Nearly two years ago, when we first began our RX-7 series, we set forth an upgrade guideline that we have strictly adhered to ever since. We stated that we will maximize racetrack performance while not, under any circumstance, unduly compromising the RX-7's streetability or durability. What this has meant to us is that we had to keep one foot planted firmly in the real world. A world that frowns upon unmuffled exhaust systems, squealing brakes, rock-hard suspensions, Lexan(TM) windows, and stripped, bare-bones interiors. We've been good. But now, we want to have a little extra fun. So much extra fun, in fact, that we're going to temporarily ignore our self-imposed restriction. Our reason? The need for speed, of course!
Grip of the Gods
OK, the cat is out of the bag. In the last few months, we found the one modification that transformed our raceable street car into a not-so-streetable racecar. What is it? Here's a hint: They're big, fat, and stickier than a movie theater floor after a week-long Star Trek marathon. They're Hoosier R3S03s and we're bananas for them. Compared to any other brand of rubber we've tried on Project RX-7, these road racing tires demand respect. In terms of performance, they start where the Toyo RA-1s end. The designers of the R3S03s only had one goal in mind: Grip. Everything else is meaningless. Too much noise? Wear ear plugs. Too much tramlining? Keep both hands on the wheel. Ride too stiff? Stop whining and drive. This tire is all about going fast. It's about winning races. See that DOT-approval marking? Don't pay attention to it. It's not a street tire any more than a blowtorch is a cigarette lighter. The tread might as well have been painted on with an airbrush because after a few hard laps, the tires become flat-surfaced racing slicks. Serious stuff.
Obviously, Hoosiers don't really belong on the street; they belong on trailers or crammed into the back seats of race support vehicles. The track-only nature of the Hoosier's limit their appeal, but so what? There's no other upgrade that rewards so much and costs so... uh... never mind. Although our tires (245/35ZR-18 fronts and 275/35ZR-18 rears) cost an utterly reasonable $900, they offer a UTQG wear rating of only 40, meaning that they will need to be replaced every few track days. But if your first priority is speed, they are worth every penny. Trust us.
Of course, a dedicated set of racing tires demands a dedicated set of racing wheels. Wanting something very strong, lightweight, and seriously good-looking, we looked no further than Forgeline Inc. of Dayton, Ohio. Enter the Forgeline Suzukas. Weighing a tad under 20 lbs for a massive 18 x 9.5-inch rim, the gorgeous polished aluminum Sukuzas perfectly met all our requirements. Unlike many other forged wheels, the Suzukas are 100 percent forged 6061-TG aluminum, center section and all. Also unlike many other wheel manufacturers, Forgeline does not make "universal fit" wheels. Instead, each wheel is custom-made to fit a specific application. Also notable is the amount of caliper clearance. According to Forgeline, its wheels are designed to accommodate all aftermarket brake packages. Although we can't confirm that claim, we can say that our 13-inch AP Racing big brake upgrade fits fine with a lot of room to spare. To ensure that we encountered no fender clearance problems, we opted for 18 x 8.5-inch rims up front and 18 x 10-inch at the rear. Yummy.
Less Ricey. More Racey.
Take a look at the dashboard layout of any purpose-built race car. What do you see? Not too much. That's right. No fuss. No muss. Cold austerity, plain and simple. Is this because racecar drivers are grim and joyless people? Not really (although I'm sure a few are). But rather, it's because racing is challenging enough without having a vast array of gauges, meters, and dummy lights bombarding and distracting you with extraneous information. The more attention a driver can pay to the task at hand, the faster and more consistent he (or she, of course) will be. Perhaps thinking that we need as much help as we can possibly get, Brian Richards at M2 Performance reconfigured our cockpit into something that resembles that of his racecars.
The first thing to go was the handsome 2 5/8-inch triple gauge pack (coolant, exhaust gas, and oil temperature) from Auto Meter that nestled in our glove box. In its place, Richards installed a microprocessor-controlled 52 mm dual gauge from SPA. Monitoring both fuel pressure and coolant temperature, the SPA gauge offers a selectable back-lit display, a low battery warning, and individual warning lights that can be programmed to respond to any user-definable threshold. In the quest to avoid redundancy, we also removed our Auto Meter 2 1/8-inch electronic fuel pressure gauge from the driver's side A-pillar. Only needing our Auto Meter boost gauge in plain sight, we relocated it from the A-pillar to the top of the steering column, held in place by an attractive, RX-7-specific gauge holder from GReddy.
