The BSFC chart thread (post 'em if you got 'em)

[MGB=MPG]

linkback reference and credit
fair usage

The MG Experience: Library: Power, Torque and Consumption Curves



RPM Torque BHP Fuel Consumption MPH Fuel Consumption fuel consumption
(Lb.Ft.) (Pints BHP/hr) 4th gear [pints/hr] [pints/mile]
1000 71 0.95
1500 89 26 0.78
2000 101 38 0.69 36 26.22 0.728
2500 107 51 0.63 45 32.13 0.714
3000 110 63 0.58 54 36.54 0.676
3500 108 73 0.57 63 41.61 0.660
4000 106 81 0.575 72 46.57 0.647
4500 104 88 0.59 81 51.92 0.641
5000 98 94 0.62 90 58.28 0.648
5500 91 95 0.65
6000 92 0.73
http://www.mgexperience.net/article/...MGBGT_1966.pdf

[Hubert Farnsworth]

I know the original topic is a bit old now, but the top curve represented the wide open throttle torque, and each of the islands represents different part open throttle curves shown in contour format which is a way of referencing 3 dimensional data in a simplified two dimensional format.

The BMEP is a function of the work done per cycle divided by the displacement volume of the engine, and is a way of converting power in Kilowatts into the non displacement dependent variable of pressures which in an ideal engine would scale perfectly without regard to displacement.

The reason BMEP and Torque are sometimes interchanged the labled axis of the BSFC charts has to do with the fact that BMEP can be derived from the equation 2*Pi*Torque*Z / Displacement volume (for metric units in N-m for torque, and meters cubed for displacement) (Z=2 for four stroke engines and 1 for 2 stroke engines) BMEP can also be described as normalized torque.

Brake specific fuel consumption is based on the mass flowrate of the fuel divided by the power output of the engine in metric that becomes grams per kilowatt-hr.

[briank]

Am i right to say that one should open the throttle over a period of 2 second, instead of an instantaneous "blip", as I understand a blip (opening in less than 1 second/or high pedal angular velocity) also causes fuel enrichment for the duration of the blip.

It would be nice if the % throttle opening values could be mapped to % depression of the accelerator pedal, as I understand many manufacturer don't use a linear relationship (in drive by wire) of accelerator pedal depression vs throttle opening. i.e. a 20% pedal depression may equate to 40% throttle opening. This may be done so that the car appears more powerful to an unsuspecting customer.

Just me 2 cents.

[RRC]

Here is a power/torque/bsfc chart for Skoda Felicia with 1.3 MPI engine:



Click on it to resize

[oldbeaver]

Hello, these chart must be very useful, I guess. Can you please give us all a small intro to understand what are they and what is their importance?

Tks a lot for yr contribution.

[bwilson4web]

Originally Posted by oldbeaver

Hello, these chart must be very useful, I guess. Can you please give us all a small intro to understand what are they and what is their importance?

I will share my understanding in the hope that others may provide more details.

The Brake Specific Fuel Consumption measures how much power is provided versus fuel consumption of an engine in a test stand with the throttle wide open. The engine rpm is controlled by how much resistive force is applied. There are no accessory loads, not even water pump. It is a map of the best-case engine performance.

This chart can be used to find the optimum, rpm-power bands. In theory and practice, one could drive to stay in the peak efficiency band and maximize fuel economy. But a lucky few can do in-car measurements.

To do an in-car measurement, one needs:

• engine torque
• engine rpm
• fuel consumption

Usually torque is the problem but a few cars have them.

The product of engine torque and rpm is the power. Fuel consumption can be measured by mass air flow (14.7 to 1 air to fuel ratio) or fuel injector timing adjusted for the 'dead time.'

Once the data is collected and plotted, we can find inflection points, the knee or sometimes curve in the graph that identifies the optimum engine operating range(s). For example:

• 0-<980 - engine off, hybrid mode, very good
• 980-1200 - engine idle during warm-up, avoid
• 1200-2400 - good place to be
• 2400-3200 - mileage starts to decline
• 3200-4150 - owch
• 4150-4500 - do not go there

These are specific to the 1.5L, NHW11 model Prius.

Bob Wilson

[dcb]

Originally Posted by bwilson4web

...
The Brake Specific Fuel Consumption measures how much power is provided versus fuel consumption of an engine in a test stand with the throttle wide open

Let me chime in here, I think they have to be using several throttle settings in order to create the "isobars" on the good bsfc maps, otherwise the load would be fixed at 100% for any given RPM and there would not be any data for consumption at less than 100% load.

[bwilson4web]

I don't know how the islands, the areas, of specific fuel consumption are plotted but it makes sense there is some throttle operation. In my case, plotting BSFC along the operating line provides a useful guide. Here is one of the better articles about BSFC:

Brake Specific Fuel Consumption

As Julian Edgar points out in the article, partial throttle operation significantly reduces engine efficiency. So it makes sense partial throttle operation is used to map the inefficient parts of the chart.

Bob Wilson

[some_other_dave]

You can think of these plots as 3-D plots. You have load (or torque, both of which are to a great extent determined by throttle position) on the vertical axis, RPM on the horizontal axis, and fuel consumption on the axis that comes out of the screen. The plot is like a contour map of those three things.

-soD

[cfg83]

some_other_dave -

Originally Posted by some_other_dave

You can think of these plots as 3-D plots. You have load (or torque, both of which are to a great extent determined by throttle position) on the vertical axis, RPM on the horizontal axis, and fuel consumption on the axis that comes out of the screen. The plot is like a contour map of those three things.

-soD

That's what I thought. In dcb's plot we speculated that WOT was the continous line at the top connected by the black dots :



CarloSW2