Good-Win Racing 2006 Dedicated Track 'NC Light'
The NC Miata is too heavy! As the owner of Good-Win Racing, I have been hearing that complaint about the third generation Miata at track and autocross events from racing customers since the third generation Miata was introduced as a 2006 model in late 2005. That lament struck a sympathetic cord with me. On the one hand, I had raced first and second generation Miatas precisely because they are so light and nimble...and my first track event in the heavier, yet softly sprung, third generation car was a bit of a disappointment by comparison. And on the other hand, I am a bigger guy and I never fit that well in the earlier Miata. Add a cage and a helmet and even with my seat bolted directly to the floor it was always a brutally tight fit for me in the early car. With introduction of the roomier third generation MX5 Miata, called "NC" by the Miata faithful, I finally feel comfy in the cockpit rather than cramped. Moreover, having also raced an RX8 for several years, I was thrilled that the new NC generation was essentially a shortened very stiff RX8 platform and that we could apply much of what we had learned from racing the RX8 suspension to the new NC. There was just real problem, though the NC has 'good bones' courtesy of the excellent RX8 chassis design that it derives from, the final result is a little chunky and lacks some of the nimble character of the earlier Miatas.
This project was born of that 'too heavy' lament, we call it: NC LIGHT. The goal is quite simple: explore the extremes of how light we can make a third generation MX5 Miata....while developing it as a no-limits track car. If "Low Weight NC" has been something of an oxymoron, our dream here is 300hp and as near 2000 pounds as we can get. The SCCA Pro Racing Playboy Mazda MX-5 Cup series has already proven that a stripped down and caged NC makes an incredible spec race car. In doing this project we wanted to go further, take the next step...not limited by the rules of a spec series we wanted to make something more extreme, and even more fun. And just to make things really interesting, we wanted the car on track in just three months...in time for Mazda's 2010 Miatas at Mazda Raceway Laguna Seca event. With a limited budget and just three months to get it running, we decided early on that we would recycle as much from the parts bin as possible into this project as long as the pieces were consistent with the goal of a uniquely super light and fast NC MX5.
Many photos, pages of information and discussion on this project on the NC Light forum thread.
With time tight, we hoped to start with a used, or incomplete, perhaps lightly wrecked MX5 Cup car. After looking at several we located a bare MX5 chassis that had never raced, had no engine, no suspension, no driveline, but did come complete with MX5 Playboy Cup cage already installed into a seam welded chassis...a perfect start for our project. Even better was that the work on this particular chassis had been done local to us by our trusted friends at AWR Racing, with whom we co-develop and market MX5 parts. Tony at AWR pulled his original file and found he still had numerous spares and other bits and pieces used in originally building this particular chassis. Soon we had the chassis and started considering our engine options.
With the goal of minimum weight paramount, we eventually decided that NC LIGHT would be a normally aspirated four cylinder. A V8 conversion with a drivetrain from a Corvette sounded like fun, but the added beefy driveline and upgraded bits didn't work with the low weight philosophy of the project. Turbo and superchargers were considered...but we already have a supercharged 2007 NC with monster size fender flares to put the torque to the ground with 18×10 wheels at all four corners. And the complexity and added weight of a forced induction extreme track machine was contrary to the vision for NC LIGHT. On the other hand, to get away from merely recreating a Playboy MX5 Cup car, it was clear that a stripped out NC with a normally aspirated 2.0 was not quite the excitement level we wanted. Our next thought was to use a Formula Atlantic 2.3. For years the Champ Car ladder series, known as 'the Atlantics', were powered exclusively by a 300 hp, normally-aspirated version of Mazda's 2.3-liter four-cylinder MZR engine, modified for racing by Cosworth Engineering. The base 2.3-liter engine has been used throughout the Mazda family in the Mazda3, Mazda5, Mazda6, MazdaSpeed6 and the MazdaSpeed3. We did eventually pick up a broken Formula Atlantic 2.3....but before that deal came together a nearly complete and functional pro-built Mazda 2.5 liter dropped in our lap.
The four cylinder 2.5 liter block is Mazda's latest family four cylinder for the Mazda3, Mazda6, etc., and using this successor motor to the 2.3 sounded like fun. One downside was that development of the 2.5 for racing is in the early stages and lacks the incredible range of hotrod parts available for the 2.3. Nonetheless, the deal on the 2.5 was too good to pass up and we liked the idea of using the future Mazda standard four cylinder. The 2.5 motor came from friends at MER Racing in Texas and had been built for a Thunderhill endurance event which the car had barely started before catching fire from the rear. The fire destroyed the car, melted the harness, yet left the engine scorched but functional. This motor is essentially a World Challenge built 2.5 from a Mazda3 with 12.5:1 compression pistons, race cams, on stock Mazda 3 block, stock Mazda 3 crank. World Challenge has a limit of 7800 rpms and the motor was built to handle that limit all day long. The head has all the usual race upgrades including stiffer springs, oversized valves, etc.. The engine was a bargain salvage, it was available immediately, and it furthered the project goals of light weight Mazda four cylinder horsepower. The challenge then became how to get that 2.5 liter motor installed properly and running in our MX5 Chassis. None of the drive-by-wire factory MX5 items such as the pedals and ECU would easily mate with this motor. The 2.5 motor included block and head, but no intake or throttle body. This is far from a plug and play operation! The 2.5 had been used by MER with a single cable operated 70mm throttle body and a Motec engine controller. We went with a used Motec of the same model figuring we could start with MER's calibration. However, on our busted 2.3 we had Cosworth's incredible Formula 1 style Barrel Throttle Body. Hmnm, we thought: 'sure would love the throttle response of the Barrel Throttle Body...wonder if these parts will mate up?'
