POWER AND PERFORMANCE - MZR 2.3L DISI TURBO ENGINE

Mazda's MZR 2.3-litre DISI (Direct Injection Spark Ignition) Turbo engine is Zoom-Zoom in its purest form. Currently found in the Mazda6 MPS and Mazda3 MPS models and now in the all-new CX-7 crossover SUV, it was created by Mazda's engineers to deliver ample power and torque by employing dual overhead cams, four valves per cylinder, turbocharging and intercooling. And as if this wasn't enough, they also developed one of the first direct fuel-injection systems available in the SUV segment.

Employing a different turbocharger to the version used in the MPS models boosts low-speed torque delivery, with the CX-7's engine producing 175kW at 5000rpm and 350Nm of torque at just 2500rpm.

Squirting fuel directly into the combustion chamber is not a novel idea. All diesel engines use this type of fuel delivery, and piston-engined fighter aircraft began employing direct gasoline injection to ensure consistent performance when inverted flight was necessary during aerial combat. Direct injection came to motor sports in 1954, allowing competitors to eke out every last horsepower and mile-per-gallon for endurance racing - it's now considered an essential component in the design of competition engines.

In order to make an internal combustion engine run, liquid gasoline must first be converted to a vapor suitable for combustion. In most engines, fuel injectors operating at 40 or so psi spray atomized droplets into the intake manifold. But in the MZR 2.3 DISI Turbo, pressure is raised to 1,600 psi and the spray is directly into the cylinder. As a result, fuel droplets are significantly smaller. When exposed to air in the combustion chamber, these droplets instantly vaporize. That change of state (liquid to gas) absorbs heat from the surroundings.

Absorbing heat just before combustion is beneficial to any engine's health and well being. Cooling the intake charge raises its density, allowing more air to fit in a given space. More air yields more power. A cooler fuel and air mix is also less prone to detonation. That in turn facilitates a higher compression ratio and additional boost in turbocharged or supercharged engines.

Relocated fuel delivery allows intake ports to be optimized for air flow instead of air and fuel delivery. The MZR 2.3 DISI's intake ports are positioned higher and run straighter with the injectors located downstream.

Injecting an atomized spray of fuel directly into the combustion chamber also causes a richer mixture to form around the spark plug, which prevents misfire. With less likelihood of misfire, the ignition timing can be delayed following a cold start to maximize exhaust gas temperature. Hotter exhaust delivered to the catalytic converter speeds its warm up. Bringing the catalyst up to light-off temperature as quickly as possible is the key to ultra-low exhaust emissions.

Squeezing the air-fuel mix harder with a high compression ratio pays off later in the four-stroke cycle. In most engines (including MZR 2.3 DISI), the compression ratio is identical to the expansion ratio. During the expansion phase, combustion energy is delivered to the crankshaft on its way to the wheels. With more compression there's more expansion and extra power from every increment of gasoline.

To recap, direct fuel injection enhances Zoom-Zoom in several ways. It cools the intake charge and increases its density to build a bigger fire in the combustion chamber. Cool conditions also allow higher compression and extra turbo boost. In the case of Mazda's MZR 2.3 DISI Turbo engine, low- and mid-range torque is enhanced by 10-percent because of the 9.5:1 compression and expansion ratios. Beyond 2,500 rpm, 15.6 psi of boost does an excellent job of stuffing the combustion chamber and ripping the power curve.

Creating the DISI Turbo engine involved more than just changing the injection system and adding a turbocharger. The form and materials used for the major components are optimized to bear the added load and heat of the increased output. The aluminum cylinder block and cylinder head are made using a new implementation of the Mazda Advanced Precision Casting process, which increases their strength. In addition, cross drilling between the cylinder liners and between the valve bridges in the head improves coolant flow and heat resistance. The crankshaft and connecting rods are made of forged steel, wrist pins are a new full-floating design, connecting rods have an optimized shape and larger journal size, and pistons are designed for maximum stiffness and durability.

Direct fuel injection, in combination with electronic throttle control, is the most precise way to regulate an engine's speed and load.

Mating to a slick-shifting Aisin-sourced Activematic six-speed transmission with manual control, the CX-7 returns an economical 11.5L/100km on the ADR 81/01 fuel test.

The CX-7's advanced transmission and Active Torque-Split All-Wheel Drive components pass the engine's power cleanly to the pavement.

The AWD system uses a computer-controlled coupling integrated with the rear differential to deliver up to half the available torque to the rear wheels on demand. Sensors monitor engine information, individual wheel speeds, Anti-lock Brake System (ABS) operation, and the CX-7's standard Dynamic Stability Control (DSC) system to optimise torque distribution. Whether the driving conditions are dry and fast or slippery and moderately paced, exceptional handling is assured.

CHASSIS HAS MAZDA SPORTSCAR DNA

A light, stiff unibody provides the sound foundation for CX-7's smooth ride and agile handling. Computer-Aided-Engineering analysis was used to optimize this structure, delivering high torsional and bending rigidity with minimal weight.

In front, a perimeter frame mounted to the unibody through six rubber isolators supports the powertrain, the engine-speed-sensitive rack-and-pinion power steering and a low friction MacPherson strut suspension system, that employs a ball-type strut and lateral force control spring for smooth steering feel and ride comfort.

The multilink rear suspension consists of one trailing arm and three lateral locating members per side. To minimize cargo-compartment intrusion, the rear spring is positioned between the lower lateral member and the cross member that anchors rear chassis hardware to the unibody. The damper is located between the wheel hub and the unibody to provide excellent motion control with minimal friction.

All CX-7's are fitted with 235/60R18 tyres mounted on stylish 18 x 7.5J inch aluminum wheels. A robust 205/80R16 inch spare tyre is also provided.

A stiff body, with localized strengthening as well as the suspension subframes and noise reducing foam strategically located in 12 "noise paths" has ensured that CX-7 has low NVH levels transmitted from the tyres, road or engine.

The power steering system, which requires 2.9 turns lock to lock is similar in its setup to the Mazda6 and Mazda3 with it using a rigid aluminium housing, mounted on four rubber bushings.

Mazda's DNA requires that its vehicles provide responsive, linear brakes with good stiffness and the CX-7 achieves this by employing 296mm ventilates discs at the front and 302mm ventilated brakes at the rear. They are controlled by an ABS anti-lock system that incorporates Electronic Brake force Distribution and Emergency Brake Assist.