2006 Mazda MX-5 Miata Secifications
Engines: Light, compact, highly responsive, powerful MZR engines with appropriately sporty intake and exhaust notes were developed to assure that the MX-5 is brisk, nimble, linear in response, and very fun to drive. Based on the acclaimed MZR engine series installed in other Mazda models, these engines are front-midship mounted on the MX-5 and adopt the latest technologies developed to boost power appropriately for a lightweight sports car while supporting environmental compatibility with greater fuel-economy and reduced emissions.
Powertrain lineup by market
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Key features of the MZR family are aluminum block and head construction with iron cylinder liners, chain-driven double-overhead camshafts, variable intake-valve timing, electronically controlled sequential-delivery port fuel injection, and coil-on-plug ignition.
The compression ratio is 10.8:1 and both engines also share an 83.1 mm (3.27 in) stroke. The bore in the 2.0-liter engine is 87.5 mm (3.44 in) versus 83.0 mm (3.27 in) in the 1.8-liter engine. The range of intake valve opening and closing variability is 30 (camshaft) degrees. The bucket tappets have low-maintenance shims for lash control. Piston skirts are coated with a molybdic anti-friction compound.
Overall engine length was trimmed by 69 mm (2.72 in) compared with the second-generation model by thoughtful location of external components. Tilting the engine 10 degrees to the right provides room for a large, low-restriction Variable Intake System (VIS) with two operating modes to enrich the torque curve. VIS is tuned with an emphasis on odd and half-order harmonics at high rpm to provide a lively, robust engine note. MZR engines destined for Europe have swirl-control valves located in the intake manifold near the cylinder head interface to improve cold drivability and to reduce low-rpm exhaust emissions. A four-into-one exhaust manifold is positioned on the low (right) side of the engine block. Compared to the previous MX-5 intake restriction is lower by 57-percent and exhaust restriction has been diminished by 40-percent.
Peak output of the 2.0-liter engine for North America is 170 hp at 6,700 rpm with a manual transmission.
At least ninety percent of peak torque is available from 2,500 rpm to the 6,700 rpm redline. (The fuel cut-off is at 7,000 rpm.) Response has been tuned by use of a flywheel lightened by 0.3 kg (0.7 lb), a large electronically controlled throttle, and very rigid drive shafts.
Engine specifications (Provisional data)
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MZR 1.8 |
MZR 2.0 |
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| Transmission | 5-speed manual |
5-speed manual |
6-speed manual |
6-speed Activematic |
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| Displacement (cc) | 1,798 |
1,999 |
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Bore x stroke (mm) |
83.0 x 83.1 |
87.5 x 83.1 |
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Compression ratio |
10.8 |
10.8 |
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Max. output |
EU: 93kW (126PS)/ 6,500rpm |
NA: 170hp/6,700rpm |
NA: 166hp/6,700rpm |
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Max. torque |
EU: 167Nm/ 4,500rpm |
NA: 140lb-ft/5,000rpm |
NA:
140lb-ft/5,000
rpm |
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NA: North America , EU: Europe , JPN: Japan , AUS: Australia
Transmissions: The five-speed manual transmission is carried over from the second-generation MX-5 with key changes. To handle the additional torque, the inner structure of the transmission, the counter shaft, and third gear are stronger. Triple-cone synchronizers for first and second gears, double-cone synchros for third, and a carbon-type synchro for fourth reduce shift effort.
Gear ratios in the newly engineered six-speed manual transmission are purposely close to enhance the joy of sporty driving. Short, quick shift strokes have been achieved by use of triple-cone synchros on the first four gears. To reduce inertia, the third-fourth synchro is located on the counter shaft. For positive feel, the shift linkage is a single unit supported by low-friction bushings and guided by a steel plate.
As a convenience, reverse is located adjacent to first gear. Accidental engagement is prevented by the need to press down on the shift lever in order to select reverse gear.
