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In the course of an old fogey's refresher driving lesson, a year ago,
the Instructor explained the benefits of driving at the optimum rpm – not something that had occurred to me previously. I was then driving an Audi A4 (1800cc) and, in 5th gear, the recommended rpm of 2,500 gave a speed of around 56mph. I am now driving a Honda Jazz (1,400cc) - the previous, not the latest model - and 2,500rpm gives me around 53mph. Does this imply that, with this engine size, there is a different recommended rpm? I am trying to drive more economically now but, on the motorway, 53 is too slow to make much
progress, not being a member of CLOG.
the Instructor explained the benefits of driving at the optimum rpm – not something that had occurred to me previously. I was then driving an Audi A4 (1800cc) and, in 5th gear, the recommended rpm of 2,500 gave a speed of around 56mph. I am now driving a Honda Jazz (1,400cc) - the previous, not the latest model - and 2,500rpm gives me around 53mph. Does this imply that, with this engine size, there is a different recommended rpm? I am trying to drive more economically now but, on the motorway, 53 is too slow to make much
progress, not being a member of CLOG.
Asked on 27 June 2009 by
Answered by
Honest John
An engine will develop it maximum slogging power (torque) at between around 1,500rmm and around 5,000rpm depending on type of engine and fuel. Maximum 'horsepower' is usually developed higher in the rev range at between around 4,000rpm and around 6,000rpm. You can feel the torque best in a turbodiesel because they usually peak at between 1,750rpm and 2,000rpm with very little on offer below that so maximum torque arrives with a sort of catapult effect. If you drive at close to maximum torque you will get the best response from the engine without changing gear if you need to accelerate. Your old model Jazz 1.4 manual develops 83 horsepower at 5,700rpm and 119Nm torque at 2,800rpm. It is geared at 19.8mph per 1,000rpm in 5th. So it will be happiest and most efficient at 55 - 60mph.
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