machine V6 Overview mazda

The V6 configuration appears in 1.8, 2.0, 2.25 and 2.5 litre displacements.
- 2.25V6 - worlds only Miller-Cycle (MC) as opposed to Otto-Cycle engine, using an 8 to 1 compression ratio with 10 to 1 power ratio for improved power to fuel consumption ratio. The MC uses a twin-intercooled Lysholm-screw Autorotor supercharger (the worlds most compact & most efficient) to deliver 210-230lb/ft at 3500rpm with 0-60 of 7.9secs from the 4-speed ATX, power of a 3.2-3.5V6, yet fuel economy of a 2.1V6.

- 2.5V6 - two variations of the 2.5V6 exist, as well as a Twin-Turbo form. The KL form is a detuned variant of the KL-ZE, offering power & fuel economy of a 2.2V6 (based on output of the 2.0V6). The KL-ZE is the 200bhp sports 2.5V6, achieving up to 94bhp/litre without expense of VVT.
Picture Courtesy of Dimas (Sephiro), 94 Ford Probe GT

- All V6s - all Normally Aspirated V6s feature a Variable Resonance Intake System (VRIS), the same concept as later used by Porsche on their 3.6 and Ferrari in much more sophisticated form on their V12. VRIS was first used by Mazda in their older 158bhp 2.0i-16 UK engine in 1989 and ensures the widest possible area under the torque curve rather than a purely headline peak figure. The VRIS efficiency contributes to the V6s noted low fuel consumption, with the 7500rpm (2.5) or 7800rpm (2.0) limits rarely being called upon, and averages of 27-29mpg (imperial) in urban driving and up to 32-36mpg (imperial) highway being the norm.

Engine Architecture
V6 engines are all-alloy DOHC 24V 60-degree-V6. A split-crankcase (as 911 flat-6) is used offering exceptional rigidity over traditional bearing-cap solutions and not only to high-rpm capability as proved in SuperTouring Car racing in up to 430-480bhp N/Aspirated form, but also reducing NVH data to set a benchmark in 1992 winning German engine awards. Bearings are four 4-bolt mains, with a further pair of bolts at each bearing section, key journals & bearings are oversized, bearings themselves are triple-layer heavy-duty spec. Crankshaft is forged, nitrided, triple-lapped, mirror finished. Piston squirters in upper bearing journals aid cooling. Exhaust valves are stainless steel. Pistons & rods are lightweight to reduce reciprocating mass, and the very short-stroke design aids longevity considerably. Piston skirts are Moly coated.

Piston & ring velocities are lower than those for the I4 engines. Quantitatively, the 2.5V6 Mean Piston Speed (MPS) is a very low 3170ft/min at redline and the 2.0I4 MPS is 3928ft/min at redline, the V6s very short stroke producing low crank angles thus minimising main & rod bearing load. For rings the 2.5V6 uses 1.5mm top ring allowing a Maximum Piston Acceleration (MPA) of 77,000ft/sec^2, yet the engine at redline experiencing an MPA of only 51,354ft/sec^2. The 2.0I4 uses a 1.17mm top ring allowing a Maximum Piston Acceleration (MPA) of 105,000ft/sec^2, with the engine at redline experiencing an MPA of 70,157ft/sec^2. Both engines have exceptional design margins, the V6 is particularly under-stressed even in KL-ZE form.

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