Heart of the Matter: Installing an Engine in a Spec MX-5

The third-generation Miata, the NC, has an unfortunate reputation. Seen as the only chubby member of an athletic family, it bears a heavy load. It’s often passed by when lighter, cheaper earlier generations are still so plentiful.

However, the softer-edged sibling has a few strong points to help counter its doughy image. It has room for larger brakes, wider tires, and a bigger driver, a more sophisticated rear suspension, and a larger motor.

Like the BP engine that powers the NA and NB Miatas, the NC’s MZR engine is a tried-and-true powerplant, with a host of applications that have proven its reliability. The fact that it has been adopted by several race schools, Indy Lights, Indy Pro 2000, and USF2000 to power their cars is evidence of real durability. It’s also the power plant in the NP01 EVO.

Of course, longevity is important, but with the NC’s 2,500-pound race weight, it must produce more power than its predecessor. In the case of a Spec MX-5 Challenge car, the 2.0-liter MZR produces plenty of power, thanks to a few easily controlled modifications. These additions, plus a straightforward design, were devised to prevent this series from devolving into a spending competition.

Mazda’s R&D work done in advance make the MZR easy to assemble in any garage.

With a Roush cylinder head, Kooks headers, Mahle pistons, and a C&R cooling system, the MZR makes right around 170 horsepower and 150 pound-feet of torque at the rear wheels. For a car only weighing a couple of hundred pounds more than the typical Spec Miata, that’s quite a lot, especially when it’s sent through a reinforced six-speed gearbox.

The right ratios and snappy shifts help the Spec MX-5 lap power-hungry tracks like Road Atlanta some 4 seconds faster than a front-running Spec Miata. Best of all, just about every car on the grid should be performing at this level throughout most race weekends.

The Pursuit of Level Playing Field

Mazda took three approaches to achieving mechanical parity with this engine. The first is that the flow and combustion characteristics are optimized. Second, the already tight OEM tolerances are further tightened during the optimization process, with the result that sample-to-sample variation is low. Finally, a set of measurement tools are available to make it easy for sanctioning bodies to check if an engine has been modified.

The ECU also makes life easier for the tech inspectors. The “computer is phenomenal,” proclaimed Sean Hedrick, owner of MiataCage and consultant on this Mazda project. “The ECU gives information on numerous functions that a basic OBDII-style computer just can’t.” This, combined with severe penalties for engine tampering, disincentivize cheating and keep the focus on driving. “Essentially, we designed this package so that we wouldn’t have to play games as the class size grew,” added Hedrick.

This mindset was present when developing the other parts that make this iteration of the MZR a well-rounded, well-planned, potent powerplant. For 2020, the Spec MX-5 variant received a few upgrades in the form of domed pistons, a CNC cylinder head, and the aforementioned ECU.

Pistons and Parity

The Mahle pistons are dependable. The forged pistons are more exact due to machining processes, a machined piston crown, and the high standards of Mahle’s allowed tolerance. It’s not only the racers who appreciate the pistons’ construction, but the sanctioning body as well.

The phosphate coating of the Mahle piston has a unique gray color, tampering with which is clear.

Mahle’s experience in highly regulated categories of motorsport plays a part in all its designs, and that makes tampering with this particular piston obvious. The phosphate coating of the piston has a unique gray color, tampering with which is clear. This coating also doubles as a dry lubricant film to provide a protective barrier in the pin bores and ring grooves until the oil system of the engine reaches operating pressure.

CNC Cylinder Head

Going with Roush for the cylinder head was done for a few reasons. Because parity is paramount in the Spec MX-5 Challenge Series, Roush’s experience meant Mazda could expect consistency in the product.

Roush can replicate identical cylinder heads over and over to the tightest of tolerances, thereby eliminating the need for a complicated rule set to level the playing field. This also eliminated the need to select the best possible core cylinder head to be competitive within a rules set.

Cooling and Space Constraints

Such an emphasis on parity made drafting a fundamental part of racing this car. That makes for close racing, but a standard radiator simply cannot operate well when a car ahead is blocking cool air from passing through its fins.

C&R, a longstanding supporter and contributor to efforts in NASCAR, IndyCar, and IMSA, knew the Miata platform well enough for Mazda to seek its assistance. It wasn’t only the company’s experience with hot, high-horsepower motors that drew Mazda. C&R’s success in building a popular radiator for the NB-generation Spec Miata helped the company design a product for the Spec MX-5 in a reasonably short span of time. Even though the upgraded radiator occupies the same area as the standard item, its extruded core and fin design improve cooling tenfold.

C&R developed the radiator and oil cooler heat exchanger in one package.

Many oil cooler adaptors on the market ignore the priority oil flow of the engine, which routes the oil through the filter first, leaving as much as half the oil to flow directly into the cooler and through the engine without touching the filter. Mazda Motorsports’ solution, however, sends all of the engine oil through the filter and then to the oil cooler, a more effective path for the oil. It’s a comprehensively considered engine, which is designed to perform in all senses of the word.

The Spec MX-5 engine sends all of the oil through the filter and then to the oil cooler, improving filtration and cooling.

Another Breezy Installation

By the time the sealed motor arrived from Mazda, the Couches had already prepared the bay as well as they possibly could. The stripping, cleaning, sanding, and powdercoating took the most time by far, and because the two had carefully planned a color for fittings as well as a new coat of paint for the engine bay, it’s fair to say that this detailed preparation phase, if you could call it preparation, was where 90 percent of the engine-related effort was spent. With the attention paid to detail here, “prep” seems like a huge understatement.

Powdercoating various pieces in metallic red added to the prep time.

“Well, I can’t exactly call it a show car, but the engine bay is very pretty,” Dave remarked. In addition to powdercoating many of the fittings in their signature metallic wine red, they decided to paint the bay. With a second coat of white laid down beforehand, Wyatt and Dave would have an easier time identifying leaks in their exhaustive post-race inspections.

The spec Kooks header has thick and tidy exterior welds and a Mazda Motorsports badge.

Of course, prep work wasn’t just dedicated to cosmetics. Dave went through the wiring harness, which had its fair share of corrosion. He then sent the injectors out to Haag Performance to be flowed, then dropped off his gearbox at Buttonwillow where RM Motorsport hauled the transmission back to Los Angeles and installed the Mazda bronze bushing kit to fortify it for racing.

“Dropping the motor in place probably took 15 minutes,” Dave laughed.

The radiator shares the same dimensions with the factory item, so that went in easily, as did the oil cooler, which bolts on as a replacement for the factory oil filter plate. Dave made good use of the provision for extra sensors on the adapter as well.

Dropping the Mazda Motorsports turn-key engine and transmission into place took less than half an hour.

With this motor, Wyatt and Dave will run as many diagnostic systems as they can. Mounting and wiring the extra sensors for their optional AIM system required some extra effort, especially since, as is normal with this build, and they did it without cutting a single corner.

For further reading on this build, peruse these articles on the cage and suspension installations.

Image courtesy of Wyatt Couch and Josh Smith

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