Fuelly Forums - 2006 mods vs. technique

Driving technique won over mods by a pretty wide margin: 37.5% vs. 28.0%. Though you'll have to buy into my "comparison" method to believe it. It's pretty inexact (to say the least...)

Tallying just the mods ...

5.2% tranny swap
https://www.metrompg.com/posts/tranny-swap.htm

10.3% alternator optional
https://www.metrompg.com/posts/alternator-optional.htm

2.3% kardboard kammback
https://www.metrompg.com/posts/boat-tail-prototype.htm

2.3% mirrors
https://www.metrompg.com/posts/mirrors.htm

5.7% grille block & rear wheel skirts
https://www.metrompg.com/posts/grille...ing-part-2.htm

2.2% undertray

= 28% total theoretical improvement over base from measured mechanical/aero mods

I'll be the first to admit this tally is flawed on several levels: 1) the weather conditions weren't the same for all tests; 2) the speed wasn't exactly the same for all tests (but close to 55 mph); 3) the effects of individually tested aero mods can't simply be summed because their effects interact with one another ... the car is probably more or less than 28% better with all the mods in place. But the car was never driven with all of them in place at one time and then without.

Driving technique ...

To do this comparison, I looked at 3 tanks in Firefly #1 which were predominantly city driving. When I was using that car, I wasn't employing coasting of any form, or P&G/codfishing, and there were none of the mods listed above.

Firefly #1, 3-tank tally: 1474 km, 83% city driving ... 5.2 L/100 km / 54.0 mpg (Imp) / 45.0 mpg (US)

Blackfly, 3-tank tally: 1724 km, 83% city driving ... 3.3L/100 km / 86.5 mpg (Imp) / 72.0 mpg (US)

If you do the math, that actually works out to a 60.2% improvement for the Blackfly.

The biggest flaws in this comparison are: 1) it assumes the "base" cars are identical (which they were on paper, but probably weren't in reality) ; 2) the Blackfly has some mechanical & aero mods on it that the other car
didn't have. Based on the values in the mods list though, we can correct for these mods:

- 5.2% transmission advantage
- 10.3% alternator advantage
- 1.2% aeromods advantage (calculated based on avg. city speed of 25 mph vs 55 mph for the tests)
- 6.0% rolling resistance (this is a WAG - the Blackfly has LRR tires and higher pressures than the first Firefly had)

------
-22.7% total deductions (this is actually a liberal estimate, because the Blackfly was not running alternator-less, nor with all aero mods, and the taller tranny was only in place for 2 of the 3 tanks)

= 37.5% estimated difference due to driving technique