Today's fuel efficiency test explored the efficiency of the Fit's engine in different gears at a constant speed.

Each test was done on a 1 mile stretch, almost perfectly flat, with a few twists in the road. No lights, no climate control, no precipitation, engine fully warmed up, ambient temp 43F/6C.
Similar to my previous tests, I go up the road with the cruise set, note the AVG mpg at the end of the test stretch, turn around, and start over, repeating until I had the data I wanted.

Test 1.1: 35 MPH, 6th, 1670 RPM, 44.1 MPG
Test 1.2: 35 MPH, 6th, 1670 RPM, 45.7 MPG
Test 2.1: 35 MPH, 5th, 1860 RPM, 42.5 MPG
Test 2.2: 35 MPH, 5th, 1860 RPM, 44.6 MPG
Test 3.1: 35 MPH, 4th, 2170 RPM, 44.9 MPG
Test 3.2: 35 MPH, 4th, 2170 RPM, 47.8 MPG

Test 4.1: 35 MPH, 6th, 1670 RPM, 44.2 MPG
Test 4.2: 35 MPH, 6th, 1670 RPM, 45.7 MPG
Test 5.1: 35 MPH, 5th, 1860 RPM, 42.3 MPG
Test 5.2: 35 MPH, 5th, 1860 RPM, 44.4 MPG
Test 6.1: 35 MPH. 4th, 2170 RPM, 44.6 MPG
Test 6.2: 35 MPH, 4th, 2170 RPM, 46.9 MPG

Test 7.1: 30 MPH, 6th, 1430 RPM, 45.1 MPG
Test 7.2: 30 MPH, 6th, 1430 RPM, 46.7 MPG
Test 7.3: 30 MPH, 6th, 1430 RPM, 44.9 MPG
Test 7.4: 30 MPH, 6th, 1430 RPM, 47.4 MPG
Test 8.1: 30 MPH, 4th, 1860 RPM, 41.6 MPG
Test 8.2: 30 MPH, 4th, 1860 RPM, 44.3 MPG
Test 9.1: 30 MPH, 3rd, 2430 RPM, 44.7 MPG
Test 9.2, 30 MPH, 3rd, 2430 RPM, 47.2 MPG

I predicted that 6th gear would always yield the best results, and that 5th would be slightly worse, and 4th would be worse still. I was wrong.

The worst test was the 30 MPH test in 4th gear at 1900 rpm, and the next worst was the 35 MPH test in 5th gear also at 1900 RPM. Judging by the previous test I conducted (linked below), it appears that this engine does not like being revved at just under 2000 RPM. I'm not sure if it's all Fit 1.5L engines or just a quirk of mine. 1800-2000 RPM seems to be a major weak point of the engine in terms of efficiency. On the other hand, it seems that the 2400-2500 zone is extremely efficient. The 30 MPH tests between 6th and 3rd were nearly identical despite the 1000 RPM difference. It's shocking to me that the Fit doesn't care whether you drive 30 MPH in 3rd or in 6th, but punishes you if you take 4th at that speed. I was also shocked that 4th gear would outperform 6th gear at 35 MPH in terms of efficiency, but somehow 5th was worse than either.

If my Scangauge is to be trusted, I should avoid the 1800-2000 RPM zone of the tachometer if possible. I need to do more tests to investigate this discovery. I thought I knew the best shift points for my car but apparently not. More testing with longer duration and higher speeds are on the way as I have free time. I really need to wait until the roads improve, because my car is absolutely filthy after putting almost 30 miles on it in breakup weather.


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Whoaw that's pretty cool, thanks for crunching the numbers. Maybe that dip is due to VTEC profiles, might be a spot of inefficency in the transition between cam profiles. I saw your other post and I think that it was mentioned that load also affects fuel efficiency, so it'll be interesting to see how all the data adds up. Hope you're having fun !

 

I was also thinking the dip in efficiency was due to i-VTEC cam profiling, but I wouldn't know how to test it.

I'm having a blast. It's nice to know I can drive my car in any gear I want almost without penalty to fuel economy as long I avoid this known weak spot in the rev range. I used to complain about the strange gearing but it makes more sense once you figure out that the mid 2000s of the rev range is where you want to be, then instead of wishing for a taller 6th by 42 mph, 6th is useless until 47 mph. Actually, 6th is great when you're going about 22-35 mph downhill, but you get I mean.

 

A steady state test at a highway cruising speed would make more sense because at 30-35 mph, you are typically in city stop and go traffic situation. It seems like the more numbers you crunch the more confusing they look. Yea, your science project conclusion did not support your hypothesis. That would definitely give me sleepless nights. For me, getting over 40 mpg at 62-63 mph is good enough. With a good tailwind, I have gone over 500 miles before having to fill up. You may not know it, If you top the tank off, you can fill a little more than 11.3 gallons of gas. I like playing that game.

 

These tests were done on a 1 mile stretch 35 MPH road with next to no traffic and no stops. This road has really good turnaround points, and I like that I won't aggravate traffic or get aggravated by traffic. I tested 30 and 35 MPH because those are the speeds that are the most common on my commute. I've gotten well over 400 miles on multiple tanks with over a gallon to spare; just check my Fuelly, and I'm really happy with those numbers.

The main reason I wanted to do these tests was to confirm if my predisposition to choose 6th gear whenever not accelerating was the right choice, and to see which speeds would give me the best MPG. I haven't lost much sleep, but it fascinates me how wrong I was, meanwhile today I got 2 personal bests for AVG MPG on my commute to and from work. The warmer weather is helping, but knowing to stay out of the "awkward zone" of the rev range really helps too. Pretty nice to know that I can avoid semi-lugging my engine and not only avoid a penalty to MPG, but in some cases get better MPG. I'm 100% happier for having done these tests so far, and I look forward to doing more.

 

I've got a CVT, but I think my recent experience with my "new to me" 2018 sport may go toward supporting your findings. With all the talk about carbon buildup, oil dilution, fouled injectors, etc, I decided at least once a week, I should run the fit a bit harder, a la "Italian Tune Up" style. Since I consistently get in the low to mid 40's MPG on my commute, I expected the "frisky" commute to reflect lower MPG. I was wrong. Keeping the CVT in sport mode for a good 4k RPM at 75 MPH cruise, and going manual with the paddles several times to get the RPM even higher for onramps, etc, the Fit still reported low to mid 40's on my same commute. I've done this several times now, and the results are always the same. The only thing that I've seen lower my MPG is stop and go rush hour style traffic.

All that to day, my results seem to agree with yours, that the Fit's GDI 1.5 is quite efficient even at higher RPM.

I'm at no risk of being accused of proper scientific testing here, but it's enough to take notice.

 

Those are some awesome observations you made. Thanks for letting me know that the CVT doesn't seem to hurt fuel economy by driving at higher revs either. I'd love to get my hands on a CVT model to do some testing.

Without fuel directly flowing past the intake valves, an Italian Tune-up style of driving won't do an awful lot to clean up any carbon that has already built up, but driving at higher rpm might slow down any carbon buildup that has already started. As far as oil dilution, I think that's just from the heating and cooling cycles of the engine. Since I drive in a cold climate and make frequent short trips, my oil gets changed every 3000 miles or 6 months, period. I have nothing to say about fuel injectors other than possibly the quality of fuel might play a factor or it could just be the Fit has a design flaw with its injectors. The L15B1 was the first 1.5L Honda engine to get direct injection, so maybe OEM made a poor judgement between economy and durability, but I have no idea.