Justin’s RX-7: Domestic Dalliance

After league night at the local indoor karting track started to feel a little repetitive, Justin Merritt began considering his options. He’d always wanted to jump into track driving, and with the foundation laid by lots of wheel-to-wheel kart battles, he felt ready to step into full-sized sports cars. With his Scion FR-S, he moved rapidly out of autocross and into HPDE at Sonoma and Thunderhill, the two closest tracks to his home in Reno.

After making the usual list of track mods, he felt he started to see the short-term potential of the car. Truth be told, he’d gotten tired of his friends in fast Mustangs 5.0s leaving him on any straighter sections of the track, and so decided to make a shift into a sportier platform.

Weighing only 2,750 pounds wet, this V8-powered RX-7’s acceleration put him ahead of his Foxbody-driving friends.

The car had to be sensible, though. Justin hadn’t splurged for a truck and trailer yet and so he wanted to be able to make the trek over the Sierras in some comfort – at least the comfort of knowing his car wouldn’t likely leave him stranded. He’d had a thing for old RX-7s. The FC, in particular, and its doorstop shape left him feeling a little smitten.

Though he was in no position to start and finish a complete V8-swap, the thought of that had stimulated his imagination. Unfortunately, most of the typical examples of V8-swapped FCs have lived hard, unloved lives, and he knew better than to get involved with a thirty-five-year old Mazda with cut corners.

He had the good fortune of finding a half-completed ’89 that had an LS1 conversion underway. Along with the 5.7-liter in place, the previous owner had fitted a Tremec T56, a few cooling modifications, and a questionable exhaust setup.

The car’s wiring needed work, though. Whatever – the cost and the promise of a lightweight, rear-drive sports car with a fairly modern Chevrolet LS motor was worth sorting out a rat’s nest.

JTR headers, the custom y-pipe and 3” exit, a Summit CAI, and a tune from Gabe at Real Performance in Reno, Nevada, net 320 whp and 330 lb-ft of torque.

The ECM received no signals regarding coolant temperature or oil pressure, and the connector to a coil harness, well, one of its pins had backed out and caused a misfire. All fairly simple fixes. The ECM, as he found out, wasn’t even bolted down.

Once the electrical gremlins were sorted, Justin had to address some of the shoddy exhaust work. Some tubes were round, some were square, and they leaked everywhere. He left these to his fabricator friend, who added a set of JTR longtube headers, a custom y-pipe, and an HKS 3” single exit.

When all those issues were resolved, Justin had the confidence to start using it as an occasional daily. However, it was on stock suspension, so it nearly wheelied every time he stood on it.

When the time was right, he threw a set of BC DS coilovers (8k/6k) as well as the entire Parts Shop Max catalog at it. The adjustable rear toe links, adjustable toe and camber rods, new wheel bearings, a set of special bushings to do away with Mazda’s active toe, trailing arm bushings, and the typical swaybar bushings and front control arm bushings made a night and day difference.

To cap the first round of modifications off, he opted to install the larger four-piston Turbo II brakes along with Hawk HP+ pads and Stoptech rotors. The item tying these simple but effective braking mods together was the Chase Bays booster delete kit, which improved feel as well as offered the ability to change the brake balance with its proportioning valve.

“I didn’t know why there was a rattling noise coming from the passenger’s footwell until I noticed the new carpet and decided to look underneath it. There it was: the ECM, unbolted and bouncing around like a soda can.”

That helped set the nose, as did a reasonably wide track up front 255-section Kumho V730s at the end of the front axle, and 265-sections Falken RT660s at the rear.

The aluminum V8 isn’t the heaviest motor around, and though somewhat longer than the rotary it replaces, it doesn’t seriously disrupt the RX-7s famous balance and responsive front end.

That footprint proved more than adequate on the autocross, where he found he didn’t have much difficulty putting that power down. Not too shabby considering the car still runs an open differential.

Where it struggled slightly was in cooling. “I thought the big Spal fans and Griffin radiator would be fine on their own, but it overheated on hot days. I looked a little closer and saw that the radiator needed some ducting.”

With a little homebrewed ductwork and a few blockoff plates, he could redirect the air into the cooler and keep the LS happy in any temperatures. During his first outing at Thunderhill West, he was able string enough laps together to get a sense of the line, and went quickly enough to lap the clockwise configuration in 1:32.

It’s been an exciting eighteen months with the car, but it’s now looking for a new home. The reason? Justin’s looking for a new home of his own. A down payment must take precedence over a track toy, so anyone in the market for a nicely sorted, lightweight, visceral track RX-7 with the perfect amount of power ought to take a look at its listing.

Johnson's RX-7: Refreshingly Reliable

Title photo: @Yunnizhai

Misc. photo: CaliPhotography

Running through the spec lists of the boxy cars which caught his eye, he found one member of the Gran Turismo garage with an unusual engine configuration.

Two-rotor, 1300 cc.

That was when the seed was sown. A ten-year-old Johnson Mac had found a car that piqued his boyish interest in machinery. Little did he know that this quirky Mazda would influence the direction of his career, and that, twenty years later, he’d still be tinkering on a rotary-powered car with the same sort of enthusiasm he had at the onset.