A new Activematic automatic transmission adds a fresh dimension to the MX-5’s driving personality. Six ratios are provided with wide spacing in the interests of fuel efficiency. First gear is 31-percent lower than the second-generation MX-5 automatic to provide a very aggressive launch performance. Sixth gear is 21-percent higher for high mileage and quiet highway cruising. Steering wheel paddle shift is available in certain markets and models. Paddles mounted behind the steering wheel command upshifts while buttons positioned on the spokes are used for downshifts. Coordinating engine torque with the shift sequence results in smooth, seamless, and fast gear changes.
BODY RIGIDITY
As mentioned in Chapter 2, as a result of employing ultra-high strength and high strength steel sheet as well as advanced analytical technology, compared with the second-generation MX-5, bending rigidity has been improved by 22-percent and torsional rigidity by 47-percent. Additionally, the rear of the transmission is rigidly linked to the front of the differential housing by a Z-shaped power plant frame made of pressed aluminum. This assures that the driver’s throttle inputs are faithfully and promptly conveyed to the rear wheels, ensuring the maximum possible oneness between car and driver.
The high-mount backbone frame running along the top of center tunnel from the rear of the dash panel is joined fore and aft to the main frame in continuous closed section. This improves body stiffness and energy absorption during collisions without imposing significant weight penalties. Bolting lateral under-tunnel members directly to the seat anchor points enhances rider and horse oneness by minimizing seat flexibility and vibration.
STEERING AND SUSPENSION
DRIVING DYNAMICS
Whether it’s called JInba Ittai, rider and horse, or happy-face motoring, driving fun in a highly responsive open roadster is a cross-cultural experience that is appreciated in every corner of the globe. Mazda revived this simple pleasure with the launch of the original MX-5 in 1989. With the arrival of a third-generation roadster this year, Mazda engineers seized the opportunity to continue the best features from two previous models while adding new MX-5 dimensions to assure that Mazda’s Zoom-Zoom spirit continues to thrive in the 21st century.
Takao Kijima’s development team identified five core requirements for achieving of a fun-to-drive personality:
• Lightness
• Optimal weight distribution
• A priority on handling
• A consistently nimble, natural feel
• Dynamic-feeling performance.
The pursuit of the lightest possible weight and the advanced technologies selected to achieve a third-generation MX-5 that, in spite of being larger in nearly every dimension, is only about 10 kg (22 lb) heavier in base weight than the car it replaces are covered in detail in Chapter 2. This chapter will focus on the four other core requirements and the details of the chassis and powertrain components engineered to achieve them.
Optimal Weight Distribution
To insure that the driver’s control requests are faithfully and expeditiously fulfilled by the car, its weight should be balanced equitably between the front and rear axles. The optimum sports car has the lowest possible center of gravity (cg), the lowest possible moment of inertia in the yaw plane [major masses located closely to a vertical axis through the center of gravity], and half of the total weight of the vehicle and its occupants carried by each axle.
These principles guided the general layout and development of the MX-5. In spite of the new car’s slightly larger size, higher level of standard equipment, and its larger and more powerful engine, Kansei Engineering has allowed Kijima’s team to achieve the aforementioned core requirements such as the optimal 50:50 front/rear weight distribution.
To lower the yaw moment of inertia by two-percent with respect to the second-generation MX-5, major masses have been moved closer to the center of the car. For example, the engine is moved rearward by 135 mm (5.3 in), facilitated by an HVAC unit that’s seven-percent smaller than before and an extra 20 mm (0.79 in) of distance between the driver and passenger. Moving the battery—now changed to a standard type for lower maintenance costs—from the trunk to a new location ahead of the engine diminishes its distance from the cg by 265 mm (10.4 in). The fuel tank has been moved forward by 110 mm (4.3 in) and lowered by 120 mm (4.7 in) from its previous position in the trunk to a new under-floor location. The net change in the MX-5’s cg height is a worthwhile 18 mm (0.71 in).
Thanks to the JInba Ittai emphasis and Kansei Engineering strides, the new MX-5 sets an enviable standard in terms of light weight, cg height, and polar moment of inertia. A few sports cars do top it in certain categories: some are lighter, some have lower cg and lower moment of inertia, etc. But the development team believes that there is no lightweight sports car with the MX-5’s combination of design virtues capped by an affordable price.