Once the gauges were all operational, Richards installed a clever little device designed to emit an audible warning alarm anytime our J&S Safeguard knock sensor unit retarded ignition timing beyond a certain number of degrees. A warning alarm would indicate a bad tank of gas, lean run, or a host of other causes that can spell instant doom for a rotary engine if gone unchecked. Again, this threshold can be adjusted. For our purposes, we set the alarm to trigger if total ignition retard exceeds 5 degrees. Large enough to keep it from buzzing away all the time due to noise-related J&S activity, but low enough to draw our attention to significant amounts of ignition retard.
The benefits of warning lights and audible buzzers should be obvious. Instead of constantly having to read and interpret needle positions and count LEDs (as with the J&S Safeguard monitor), now we just need to notice a warning light or hear the warning buzzer. Still, easier said that done. Imagine driving on the track. The windows are down. You're wearing a full-face helmet. The sun is in your eyes. You're weaving your way through a slew of slower moving cars. You can't hear any buzzer! Nor do you have the time to look across the cabin to check for any warning lights! All of a sudden, you realize that you're using your time and limited brain power for reasons other than trying to keep yourself from flying off the track. Well, that was our situation at least. What's the solution?
How does an SPA steering wheel with integrated warning lights sound?
That's right. We're talking authentic racecar technology now. On the top of the steering wheel, there are three warning lights--each corresponding to a different gauge output. In our case, the three outputs are fuel pressure, water temperature, and J&S activity. If any of these readings exceed (or fall below, as is the case of fuel pressure) our user-determined thresholds, an LED is activated. The downside? We had to give up our air bag. [Readers are urged to keep in mind that the removal of a passive restraint system may have legal, liability and safety implications. In other words: proceed at your own risk and discretion.] As if Project RX-7 wasn't raced out enough, we couldn't resist the idea of a Willans four-point harness system, also available from M2 Performance. While the stock seat belts served us well (once cinched and locked in place), the additional grip levels afforded by the Hoosiers literally had us trying to hold on by the seat of our pants. In fact, after a long weekend of track testing, it wasn't unusual for us to notice a peach-sized patch of irritated skin on the side of our left knees. The cause? Trying to brace ourselves against the door panel with our left legs during hard cornering. With a proper harness holding us firmly in place, we found ourselves spending less energy trying to fight the laws of physics. Our knees are a lot happier as well. Double bonus.
More Electronic Trickery
Every now and then, we actually come up with a good idea. In this case, the revelation was sparked by the performance of M2 Performance's nifty little Knock Alert device. Originally designed to trigger a warning buzzer when the J&S Safegaurd becomes overly active, the Knock Alert could be modified to be even more useful. How does a boost cut sound? It sounded pretty darn good to us. Implementing this function was actually quite simple. In fact, we used same output signal that triggered the buzzer to trigger a relay that would then cut power to an electronic boost controller.
What boost controller? We chose to use a GReddy Profec-B. Like all electronic boost controllers, the Profec-B employs a solenoid box which intercepts and attenuates the wastegate signal until the desired boost is achieved. Unlike other boost controllers, the Profec-B does not incorporate fuzzy logic to optimize boost response. Strangely enough, in the case of an RX-7, this missing feature is not missed at all, due to the fact that sequentially operated twin turbocharger systems tend to "confuse" fuzzy logic boost controllers, often resulting in over-boost and erratic turbo performance. For an engine that can hemorrhage itself to death with just one or two good pings, it is our belief that fuzzy logic is best avoided for this particular application.
Installation was relatively straightforward, with much of the time spent removing the intake box in order to gain access to the secondary turbocharger's wastegate control line. Once revealed, we removed the stock vacuum control line that ran between the compressor outlet and wastegate actuator. In its place, we routed the GReddy-supplied vacuum lines to and from the black plastic solenoid box, which we securely mounted in a spacious nook just beside the ABS plumbing. Tweakers should note that the stock wastegate line, which we had removed, contained a small brass restrictor pill which is commonly replaced by tuners to raise boost pressures. Per GReddy's directions, we installed the supplied replacement wastegate lines with no such boost-manipulating restrictors. The reasoning? Because now we have a programmable solenoid!
With the wastegate pneumatics in place, we passed both a manifold vacuum line and the solenoid box's wiring harness through a passenger-side firewall grommet, under the carpet, across the center console and into the back of boost controller, which we then covertly hid in the deep crevice between the transmission tunnel and driver's side seat. (We're still working on a more elegant permanent location.) Once supplied with power and ground, the system was up and running. First, we turned the boost controller off in order to determine our absolute minimum boost level. With the solenoid now non-operational, the turbo spooled to a nice, conservative--almost stock--9.5 psi of boost. Why so much boost, despite the removal of the wastegate line's restrictor pills? Our guess is that the solenoid box itself, even unpowered and inactive, is offering a significant amount of signal restriction. This would suggest that 9.5 psi is about as low as we can go without actually having to get our hands very dirty by swapping out wastegate springs. Fortunately, we felt that 9.5 psi was ideal for our knock-triggered, low-boost "fault" mode.
