How a 1.5L engine uses Formula One logic to defy physics
In short: Engineering a long-stroke engine usually invites high-frequency vibrations that can tear a motor apart. Yet, Toyota solved this by borrowing a high-performance secret from the racetrack, allowing a compact car engine to reach racing-grade speeds without the typical mechanical penalty.
The Toyota SZ engine family utilizes a sophisticated 'Desaxe' crankshaft design, which offsets the crankshaft center from the cylinder centerline. This mechanism is engineered to enlarge the intake and expansion strokes while simultaneously reducing piston side-load during the expansion stroke. By optimizing these movements, the engine achieves superior thermal and mechanical efficiency, particularly during partial-throttle conditions where it can operate on a Miller cycle.
A standout example of this engineering is the 1.5L 3SZ-VE engine. Because it is a long-stroke design, it naturally faces secondary imbalance vibrations. Toyota addressed this by using exceptionally lengthy connecting rods, which measure 18.5mm further between centers than those of the 1.3L 2SZ-FE. This increase is more than 50% greater than the standard increase required to match the stroke, a design choice comparable to Formula One and other racing engines.
To accommodate these oversized rods, engineers increased the engine's deck height by 25.5mm. This structural adjustment allowed the 3SZ-VE to maintain a 6,500rpm redline, identical to the smaller 1.0L and 1.3L variants despite having a vastly different bore-to-stroke ratio. The package is further refined by a thin-wall cast-iron block produced via a 'Cold Box' method, achieving 3mm-thick walls to keep the bare engine weight at just 68 kg.
The family also features narrow-angle valves (18.6° stem-to-stem) and variable valve timing (VVT-i). In the 1.5L variant, the intake valve size was increased to 27.8mm to handle higher flow volumes, necessitating the use of small 12mm spark plugs. This combination of racing-inspired rod geometry and precision casting allows for a compact, high-revving powerplant suitable for everything from daily commuters to rally homologation specials.
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- Summary by Intellect · source: Toyota SZ engine
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