A Priority on Handling
Clear and specific handling targets were established to assure that this attribute rose to the top of the requirements list. A particular emphasis was placed on achieving a brisk, nimble feel which sometimes causes diminished stability and undesirable sensitivity to external forces such as road irregularities and crosswinds. With this in mind, the development team sought a balance wherein the rear of the car maintains an unshakable grip with the road for maximum stability while the front of the car is solely responsible for initiating directional changes requested by the driver. To achieve highly consistent grip over various road surfaces and during changes in braking or power delivery, the development team selected highly linear control of the toe (steering) and camber angles as well as the vertical forces applied to each tire. At the rear of the car, a new multilink suspension system was selected because this approach offered the most freedom in selecting the ideal geometry for all wheel movements.
To minimize the amount the rear of the car rises during braking, front and rear suspension systems are configured to provide a strong anti-dive effect. Suspension links are arranged to convert a portion of the braking force fed into the body into a moment which counteracts the natural tendency of the body to pitch slightly down in front, up in back. Minimizing the dive movement also minimizes rear-wheel travel and unwanted changes in toe and camber. The net improvement over the second-generation MX-5 is a 38-percent reduction in dive during braking.
A similar technique is used to control the body’s tendency to squat during acceleration. Arranging the rear suspension links to provide an anti-squat effect again minimizes rear-wheel travel and unwanted toe and camber deviations. The net effect is 78-percent less squat than in the second-generation MX-5 and a more stable feeling rear grip that’s undisturbed by changes in throttle position or brake applications.
To achieve a feeling of nimbleness and willingness to change direction in response to steering inputs, the development team focused on achieving maximum rigidity throughout the steering system. The diameter of the steering rack was increased from 23 mm to 24 mm (0.91 in to 0.94 in) in the interests of higher stiffness, the torsion bar that opens the power-steering assist control valve is stiffer, and the pinion gear and control valve have been integrated into one assembly.
At the rear of the MX-5, the subframe that supports the differential and suspension links is attached to the unibody at six points so lateral forces result in minimal deflection. Together these measures help minimize the lag between steering input and car reaction.
Achieving a Consistently Nimble, Natural Feel
Competitive sports cars achieve excellent performance without necessarily providing a natural feeling of nimbleness in all driving situations. To raise the MX-5 above that level of achievement, a special group of test experts was assigned the task of applying Kansei Engineering to quantify subjective aspects of handling, to analyze these aspects in detail, and to find the means of providing a consistently nimble and natural feel in all driving situations.
As a first step, consistent performance character was defined as an operating feel through the steering wheel, accelerator, brakes, and other controls that is light and predictable in all driving situations. Also, all running, turning, and stopping movements should convey a feeling of nimbleness. To study these characteristics in fine detail, the team focused on six specific situations wherein any driver could experience the new MX-5’s signature nimble and natural handling:
• Entering a main road from a parking lot
• Turning at a road junction
• Driving through urban or suburban traffic
• Driving on winding roads
• Joining freeway traffic
• Passing on the freeway.
The team quantified nimbleness by plotting steering response versus steering effort for all MX-5 generations and various competitors in order to select a target point for the third-generation edition. Another measure documented and studied was the amount of change in the rate of acceleration (∆G) after the throttle was opened.
This same procedure was used to coordinate accelerator pedal, clutch, steering, and shift efforts. In each case, a consistency line was plotted and control variables adjusted to achieve a highly consistent feel throughout each driving operation.
Another important criterion for sporty driving is the lateral restraint provided by the driver’s seat. By studying the pressure distribution in the seat back and cushion, it was possible to improve the level of lower-back holdduring cornering. This index was also plotted versus steering gain (vehicle response speed to steering) and steering force as part of the consistency effort.
Dynamic-Feeling Performance
A key part of the desired lively feel is how a push of the throttle translates into forward acceleration. Initially there’s a surge followed by gradual convergence toward a steady forward acceleration. Making that convergence as rapid and as tight as possible greatly improved the MX-5’s sense of directness and liveliness. Increasing the stiffness of driveline components and reducing yaw inertia of rpm are obvious means of speeding this convergence. A computer-aided engineering system was very helpful in modeling, testing, and analyzing this aspect of driving. In practical terms, we shaved weight off of the flywheel, tuned the electronic throttle, further bolstered propeller shaft stiffness and optimized the engine mountings.
