Smaller displacement engines with high specific torque and boost levels require fast transient response,
especially at low engine speeds, in order to be a valid replacement for larger displacement engines.
In practice, this means a combination of superior torque
at low engine speeds with an ongoing surge of power and performance up to the higher speed range.
This allows for a more aggressive engine start - stop system, and the electric motor provides a power
boost at low engine speeds, improving acceleration.
To provide back - up for the mechanically driven coolant
pump at low engine speeds and to ensure adequate coolant circulation.
The hydraulic system is designed to guarantee fully closing the engine valve at the maximum engine speed such that early valve closure
occurs at lower engine speeds.
These features all combine to provide the perfect balance between power and economy with good torque being
delivered at low engine speeds to provide a great urban drive.
A small, quick - responding turbo feeds air to the combustion
chambers at low engine speeds to provide low - speed torque and eliminate turbo lag.
This is achieved by providing reduced intake valve lift and
duration at low engine speeds for good torque, with increased intake valve lift and duration at higher rpm for optimum power.
This offers the right balance between ride comfort, reduced consumption and sporty character, performing smooth gear
changes at low engine speeds.
During the closing stage of the engine
valve at lower engine speeds, only a part of the spring potential energy is utilized to empty the cylinder by discharging the oil; the rest is wasted.
This gives the turbocharger the response of a smaller
turbo at low engine speeds with the power of a bigger turbo at higher engine speeds.
In addition to increasing with engine size, the torque output also characteristically
comes at lower engine speeds for better accelerator response.
Supercharging is preferred to turbocharging because of the engine's high compression ratio, which means it won't take high torque
levels at low engine speeds.
Minor turbo lag is
evident at low engine speeds despite the torque peaking at rather mundane rpm, and the electronic power steering and shifter leave some room for improvement in terms of feel.
The result is a system that provides the advantages of both a small and large turbocharger, improving flexibility and acceleration,
particularly at low engine speeds.
Some engines are designed to open each intake valve at a slightly different time, which increases turbulence, improving the mixing of air and
fuel at low engine speeds.
The engine's Variable - length Intake Manifold (VIM) switches between a long intake
manifold at low engine speeds and a short intake manifold at higher engine speeds.
The key here is the German car's higher
outputs at lower engine speeds, and an eight - speed automatic transmission that does a better job than the Mazda's six - speed unit of keeping its engine in the torque zone.
The damper enables first range lock up, delivering significantly more lock up operation and operating
at lower engine speeds in higher ranges to further improve fuel economy.
Things change during moderate - speed cruising and
at low engine speeds when the rear bank of cylinders shuts down to effectively create a three - cylinder powerplant.
Earlier 16 - valve Toyota engines suffered from a lack of
power at lower engine speeds, but mechanical and electronic improvements have spread the power and made the vehicles peppier off the line.
Peak power climbs from 641bhp to 710bhp, torque from 500 lb ft to 568 lb ft and both outputs are
produced at lower engine speeds — 7000rpm for the former (250rpm lower than a 650S), while the latter is available between 5500 and 6500rpm compared to the 650S where torque all arrives at 6000rpm.
Electronically - controlled valves close off two
pipes at lower engine speeds, then open up to unleash the full - blown hellish din at full throttle and crackles under deceleration.
This trick to improve response will also be seen in the Bugatti Chiron — with two turbochargers doing the
work at lower engine speeds and all four as engine speed increases.