BSFC (brake specific fuel consumption) explained

[teoman]

A friend did a quick demo with his vagcom. There was a torque reading there.

Torque vs rpm vs fuel in g/s would provide a good map?

Not sure how the torque is calculated or if it is measured.

[teoman]

I have some data now if anyone is interested in collaborating.

[hat_man]

OK, for the not so smart guy (me) in the room.

Someone suggested an indicator showing different colors representing the BSFC "islands" as a visual reference to help keep the driver in a better FE range (speed/rpm). Would an old school vacuum gauge do the same thing? Or is my confusion showing again?

[teoman]

That is one indicator.

[redpoint5]

Originally Posted by hat_man

Someone suggested an indicator showing different colors representing the BSFC "islands" as a visual reference to help keep the driver in a better FE range (speed/rpm). Would an old school vacuum gauge do the same thing? Or is my confusion showing again?

I'm not so sure such a visual would help. A driver needs to travel a particular speed, and the only variable to maintain that speed is which gear they are in. Generally, you want to be in the tallest gear that will allow you to maintain speed.

Engines produce a certain amount of power at a certain torque and RPM. In fact, horsepower is torque * RPM / 5252

The reason that the BSFC map isn't that useful is that it doesn't factor in the other variables such as increasing wind resistance due to traveling faster. It simply shows the most efficient RPM and throttle position (torque) to produce a given amount of power.

MPG or liters per 100 km is a better measure of efficiency because it factors in all of the variables.

So, BSFC is a good tool for engineers, but MPG is the right tool for drivers.

[teoman]

True, but having the chart and where you are at would enable you to make the proper adjustments without trial and error.

[redpoint5]

Absolutely, which falls more under the category of engineering than driving. The more extreme ecomodders here would use BSFC to inform their designs, but the casual eco drivers here would not have use for the info.

[sendler]

An instantaneous fuel economy vs acceleration gauge would be helpful for those of us that use PulseNGlide to use the best throttle opening position during the pulse. And help us choose the best gear for slower speeds while traveling through slower city streets.