The engine’s ability to continue producing a strong flow of torque at very high rpm is another highly sought after sports car attribute. Mazda engineers call this “extensibility.” The requirement is a very flat torque curve with minimal wilt after the peak value. In the MX-5 various tuning measures were applied to achieve this important characteristic.
How the engine sounds is arguably the most critical phase of the sports car experience. Here a driving simulator was used to clarify the relationship between acceleration rate and engine sound. The team’s conclusion was that a harmonic, linear sound was most appropriate during acceleration. (Tuning the engine’s note through all operating regimes is discussed in full detail in Chapter 5’s Dynamic Craftsmanship section.)
Given the MX-5’s global reach, engineers spent ample hours in faraway places tuning and testing prototypes. There were four week-long trips to drive on US roads, a month spent evaluating winter performance in both New Zealand and Sweden , three visits to two Japanese race tracks, and nine trips to England and Europe . High-speed dynamics were studied on German autobahns. Nearly two weeks were spent exploring the ragged edges of the performance envelope on the 73-turn, 21 km (13 mi) Nurburgring Nordschleife circuit where the new MX-5 bettered the second-generation model’s lap time by 15 seconds.
BASE CURB WEIGHT
WEIGHT REDUCTION AS THE TOP PRIORITY
Mazda’s “Gram Strategy” - The Ultimate Weight-Saving Imperative
There’s a natural tendency for curb weight to rise when car manufacturers respond to market demands for more comfort, greater occupant protection, and better environmental responsibility. Realizing that this is contrary to the JInba Ittai goal and that extra weight has a dramatically negative influence on driving, cornering, and braking performance, Mazda engineers made every gram count. (In the English measurement system used in the US and elsewhere, one pound equals 454 grams.) Their “gram strategy” assessed weight in the smallest possible increments. For example, simplifying the rear-view mirror’s design trimmed 84 grams (0.19 lb). But applying this strategy throughout every nook and cranny of the MX-5’s design proved to be a very effective means of building a very light sports car that met all of its market demands.
Targets were set for the total vehicle’s weight—at 1,128 kg or 2,487 lb for the base MX-5—and also for the weight of individual parts and systems. All 16 Product Module Teams (PMTs) then set about designing the components they were responsible for with their weight targets firmly in mind. Major opportunities for saving weight by changing the decklid from steel to aluminum and the engine block from iron to aluminum were naturally accounted for in the initial targets. Only then, in order to close the gap between each PMT’s weight target and the weight of the components they were responsible for, was the gram strategy employed.
Mechanical prototypes were carefully scrutinized for every possible weight savings opportunity. More than 100 PMT engineers also examined three-dimensional models of the upper body and interior components in search of excess weight. Later, when completed running prototypes became available, they too were studied part-by-part, detail-by-detail for ways to trim weight one gram at a time.
Notebooks compiled list a total of 573 ideas representing a total of 43.589 kg (96 lb) that were considered as weight savings measures. Of course many were rejected as unsuitable from strength, reliability, or crash-performance standpoints. But a lot of ideas—like trimming metal flanges, eliminating excess quantities of lubricant and shortening the length of fasteners—were employed to achieve the MX-5’s ambitious weight target.
Well before the gram strategy was employed as a final measure to reach the weight target, the basic unibody was designed using high-strength, low-weight materials capable of delivering the desired rigidity and the lowest practical weight. Three fundamental weight-saving policies were: to use thin material in large cross-section structures within the wheelbase in the interests of high rigidity; to use the minimal amount of sheet metal in overhang areas; and to incorporate as much ultra-high-strength steel in the thinnest possible gauge to meet crashworthiness goals.
High-strength steel comprises 46-percent of the new MX-5’s body structure by weight. Twelve percent of the unibody is made of ultra-high-strength steel which has nearly three times the yield strength of ordinary steel. The net savings attributable to this approach is approximately 10 kg (22 lb). The complete body-in-white weighs 247.5 kg (546 lb) which is 1.6 kg (3.5 lb) less than the previous MX-5 in spite of major reinforcements added to improve crashworthiness and dimensional increases necessary to accommodate larger-stature occupants.
