Super Street Network

Due to the EU’s Global Data Protection Regulation, our website is currently unavailable to visitors from most European countries. We apologize for this inconvenience and encourage you to visit for the latest on new cars, car reviews and news, concept cars and auto show coverage, awards and much more.MOTORTREND.COM
 |   |   |  Mazda RX-7: Part 6
Subscribe to the Free

Mazda RX-7: Part 6

Finally! Back In The Saddle Of Our Rotary Powered Thoroughbred. But Is It As Good As Before?

Shiv S. Pathak
Oct 10, 2002

Project RX-7 has finally returned to the land of the living--and it's back with a vengeance. Despite its share of misfortune, there is no denying our irrepressible Mazda is here for the long haul. But before we get too deeply involved in the current state of affairs, let's review some of the car's colorful history.

In Part I (December '98), we evaluated our pristine, bone stock '93 RX-7 while offering a "buyers guide" for potential owners. Then in Part II (January '99), we discussed the car's inherent shortcomings and initiated the early stages of our build-up starting with reliability-enhancing tweaks. Engine cooling and a big brake upgrade were the major topics we addressed in Part III (April '99). We delved even deeper into Project RX-7's performance envelope in Part IV (May '99), when we safely increased power output by nearly 90 rear-wheel hp.

We were on a roll, but as fate would have it, we ran into a nasty obstacle in Part V (July '99), when an employee at a local franchised tire shop took the car out for a high-speed test drive and crashed into a parked car. Luckily, no one was hurt. But seeing a car as beautiful as our Project RX-7 lying lifeless, sandwiched between a BMW luxo-barge and a chain-link fence, was like witnessing the scene of a gruesome crime--almost enough to make a grown man vomit. Torn plastic and shattered glass littered the accident scene like garbage on the cinema floor after a day-long movie marathon. But enough dwelling on the past. Especially considering the fact our future was starting to look surprisingly bright.

It should come as no surprise to our loyal readers that a few months have passed since our last Project RX-7 installment. During this time, Brian Richards of M2 Performance gathered up everything we needed to update our battered '93 model's body to Japan-only '99 specifications (a full report on the '99 RX-7 was in the September '99 issue). During its hiatus, Project RX-7 has also been a temporary visitor to more than a few large, well-known auto body repair shops. Unfortunately, all of them were a bit hesitant in allowing our magazine (especially one annoyingly critical owner/writer) to document and photograph the entire repair process, from start to finish. Why? Perhaps no one wants to reveal the hammering, cutting, bludgeoning, welding, crying, etc., that goes on behind closed doors. Or maybe no one wants to be responsible for a well-known and extensively modified supercar that, after being fixed, isn't so "super" anymore.

With no obliging repair shops in hand, we were forced to redirect our efforts elsewhere. Dejected, depressed and suffering from rotary withdrawal, we focused our waning attention on smaller, more personalized, auto body shops that (we hoped) wouldn't mind the challenge and risk involved in repairing a one-off magazine project car. We visited a few such shops, but none impressed us more than Kee's Auto Body of Concord, Calif.

Owned by Kee Huynh, Kee's Auto Body has been specializing in customized imports for nearly a decade. Pay a visit and you will find Huynh and his friendly employees mindfully working on any number of exquisite sport compact show cars, all of which would look right at home gracing the pages of this magazine. Fortunately for us, Huynh had no problem with repairing Project RX-7 despite our awkward omnipresence and silly photography-related requests ("Stand right there, hold this hammer, and don't move for the next ten seconds"). Clearly, he has nothing to hide. More importantly, he has patience. And after examining examples of his finished work, we are not surprised.

Project RX-7: On The Operating Table
It's rare to be witness to the internal affairs of an auto body shop. For that reason alone, we're going to shed some light on the entire process. Although it may not be exciting as chasing down Vipers at Thunderhill, the topic is newsworthy, nonetheless. The first step in repairing a wrecked car is known as the "tear down." As the name implies, this stage involves the removal of all damaged body panels and parts in an effort to get a clear picture of the full extent of the damages. In our case, once the front quarter panels and bumper cover were removed, we discovered Project RX-7 had indeed suffered what most believe to be the automotive equivalent of a death sentence: Frame damage.

Fortunately, the damage was isolated to the small section of the frame in front of the driver's side strut tower. This means the critical "mid-section" of the car was still perfectly intact. With such minor and localized frame damage, the prognosis was excellent. So how do you straighten a frame? Answer: Like a prisoner on a torture rack. The car is clamped in place by its frame rails, adorned with chains, and literally pulled straight by unrelenting hydraulic machinery. As a finishing touch, once straightened, Huynh wielded a welding torch, chisel and hammer to artfully bend, reshape and strengthen a few hard-to-reach areas of the frame and radiator support. A little bit of grinding and a few shots of black spray paint were all that was needed to completely obscure any obvious clues frame damage--absolutely amazing.