I called up friends at Cosworth to ask about how we might adapt the used Cosworth Barrel Throttle from the 2.3 onto Mazda's latest 2.5 motor and what parts and sensors might need to be changed to accomplish the task? Our Cosworth friends voiced their support for the project... but quickly admitted that the new 2.5 block was so new in race use that they had not yet had opportunity to determine which of their hot parts for the 2.3 could be adapted to the 2.5 motor. Thus, we would be the first to find out.
Turned out, we were in luck....the Cosworth Barrel Throttle Body for the 2.3 is a direct bolt on for the 2.5 engine. We combined that salvaged 2.5 race motor with numerous hotrod pieces off the dead 2.3 Formula Atlantic motor including header, light water pump pulley, super light alternator, etc. Thermal Research built us a custom side exhaust muffler. Tony at AWR built custom motor mounts to drop the motor as low and back as possible. We added a substantial oil cooler and radiator to keep temperatures in check...and used a Motec engine computer to control everything. At our first dyno day we discovered that we had the wrong cam sensor and we pulled the sensor from the melted harness that came with the 2.5 and cleaned it up...and it still worked. Special thanks are due to Brian Sakata at Sakata Motorsports who specializes in both Motec and custom wiring harnesses. Brian Sakata adapted the wire harness for our used Motec to this engine, and tuned the Motec on the dyno. Final results: a Mazda four cylinder motor within pounds of the original but with 270 hp at the wheels....we had neatly met our goal of 300 crank hp.
I am a big fan of Ohlins coilovers, love the way they work...and their very low weight. Ohlins made us a custom valved set for this project...but while we waited on those we ended up with a free set of used Grand Am series RX8 Moton Coilovers. The Motons for the RX8 are actually slightly too long for the MX5, making install two-man job but the price was right. To keep weight as low as possible, we used a set of super light SWIFT coilover race springs with the Motons. Sways are from our RX8 catalog and we change them depending on track (we use our Racing Beat RX8 rear sway bar at some tracks, our Hotchkis rear bar at others, etc). Delrin bushings are used in all the suspension arms and links along with our heavy duty end links.
Gone! Everything inside that isn't required for speed is gone. We added back an excellent FIA approved Cobra Suzuka seat to keep us safe and comfortable for track days along with a six point harness. For data we use an AIM instrument display with lap timer that includes programmable data logging. For control there is a high grip and comfortable quick release Sparco steering wheel and adjustable Tilton pedal box. The center stack is a simple aluminum panel with dip switches for essential functions like fuel pump power, etc. A full fire control system is included. The dash topper is a single piece of carbon fiber that weighs less than a pound.
The doors are all carbon fiber...and weigh just a few pounds each. The front nose and fenders are just one piece...all carbon and incredibly light. Both items are now standard production items in our catalog so that other enthusiasts can duplicate our efforts without starting from scratch. The factory hardtop is 55 pounds but the aerodynamics of running the top outweigh the weight gains at higher speed tracks. Therefore, we started work on a 15 pound carbon fiber hardtop which finished in time for this story, and can be seen in the pictures here, though it was not complete in time for Laguna. We also have a carbon GTC-200 rear wing for downforce, matched to a front aluminum splitter fabricated on the car by AWR.
Brakes, Wheels and Tires
We used our MX5 Big Brake kit up front consisting of 13 inch rotors and Four piston calipers. That's a substantial upgrade in thermal capacity but also saved over five pounds per corner off the stock brakes thanks to two piece rotors and the aluminum calipers. We matched the front setup with two piece rear RX8 rotors and calipers. Keeping the car off the pavement are several sets of ultra light Enkei wheels including PF01 and RP-F1, depending on the event.
Time for Laguna Seca!
NC LIGHT made it to Laguna....just barely! We barely had it bolted together in time to test and tune it lightly during a local autocross event the weekend before Laguna...and set top time of day! The car then went into the paint shop. The paint was still curing as we loaded it on the trailer for Laguna. The last thing we did before getting it on the trailer was to check our progress on weight reduction by putting the car on a quad scale setup. Total weight, with FULL tank, 2126 pounds!
Thus, without the full tank we are well down under 2100 pounds and getting real closer to our 2000 pound goal. We had run out of time to finish some of our final adding lightness' projects including a switch from the standard 25 pound battery in the car's trunk to our 11 pound race battery, and perhaps a carbon fiber trunk lid. Thus, more adding lightness remains to be accomplished but the goal is in sight. Already NC LIGHT is an amazingly light NC, amazingly light for a Miata for any year....let alone a Miata with a full cage and fire control system and 300 hp. NC LIGHT was a big hit at Laguna and we used the event to complete our installation laps, test settings and check for leaks, balance, etc. Amazingly...it still feels like a Miata... as light as any first generation track Miata, yet far stiffer, with a Mazda powered heart that just screams as the rev counter passes 8000.
For updates on this project visit our Good-Win Racing Forum "NC LIGHT" thread
Showed NC LIGHT at MiataFest 2010 and it was a popular car....won the Best Modified Body Award.
Good shots of the Tilton Pedal set and other interior items. Notice the discoloration on the exhaust can, which reveals where the heat is hitting the surface (giving you an idea of the internal double chamber construction).
NARRA News from the Chuckwalla Vallye Raceway:"Brian Goodwin posted the quickest time in TT-2 on both days in his Mazda MX-5"