[t vago]

I think this "10%" improvement is kind of misleading, given that MetroMPG started off with a FE of 71.2 MPG (or 3.3 L/100km).

I ran the numbers, and found that he saw a reduction in fuel consumption of 0.3 L/100km. Given his starting consumption of 3.3 L/100km, that is indeed a 10% improvement.

However, if I were to apply this same fuel consumption decrease to my own FE (last tankful was 20.5 MPG or 11.5 L/100km), I would find that I would only see a 3% improvement in fuel consumption.

Alternators do not take that much energy to spin. Noticeable, yes. However, will somebody currently seeing 25-30 MPG see a 10% improvement if they disconnected their alternator? Nope.

It's not to say that one should not look at improving the efficiency of the alternator (or removing it in favor of some other form of battery charging). For instance, if I again use my truck's performance as an example, I would find that I would pay roughly $2.65 per fillup for using my alternator. I would love to cut that figure down.

I'm only saying that one should not expect vast improvements from alternator modifications/deletions. Probably not a really good idea to utilize percentages when talking about FE improvements, either (at least if one is considering modifications that do not change the dimensionless coefficient C(d) ) . Heck, for that matter, it'd probably be better to talk about FE in terms of L/100km rather than MPG.