Unfortunately, the Mazdaspeed carbon composite vented hood did not fair so well. Cracked in three places, scuffed on top, and splitting down the front edge, we were uncertain it could even be repaired. However, Huynh--ever the optimist--was convinced it was perfectly salvageable. Using a series of adhesives and strengthening materials, he carefully mended the hood to good-as-new condition. The only clues of repair were a few blotches of hardened maple syrup-like goo visible only on the underside of the hood.

Project RX-7: The Mazda Makeover
Now came the time to install the brand-new '99 front bumper. The good news: All the openings on the front fascia were significantly larger than before and should, theoretically at least, allow more air-flow through the radiator and oil coolers. The bad news: The presence of a sinfully ugly front license plate holder Mazda integrated into the front bumper. "Why?" you ask. Beats us.

Our best guess is front license plate laws are far more strict in Japan than they are in the States. With this in mind, one could argue that Mazda's new bumper design, when garnished with the use-or-be-punished front license plate, allows more air flow through the radiator (and supposedly looks better) than a "normal" bumper equipped with a front plate mounted awkwardly by a generic bolt-on bracket assembly. Regardless, those who are blessed with a finer sense of aesthetics would feel it is a crime to desecrate the irreverent RX-7 with a front license plate.

This, however, would mean that recessed plate holder had to go. And, thanks to Huynh, that's exactly what happened. Keep in mind, this wasn't routine surgery. In fact, the process was quite involved and remarkably time-consuming. First, Huynh reinforced the inside of the bumper cover with a panel of Fiberglas--making the curved plastic more rigid and easier to slice and dice. Then, he cut away the entire recessed license plate holder portion, leaving a massive hole that begged for immediate attention. Initially, Huynh planned on removing the front section of the old bumper (which was still intact, for the most part) and using it as a direct transplant. However, upon closer inspection, he noticed the old donor bumper had a slightly different curvature that would not "line up" perfectly with the rest of the '99 nose. Undeterred, Huynh solved the problem by removing two portions of plastic off the side of the '93 bumper, artfully mating them with plastic weld and transplanting the assembly into the eagerly awaiting patient. After many bouts of plastic filling, repeated sanding, and artful curve-matching, the new-and-much-improved bumper cover was complete and, like the rest of the car, ready for its date with the sealed, dust-free, and temperature-controlled painting booth.

Watching a car getting prepped for painting is like watching a documentary on how ancient Egyptians mummified their deceased pharaohs. By the end of the process, layers upon layers of masking tape, paper, plastic wrap, and cloth were carefully shrouded upon our Mazda, exposing only the areas needed to be painted (front fenders, Mazdaspeed hood, and nose). With a steady hand, a discriminating eye, and one heck of a paint gun, Huynh painted the bare (but newly primed) surfaces. Concerned the color of the newly painted body parts wouldn't perfectly match the rest of the car's seven-year-old OEM paint, Huynh partially painted both doors, and in the process, carefully blended the old paint with the new. Once the painting process was complete, two layers of clearcoat were added, giving the car the much desired but rarely attained "wet look." With the car already glissening with brilliance and style, the last step involved a comprehensive finishing, polishing, and waxing.

A day later, Project RX-7 looked as good as new, fully adorned with a new front end, parking lights, taillights and a snazzy vented hood. All complete and ready for the road, we paid a visit to William Chang at C2 Automotive Inc. for an unusually accurate four-wheel alignment. Within an hour, Project RX-7 was back to its old self and original specifications.

Without A Hitch? We Think Not.
Although we were hoping all our diligent restoration efforts would be rewarded with a viceless outcome and a complete absence of teething pains, this wasn't exactly the case. The first glitch we encountered was the '99 front bumper reinforcement that had to be trimmed to fit flush underneath our modified bumper cover. Second, the stock plastic under tray/splash guard had to be re-routed slightly to fit with the new nose piece. The new twin bulb '99 parking lights also presented us with a slight inconvenience. We discovered the electrical connector didn't match up, forcing us to cut, rewire and install a set of old-style connectors. Cooling and airflow management issues also abound. First of all, the stock oil cooler ducts didn't come close to mating with the new bumper's much larger cooling intakes. Mental note #1: Order '99-spec. oil cooler ducts. Also, the space behind the radiator support and the inside of the new bumper is not sealed off--allowing incoming air to flow over, not just through, the radiator and intercooler duct. Mental note #2: Get creative with plastic paneling, a razor blade, and tie wraps. Lastly, we found that Mazdaspeed's incredibly lightweight carbon composite vented hood doesn't like to stay in one place when slicing through the air at speeds greater than 60 mph. Because we first noticed this problem when we ran with the stock bumper, our current airflow situation should not be held responsible. While it's highly unlikely the hood will catastrophically detach and tumble over the car's roof, seeing 1 to 2 inches of turbulence-induced hood flex is still disconcerting. Mental note #3: Install hood pins before the next visit to the track. While these minor problems are hardly deal-breakers, they were unforeseen glitches that should be expected by anyone interested in making similiar upgrades themselves.

