Brake Specific Fuel Consumption (BSFC) Maps

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Brake Specific Fuel Consumption Maps

Useful for determining at what load and rpm your engine is making the most power out of the fuel given to it.

Cummins 5.9L B5.9-175 diesel

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Cummins 5.9L ISB-235 diesel

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1st Gen Honda Insight 1.0L

CVT, which would have lean burn if the car tested was a Japanese-market Insight. Electric assist does not appear to have been accounted for, so the high-load, high-RPM BSFC is grossly underestimated.

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On a chassis dyno with a lean burn capable manual transmission equipped vehicle, with no evidence of reduced BSFC at the low load, low RPM regime where lean burn operates:

Mercedes Benz 300SD OM617 5 cylinder turbo diesel

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MG 1.8L B-Series

BSFC map generated from the information below.

Saturn 1.9L DOHC Modified

Saturn 1.9L BSFC: Included imperial units, Constant Horsepower curves, Engine Load %, and extrapolated to redline.

Approximate Vacuum readings on Magenta Optimum Efficiency Line:

6.7"hg at 1000 rpm

6.5"hg at 1500 rpm

5.7"hg at 2000 rpm

5.0"hg at 2500 rpm

3.8"hg at 3000 rpm

2.3"hg at 3500 rpm

1.3"hg at 4000 rpm

0.9"hg at 4500 rpm

0.2"hg at 5000 rpm

WOT at >5100 rpm

Subaru EJ22 2.2L SOHC

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Toyota Prius 1.8L 2ZR-FXE 2010-

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Volkswagen 1.4L TSI

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There was an article on VW's cylinder deactivating TSI in a magazine (Serwis motoryzacyjny, 11/2011) and it had the following BSFC graph, illustrating an example of how cylinder deactivation can help reduce fuel consumption.

The red line '1' graphs constant engine power, in this example 30kW. By going to an rpm and load closer to the BSFC sweetspot the fuel consumption can be lowered by 20%. Deactivating half of the cylinders helps to increase the load, but among the things the article didn't state are: Is that BSFC for the engine in 4-, or 2-cylinder mode? Or maybe combined? What would be the effect of only shifting gears? What would be the effect of only deactivating 2 cylinders?

Anyhow, the article claimed that only deactivating the cylinders reduced fuel consumption by 0.4 l/100km in the NEDC cycle, while with the Start/Stop system 0.6 l/100km. At steady, low speeds and loads the fc can be reduced by 0.7-1.0 l/100km. The cylinders are deactivated when engine speed is between 1400 and 4000 rpm, and torque between 25 and 75 Nm (the max torque is 250 Nm).

Volkswagen 1.5L diesel

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Volkswagen Jetta TDI 1.9L ALH 1999.5-2003

Each curve represents a constant horsepower developed by the engine. If you are driving on a given road with a constant grade, speed, and ambient conditions, regardless of which gear you are in, it requires roughly the same amount of power to overcome aerodynamic drag, rolling resistance and driveline losses. Therefore, regardless of what gear you're in, you're riding anywhere along the same blue curve; exactly where you sit on that blue curve being only dependent on the gear you're in and therefore the RPM at which the engine is turning over.

In the case of the TDI BSFC chart, if I take the example of operating on a certain speed such that the power is 20 HP, the lowest BSFC occurs when running at the gear that corresponds to about 1250 RPM. If I run at either a higher- or lower RPM from this point, my BSFC will increase. This is about the only point in the entire engine map where it would be disadvantageous to operate at an even higher gear if one were available (lower RPM) because of the worsening BSFC. Almost everywhere else, the lowest BSFC is achieved at the lowest possible RPM at a given power.