Use of aluminum for the hood, deck lid, power plant frame, front suspension control arms, rear hub carriers, rear brake calipers, and rear suspension spring seats trimmed additional grams. Furthermore, the new engine’s intake manifold and cam shaft cover are molded of lightweight composite-plastic materials. The block of the previous 1.8-liter engine was cast-iron while the new 2.0-liter engine has an aluminum block with thin cast-iron cylinder liners. With accessories added, the net weight savings attributable to the engine alone is a substantial 19.1 kg (42.1 lb).
Mounting the power steering pump and the air-conditioning compressor directly to the engine block eliminated separate brackets weighing 3.2 kg (7 lb). Using a hollow tube instead of a solid rod for the front anti-roll bar trimmed another 2.4 kg (5 lb). Use of aluminum pipe and optimization of fixed structures in the steering system achieved another 0.6 kg weight saving.
High-strength steel has also been specified for seat backs and cushion side frames yielding a net savings of 4.8 kg (10.6 lb).
The gram strategy also met success in brake and steering systems.
In final form, the new MX-5 is larger, more powerful, more capable, more comfortable, and more useful. It offers several new features and greatly improved occupant protection from collision injury. Yet, thanks to Kansei Engineering and Mazda’s gram strategy, the MX-5’s base curb weight is only increased by approximately 10 kg (22 lb).
While saving weight is a top priority for achieving JInba Ittai, because a lower weight improves every aspect of performance including fuel efficiency. Other concerns were the stiffness of the unibody structure, the height of the car’s center of gravity, 50:50 weight distribution, and the MX-5’s moment of inertia about a vertical (yaw) axis. (A lower yaw moment of inertia quickens the vehicle’s responsiveness to the driver’s steering commands.) Each of these parameters strongly influences the final design’s overall fun-to-drive characteristics.
A stiff body structure is an essential ingredient in the feeling of oneness between the car and its driver. Thanks to shrewd analysis and the application of advanced materials, the new unibody is 22-percent stiffer in bending and 47-percent stiffer in torsion compared to the previous MX-5.
Moving the engine rearward by 135 mm (5.3 in) was a major step towards balancing front-to-rear weight distribution and reducing the yaw moment of inertia. Both the battery and the fuel tank were shifted forward to new locations closer to the center of gravity. The fuel tank was also lowered substantially. Slanting the top of the radiator forward also helped lower the center of gravity. The MX-5’s total yaw inertia is reduced by a significant two-percent.
With two occupants on board, each axle carries approximately 50-percent of the load (50:50 weight distribution). (Fully loaded with fuel and luggage, the rear wheels carry slightly more weight than the front wheels. At curb weight—no driver, no luggage, full fuel tank—there is a slight weight bias in favor of the front wheels.)
World’s First Friction Stir Spot Welding between Steel and Aluminum
One example of advanced technology employed to save weight is spot friction welding used to join steel stud plates to the MX-5’s aluminum decklid panels.
It is normally difficult to join aluminum and steel by welding. To overcome this problem Mazda developed new welding technology that employs a special high-speed spinning tool. As the blade edge of the welding tool spins and comes into contact with the aluminum, the heat generated by plastic deformation of the aluminum softens the steel sheet directly beneath. Continuously applied pressure removes the zinc plating from the surface of the steel sheet, bringing the aluminum and steel sheet into direct contact and joining them. The zinc serves to prevent bimetallic corrosion that normally occurs at this point. Thanks to this spot friction welding technique, the large current used in resistance spot welding is not required, and each weld is completed in a few seconds. Mazda engineers have applied for 20 patents to cover this innovative technology and expect to use it extensively in the future to achieve worthwhile weight savings in other vehicles.
2006 Mazda MX-5 Overview2006 Mazda MX-5 Chassis Details
2006 Mazda MX-5 Exterior/Interior Details
2006 Mazda MX-5 Safety, Security Environmental Details
2006 Mazda MX-5 Special Features
2006 Mazda MX-5 Specifications
