-Tech Engineering
P.O. Box 15
Cypress Gardens, FL 33884-0015
(941) 324-6692
www.n-tech.net

Performance Friction Corporation
83 Carbon Metallic Hwy
Clover, SC 29710-0819
(800) 521-8874 (Tel)
(803) 222-2144 (FAX)
www.performancefriction.com

Superior Dyno Service
1740 Enterprise Dr. # 12
Fairfield, CA 94533
(707) 425-DYNO (Office)
(707) 425-6062 (Shop)

SR Motorsports
320 Fairview Ave.
Brentwood, CA 94513
(925) 516-7382 (Tel)
(925) 516-8901 (FAX)
www.shaneracing.com

Toyo Tires (USA)
6415 Katella Avenue
Cypress, CA 90630
(800) 678-3250 (Phone)
(714) 229-6184 (Fax)
www.toyo.com

Yokohama Tire Corp.
P.O. Box 4550
Fullerton, CA 92834
(800) 423-4544
www.yokohamatire.com

By Shiv S. Pathak
17 Articles

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