Finally.... Boost Problems!
While not related to the makeover, but still a problem nonetheless, we've been noticing a turbo transition problem that first made itself apparent nearly two months before the accident. At first, the problem started off as a mild "hiccup" that happened every so often--only under partial throttle--just as the secondary turbocharger was coming on-line. As time progressed, so did the symptoms--eventually getting to the point where the secondary turbocharger wouldn't kick in at anything less than under wide open throttle. This "all or nothing" power delivery absolutely shattered the car's once-excellent daily driveability while contributing to some hairy on-track situations that all of us would like to forget. Fortunately, with the help of Mostly Mazda and M2 Performance, the problem, which turned out to be a lazy turbo control solenoid valve, was eventually diagnosed and immediately replaced. With nearly 65,000 miles currently on the clock, it wasn't surprising that our third-generation RX-7 developed sequential turbo system problems. With such a shamelessly complicated system, possible causes could be as simple as a malfunctioning one-way check valve (which is used to pressurize or depressurize the vacuum tanks, both of which are used to actuate the turbo switchover) or as beguiling as failing electrical connectors or loose vacuum lines (remember the "rat's nest" under the intake manifold). Fortunately, earlier in our project, we secured all the vacuum lines with tie wraps--eliminating at least one possible cause for these turbo problems.

Another problem we discovered was a torn lower intake pipe. According to Richards, it is not uncommon for these stock rubber "accordian-like" pipes to weaken, collapse or rupture as these cars get older. To fix the problem altogether, Richards installed a set of polished aluminum intake pipes (one for each turbo inlet).

Things Are Heating Up
During our last dyno testing several months ago, Project RX-7 spun the Dynojet rollers with an SAE-corrected 282 hp. With only 3,000 lbs (including the driver) to motivate, Project RX-7 is one fast car. Fast enough for most and perhaps too fast for a few.

But with summer now upon us, Northern California is plagued with ambient temperatures approaching, and often exceeding, triple digits. Unfortunately, hotter air means thinner air, which translates to substantially less horsepower. Compared to those cold crisp winter nights of yestermonth, where the intake charge were as dense as the hair on Austin Powers' chest, the summer brought upon turbo outlet temps approaching 270 F. Mixed with an abundance of fuel (as dictated by our remapped fuel curves), the engine is subjected to a power-robbing overly-rich air/fuel mixture.

There is a reason, however, for the rich-running condition. According to Richards, the surplus of fuel is the only thing keeping the car running safely under these extreme conditions. Without the extra fuel's chemical cooling properties, the blistering intake temperatures could lead to detonation which would instantly fracture the diminutive rotary engine's apex seals.

The root of this evil, of course, isn't Mother Nature. The real problem lies in the stock intercooler's inability to bring the sizzling hot turbo outlet temperatures (approximately 240 F) down to near ambient levels. Yet another problem associated with the OEM intercooler, especially at our higher-than-stock power levels, is an unreasonably-high peak pressure loss of 2.6 psi (which we measured during a full-throttle 12-psi run at 7000 rpm.) Such a big pressure drop across the intercooler (which we measured before and after the two rubber "elbows" going into, and coming out of, the intercooler) means the turbo is working overtime to maintain the desired manifold pressure of 12psi. Unfortunately, over-driving a turbo forces it to operate at a reduced efficiency. The end result is higher turbo outlet temperatures and a reduction in horsepower.

Cool It
Fortunately, Mazda Competition, the performace division of Mazda of America, offers an attractive "drop-in" intercooler replacement. Unlike the stock unit which has plastic end tanks and a 2.5x11.5x4.5-inch core dimensions, the Mazda Competition intercooler is all aluminum at a slightly thicker 3.0x11.5x4.5-inch. When tested, however, the upgraded intercooler only offered a marginal improvement with respect to intake temperatures and pressure losses. Surprised by our findings, we closely compared the core design of both units. We discovered the Mazda Competition intercooler, unlike the stock unit, is equipped with turbulators in the air-charge channels. While these turbulators are designed to make sure laminar air flow doesn't become a problem (turbulent flow promotes better heat exhange), they can also increase pressure drop across the core. This increase could offset the improvement afforded by its larger intercooler volume.

