We compared Lexus RX engines, and the efficiency crown goes to…
Lexus has never been big on diesel engines, and prefers to offer petrol-hybrid powertrains as their alternative power units instead. In the case of the Lexus RX luxury SUV, that means a choice between two V6 engines, optimised for either petrol-only propulsion or for hybrid assistance. Which one gets the efficiency crown?
The Lexus RX can be had in short- or long body formats: the latter with the same wheelbase as the shorter one, but with about 100 mm added to its rear overhang to allow a third seating row. However, the hybrid variant is only available in high-spec trim and with the standard 5-seater layout, so we selected a petrol 5-seater with similar specifications to maintain a level playing field.
For this article, we evaluated efficiency based on two parameters: their claimed (official) average fuel consumption, and their power-to-weight ratios. The former is self-explanatory; while the latter refers to the power output, relative to the car’s kerb weight, expressed in kW/ton and used as an indication of the car’s potential performance.
Lexus RX 350 F-Sport (R 1 225 800)
Outputs: 221 kW and 370 Nm
Claimed Average Consumption: 9.6 ℓ/100 km
Power-to-weight ratio: 106 kW/ton
This engine and 8-speed gearbox combination is used in most Lexus RX variants, but the F-Sport comes closest to the hybrid version in terms of standard equipment (and thus equalises the weight difference as far as possible).
It is immediately apparent that the “350” powertrain makes for quite a thirsty beast with its average consumption of 9.6 ℓ/100 km, so should probably not be the first choice for buyers who keep an eye on their fuel budget. The power-to-weight ratio of 106 kW/ton should satisfy most buyers’ performance requirements, however.
Lexus RX 450h SE (R 1 424 500)
Outputs (system total): 230 kW and 335 Nm + 139 Nm (electric)
Claimed Average Consumption: 5.7 ℓ/100 km
Power-to-weight ratio: 104.7 kW/ton
Employing the same 3.5-litre V6 engine but in a much lower state of tune, the RX 450h relies on electrical assistance to boost its outputs beyond those of the petrol-fuelled RX 350 variants. The peak power output isn’t much different at 230 kW (vs 221 kW), but the electric motor can add up to 139 Nm to the petrol engine's 335 Nm, giving a wider torque spread.
The hybrid system’s weight penalty is also smaller than might be expected (125 kg), making for a power-to-weight ratio that’s only marginally lower than the petrol-only car’s. In combination with a CVT (Constantly Variable Transmission), this torque advantage gives the hybrid version a slightly quicker 0 – 100 km/h sprint time (7.7 seconds against 8.0 seconds), along with a vastly lower claimed average consumption of only 5.7 ℓ/100 km.
Verdict
With all things considered, the Lexus RX 450h has to take the efficiency crown: not only is it claimed to be slightly quicker in a straight line, but it is also supposed to use a lot less fuel than the RX 350 F-Sport. In fact, we achieved lower fuel consumption in a real-world test with the RX 450h than the RX 350’s claimed figure, so its advantage isn’t mainly theoretical. Quicker and more parsimonious, the RX 450h emerges as the winner over its more-conventional sibling.
* Prices include all taxes and were accurate at the time of writing, but may change without prior notice.