Now comes the tricky part: Tuning. As we know by now, the 13B-REW is not tolerant to over-boost conditions. In fact, a couple good pings is all it takes to fail an engine. Of course, by having the J&S Safeguard installed, we have minimized or risk substantially. Nonetheless, being conservative and employing a little common sense is always the preferred method of rotary tuning. On the face of the Profec-B, there are three knobs: low boost, high boost and something called "Balance." The first two knobs, as one could imagine, are used to dial in boost levels for both the high- and low-boost settings. The third, however, is a bit more insidious, as it used to adjust the response speed or "sensitivity" of the solenoid control. With the knob turned fully counterclockwise (labeled "Mild"), boost response can be maximized. Downside? Possible boost spiking. Ugh. With the knob rotated clockwise (towards "Sharp"), boost spiking can be eliminated completely. Downside? Possible boost fluctuations or "pulsing." Annoying, but not exactly harmful.
When tuning, it's important to realize that the boost controller is only really controlling the secondary turbo. This means that one must be extra cautious at turbo transition, as boost levels could instantly spike well into the danger zone. With that in mind, we started out by setting boost knobs at their lowest possible settings and adjusted balanced control toward "Sharp." Starting on the low-boost setting, we carefully adjusted the low boost level knob until we achieved 11 psi. This was accomplished with the balance knob turned fully clockwise and the low boost knob set at approximately the 12 o'clock position.
Next up was the high boost, which to our surprise, started where the low-boost setting ended. In other words, at its minimum setting, boost was already slightly higher than 11 psi. More frightening was the fact that even a tiny, minuscule, hardly noticeable adjustment resulted in an extra 2 to 3 lbs of boost! With a steady hand and watchful eye, we finally managed to get our high boost setting to deliver a steady and consistent 12.5psi of boost. Phew. And once our trick M2 Performance Knock Alert gets triggered, it trips our little relay which then cuts 12 volts power to the boost controller. When this occurs, the solenoid box goes limp, and voila--instant boost reduction! Mission accomplished. We're gushing with pride.
Coming up...
So there you have it--a streetable racecar that doesn't give up too much utility or punish the daily driver unnecessarily. It's easy to drive and fast as all hell. Chicks dig it as well. At least that's what I'm hoping. OK, we'll admit that perhaps the least forgiving aspect of the car is the harshness of its suspension. Over rough, broken pavement, it's not the ideal source of transportation. While it's heads above many other modified cars we've driven, it's still firmer than most people would prefer. Right now, there's little that we can do about it. That is, in order to ease off on the low-speed compression damping that causes this harshness, we would have to give up some rebound control which is vital to the car's at-the-limit handling performance. (Remember, we are using heavy rate springs that are nearly three time stiffer than stock!)
Next issue we'll approach this situation from a different angle. Instead of relying on adjustable off-the-shelf shock absorbers to handle damping duties, we'll see if we can dial-in something that offers independent compression and rebound adjustability. Done properly, this should not only improve ride quality, but ultimately performance as well. A little more horsepower can't hurt either. Stay tuned!
Sources
Hoosier Racing Tire Corp.
65465 U.S. 31
Lakeville, IN 46536
(219) 784-3152 (Tel)
(219) 784-2385 (Fax)
www.hoosiertire.com
ForgeLine Inc.
3578 S. Kettering Blvd.
Dayton, OH 45439
(937) 643-0050 (Tel)
www.forgeline.com
GReddy Performance Products
9 Vanderbilt
Irvine, CA 92618
(949) 588-8300 (Tel)
(949) 588-6318 (Fax)
www.greddy.com
M2 Performance
2111 Freemont Street
Concord, CA 94520
(925) 686-9047
www.mostlymazda.com
The RX-7 is very short on dashboard space for additional warning lights and instrumentation. This GReddy boost gauge mount for the RX-7 (above) and SPA seteering wheel (right) with three built-in warning lights are both great solutions. We did have to lose the airbag for the steering wheel, though.
This little add-on box gives an audible alert and cuts boost pressure when the J&S knock sensor detects too much detonation.
These Willans harnesses, with their single latch, are far easier to deal with on a street car than your typical racing harness.
As if you needed any more proof that the RX-7 is a true driver's car, notice the way the seat is designed to accept racing harnesses.
The GReddy Profec B is one of the simplest electronic boost controllers on the market. Using old-style, non-fuzzy logic, this is actually the best kind of boost controller for the RX-7's sequential twin-turbo setup. Fuzzy logic, it seems, gets confused by the unusual boost management strategies of the twin-turbo system.
Underhood space is tight, but we managed to squeeze the Profec B's boost-control solenoid in next to the ABS.