However, the extra core thickness brings about its share of complications as well. According to Maxium Boost by Corky Bell, the second half of the core only does one-fourth of the heat exchanging work, making it less effective. A thicker core also makes it more difficult from ambient air to pass through--reducing its efficiency even further. With these issues in mind, it is no surprise that the juggling act of intercooler design isn't as simple as it would appear on the surface. One distinct advantage the Mazda Competition intercooler has over the OEM unit is its sheer strength of construction. With no plastic end tanks to rupture or come undone (these problems are not uncommon for road racers), the all-aluminum intercooler should physically survive under the most grueling conditions. It is no surpise that these units, for this reason alone, are popular among SCCA Showroom Stock racers. But for our high-horsepower needs, this small intercooler isn't what we were looking for.

Cool It More
The next step in the charge cooling process comes in the form of two thoroughly impressive intercoolers systems, both available only through M2 Performance. The smaller of the two (measuring a whopping 3.5x12.55x11.55-inch) is the currently largest intercooler that can fit in the stock location. The larger unit, which is nearly 6 inches wider, requires a relocation of the battery. Due to their decidedly non-stock dimensions, both intercoolers require a dedicated air duct, associated intercooler piping and intake elbow--all of which are included in the system.

While we didn't get a chance to install and test the larger of the two intercoolers yet (wait until the next installment), the smaller unit yielded simply outstanding real-world results. First of all, measured pressure loss was only 1.1 psi. As a result, manifold pressures increased from approximately 12 psi to a rock-solid 13 psi. But the biggest surprise was how effective the intercooler was at bringing peak intake temperature down to within 22 degrees of ambient!

With the cooler air charge, the engine has become more resistant to knock. The denser charge also ameliorated the excessively rich air/fuel mixture. When strapped upon the Dynojet chassis dyno, the combination of the cooler charge and slightly higher boost levels yielded an increase of nearly 20 rear wheel hp! Very impressive for a passive upgrade that becomes even more effective on the road (with real airflow). Even during the fourth gear Dynojet pull (on a 100-degree morning), peak intake temperatures rose by only 49 F. On that same day, when the test was duplicated on the road, intake temps rose by only 30 F over ambient. Also impressive is the fact intake temps are within a few degrees of ambient temperatures during cruise conditions. The combination of a true cold air box and an incredibly efficient intercooler certainly pays off.

Of course, also impressive was the RX-7's real world performance. Up to approximately 5000 rpm (when operating on the first turbo), the world doesn't seem to blur by that much quicker. Above that, however, interesting things start to happen. The "switchover" is accompanied by a gratifying wad of torque (an increase of nearly 70 hp within 300 rpm), followed by a progressive swelling of turbine-like forward thrust. Above 6500 rpm, however, we experienced some distinctive misfire, which caused a dramatic roll-off in power. Nevertheless, there is no doubt that there is more horsepower to be found (heck, we're still 2000 rpm shy of redline!). But, of course, that quest is for another day. Currently, with 301 rear wheel hp on tap by only 6000 rpm, our new-and-improved RX-7 offers awe-inspiring performance while providing grin-inducing thrills. We are also looking forward to seeing how that performance translates to the track.

Coming Up...
In the next installment, we will conduct track testing at Thunderhill Park, during which time we will continue our intercooler testing by measuring intake temperatures during more extreme, sustained boost conditions. We will also quantify the effects of our yet-to-be-tested Mazdaspeed vented hood. Also in the future, we will pursue our quest for the ultimate track and street suspension set-up. Yet another monstrous big brake upgrade is on the horizon as well. The brake setup we used never ended up in production, so we want to switch from our custom setup to something that can be duplicated more easily. Of course, more tire-shredding horsepower cannot be too far away either. Stay tuned. Lots more to come.

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

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

Kee's Auto Body
2171 Monument Boulevard
Concord, CA 94520
(925) 671-9432

M2 Performance
2111 Freemont Street
Concord, CA 94520
(925) 686-9047

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

By Shiv S. Pathak
17 Articles



It was a long week, but the BRZ is done and now headed for a life of commuting and the occasional circuit flogging
Bob HernandezDec 7, 2019
Our friends from Vortech Superchargers drop by early to install one of their kits on the BRZ
Bob HernandezDec 6, 2019
After a couple days of chassis, brake, and cosmetic improvements, we've reached an important juncture in the story arc—getting ready for a boost in power
Bob HernandezDec 5, 2019
New wheels and taillights, some carbon fiber bits, and a headlight restoration job for the BRZ
Bob HernandezDec 4, 2019
Suspension and brakes were slated for Day 1. We're looking to maximize handling and agility on the BRZ and as a side-benefit achieve an improved stance.
Bob HernandezDec 3, 2019
Sponsored Links