Possible mistake?

Earlier in the presentation, sir had mentioned that BSFC equation is fuel flow (Lb/Hr) ÷ HP. Later on he mentions that NA+Carbourated engines have a BSFC between .48 and .55 LB/HP/HR. I'm wondering if that was a format mistake or if the equation changed and I just didnt catch it. I'm a noob tuner so it kinda threw me off.

The easiest way to remember it is how much fuel (in pounds) an engine needs to produce 1 hp for 1 hour. NA engines indeed have better BSFC because they don't produce that much power per cylinder comparing to turbo or supercharged engines what requires additional fuel to be injected in combustion chamber for mild cooling effect (that is what makes their BSFC higher).

More accurately, forced induction engines apply parasic losses on the raw engine output - a direct mechanical one with superchargers, excess exhaust pressure with turbo's. those parasitic losses require engine power, and hence additional fueling, to overcome.

If we take a look at torque vs AFR graph we'll find out that maximum torque is achieved around 12.6-12.3 AFR for pump gas with 93 (USA) octane rating. No additional fuel will get any extra torque thus no extra power. Ideally all forced induction engines should be working with that AFR to produce maximum torque and power but they just can't simply because combustion chamber temperature gets too hot and pump gas starts to knock that forces you to retard ignition timing resulting in making less power than can be had otherwise. In order to bring combustion chamber temperature down and have a couple of additional ignition timing degrees to make a bit more power some additional fuel is injected as it absorbs some energy when is transitioned from liquid to gas (latent heat of vaporization is not as good as of alcohol fuels or water but still good enough to have mild cooling effect). So additional fuel isn't consumed to provide more power to rotate any additional hardware or fight any other losses (the graph clearly shows us that richer air-fuel mixture doesn't provide more torque) but simply to bring combustion chamber temperature down.

I've learnt it from Greg Banish - ex Ford OEM calibrator (Andre once had an interview with him).

Here is very good topic explaining BSFC

https://x-engineer.org/brake-specific-fuel-consumption-bsfc/

Combustion chamber cooling by fuel is also mentioned here about Ecoboost engine.

https://x-engineer.org/air-fuel-ratio/

Air efficiency on the other hand usually goes up with boost, to a point anyway, as parasitic losses represent a smaller portion of total output.

In theory, with stable combustion BSFC can be lowered on boost if water injection is used.

I remember David Vizard talking about getting significantly more power from NA engine with 16:1 compression ratio by simply employing water injection.