BSFC

Hi,

I just watched the Tuning Fundamentals video on BSFC. While I understand the concept of BSFC and the fact that a higher BSFC indicates a less efficient engine, the video states that BSFC is a measure of the amount of fuel energy wasted, i.e. an engine with a BSFC of 0.7 wastes 70% of the fuel energy. I am curious to see the maths behind this. Can you guys provide this?

BSFC is a value in lbs/(hp.h)

(at least for a value of "0.x". It can also be expressed in g/(kw.h) in the metric world).

A BSFC of 0.7 means you use 0.7lbs/h for each Hp you produce, not a waste of 70%.

As for the math behind it, it just a ratio between your specific* fuel consumption and your power.

(*: at a given RPM / load)

Now if you want to translate the BSFC to efficiency, you have to know the "potential" of the fuel being used.

A BSFC of 0.7lbs/(hp.h) with regular gasoline, that give you an efficiency of ~19% (so 81% lost)

To give you a perspective, most engine this days have an average efficiency around 25% (BSFC of 0.52lbs/(hp.h))

We're actually in the middle of a rewrite of the EFI Fundamentals course - This was our very first course and there are a few areas we wanted to change to make the course better, more interesting and more relevant. The point of the discussion on BSFC was aimed at showing that a higher BSFC represents an engine where a high portion of the fuel is being wasted - Perhaps however not as a specific value.

Thanks Andre. Ludo, no need to explain what BSFC. I understand the concept. My question was related to a specific statement in the video, i.e. that 0.7 bsfc means 70% of the fuel is wasted.