Driving Economically.

Joe_Horner

Delivery_Driver wrote: »

What happened to torque and power crossing at 5252 rpm in that graph?I'm not nitpicking, just wondering if there is some reason for it?

That 5252rpm figure only holds for lbft and BHP, if you change the units (in this case NM and kW) you change the crossover because of the different constants involved in converting.

Simple way to imagine that is if you just changed one of the units in the above graph and plotted torque in lbft against power in Nm. Even though it's strongly not recommended to mix units from different systems there's nothing actually "wrong" with doing so.

So:

1nM = 0.7376lbft so all of the values on the torque curve would reduce to about 3/4 of their value - ie: the whole curve would "drop" vertically on the graph.

The power curve would stay as it is.

So the crossing point would shift even lower in the rec range to (at an eyeball guess) about 2250RPM

Delivery_Driver

I did wonder if it was because it was metric.I can convert them but always think in bhp and lbft really.

mikey72

I suppose actually this thread started out on diesel HGV's, which don't have a throttle to restrict the airflow. (Apart from egr valves nowadays, and the technology with them).
So does full throttle still work out best, or do you just get a nice cloud of black smoke?

Notmyrealname

I use full throttle in my Mondeo and it works out fine but thats diesel too

Joe_Horner

mikey72 wrote: »

I suppose actually this thread started out on diesel HGV's, which don't have a throttle to restrict the airflow. (Apart from egr valves nowadays, and the technology with them).
So does full throttle still work out best, or do you just get a nice cloud of black smoke?

You just get a cloud of black smoke

More seriously, I've never looked too closely at diesels so I'm honestly not sure what would offer best economy with them, but you've given me something new to investigate

mikey72

Joe_Horner wrote: »

You just get a cloud of black smoke

More seriously, I've never looked too closely at diesels so I'm honestly not sure what would offer best economy with them, but you've given me something new to investigate

The other thing to look at on petrols now, when you accelerate you don't actually do anything other than move a potentiometer.
So the ecu looks at the rate of change, the start and stop positions, if it's a fast rate of change, and to the end stop, it uses a performance map, if it's a slow rate of change, and not to the floor, it uses a more economical map, so another variable in the overall equation.

Joe_Horner

mikey72 wrote: »

The other thing to look at on petrols now, when you accelerate you don't actually do anything other than move a potentiometer.
So the ecu looks at the rate of change, the start and stop positions, if it's a fast rate of change, and to the end stop, it uses a performance map, if it's a slow rate of change, and not to the floor, it uses a more economical map, so another variable in the overall equation.

Fair comment on the rate of movement. Maybe I should have been more specific earlier - flooring it doesn't need to mean stamping on the pedal, you can (and should for the car's sake) open it fully but smoothly. Don't pull the trigger, squeeze it

thor

Notmyrealname wrote: »

6) Driving around town. Now this sounds completely counter-intuitive but isn't. In most cars, driving in 4th gear at 30MPH is too high a gear.

Most of the points I regard as common sense but this one completely threw me. I have been driving around town in 4th and even 5th gears. How much extra petrol would I have burned?

Delivery_Driver

You need more throttle at low speed in higher gears, wasting fuel.It depends on the gearing of the vehicle you are in but I find 30mph in 4th generally ok for mine.

Notmyrealname

thor wrote: »

Most of the points I regard as common sense but this one completely threw me. I have been driving around town in 4th and even 5th gears. How much extra petrol would I have burned?

It depends on the gearing of your car and the type of traffic and roads. Its mostly when you're in areas where you're going to be varying speed a lot. How much extra depends on the vehicle.