Things didn’t take off like he would’ve liked, but perhaps those years of dreaming served to build a foundation he could later build upon. It was the white FC3S from Initial D that got him to scour the local classifieds for an affordable RX-7, but he was a high schooler then without the funds to get one of his own.

First Stage

It wasn’t until a few years passed that he could have one for himself. The primered exterior and stained burgundy interior of his first FC didn’t impress many, but the reliability of the naturally-aspirated 13B engine surprised its new owner. Despite the reputation these rotaries had, Johnson learned that proper maintenance could make one fairly dependable.

That foray with an atmospheric motor encouraged him to venture into turbo territory. With the help of Fris from Lucky 7 Racing, his friend Allen, and the rest of his FAFSA money, Johnson bought an ’87 Turbo II shell, fitted a turbo powertrain, upgraded the footwork, and went autocrossing.

It was only a matter of time before he graduated to track days. After his first time on a road course, he knew he’d found the hobby he’d spend the rest of his days doing. Two frightening crashes and countless nights working in his driveway didn’t deter him from pursuing his passion, but common decency did—temporarily, anyways.

After crashing his second FC, he didn’t want to burden his roomate with another project crowding the driveway, so he parked his rebuild while saving for a house of his own. Johnson had graduated and gotten an engineering job, so the money was coming in, but he was still stretched thin.

Third Stage

Three years passed before he could acquire a house, a grip on things, and, finally, another FC. Right as he was beginning to revive his car habit, his friend from Lucky 7 Racing called about a car that might interest him: a race-ready FD3S that the customer had sold back to the shop. Money was tight, but the timing could not have been better, so Johnson took a leap of faith.

The car had been built to run in NASA TT2 and built to a high standard. In fact, it was mostly complete, save for some paint and wiring issues. It even had a running engine making twice the power of his previous Turbo II’s. He sold off the salvageable bits from the crashed cars crowding his garage and made space for his third-gen.

That was the summer of 2016. Four months and three track days later, the engine blew. “I’d had some issues with breakup at the higher revs—I knew it was wiring-related, but I never found the source of the problem until it blew. “The OE reluctors were used with connectors retrieved from an OE harness, a weakened connection which may cause erratic spark timing when vibration is introduced.  We believe this may have caused detonation flattening the side seals on a rotor face of the first engine.”

Fortunately, Fris was willing to help him install a new motor, and over the winter, the two were able to give the FD another shot at life. “I rebuilt the harness from scratch that time, made sure all the connections were reliable, and upgraded to a Haltech ECU with improved engine safeguards. The tune was and is still managed by Nelson Siverio. He is a wealth of knowledge and the reason I’m interested in tuning as well.”

With the new turbo and an E85 tune, the 13B-REW makes 484 horsepower and 400 lb-ft at the wheels.

Making sure the engine ran well within a set range of parameters was the next goal. “You need to perfect ignition timing—that’s a non-negotiable, and then ensure fueling is appropriate at all times. These engines don’t work well outside of a pretty narrow operational window, so Nelson programmed several failsafes into the Haltech 1500 to keep the engine safe.

For example, if AFRs reach 11.8 at full load—11.2 is ideal—then the ECU triggers limp mode (in several stages) and drops the limiter to 3,000 rpm. I also have several different sensors installed throughout the fuel system to ensure I’m getting more-than-adequate pressure at all times. Monitoring the differential fuel pressure has been the best way to get a sense of what’s happening on the fuel delivery side of things.”

The Haltech did more than make his powerplant dependable—it made it tractable, too. Functions like boost-by-gear and boost-by-throttle position help to limit excessive torque and outline a semi-intuitive power delivery. Despite the big single turbocharger’s rapid onset, Johnson’s grown comfortable with the way the car squirms under power—it’s predictable.

“On the mechanical side of things, I installed an OS Giken 1.5-way differential and had it tuned to suit my torque curve. The lock-up is progressive, and the 295-width tires can handle the power if I’m careful rolling on the throttle. Out of hairpins, I still drive it like a turbo car from the ’80s, though.”

Even the modern Garrett GTX3582R isn’t quite as responsive as he’d like. Well, that may be due to the fact that an old-school HKS cast manifold is causing a bottleneck, but he has more pressing concerns before he can address a slightly lumpy power delivery.

The FD3S’ weakpoint, aside from the obvious engine issues, has been the flimsy five-speed—Johnson’s been through a few. His current answer to this persistent problem is not another h-pattern, but a dual-clutch sourced from an F80 M3. As the factory BMW clutch packs can withstand 600 lb-ft of torque, they should be more than stout enough for his purposes. Additionally, the advantage of seven gears and negligible shift times may help keep him in the meat of the powerband more often—thus solving his problems in slow corners.

It’s a tall order that will require the assistance of some transmission specialists who can mate modern BMW with modern-classic Mazda, but Johnson’s engineering insights and passion for this platform should carry him through the frustrating pioneering period. His commitment to the rotary sports car over the last two decades had made him into more than a mere tinkerer. He’s almost a qualified technician now, and his last forty track days all on the same motor stand as evidence to his understanding of this lovable, finicky oddball.