Success story. Kinda... Average speed 77 mph

[turbovr41991]

This is a success story, kinda… People from team Honda might want to boot me from the team challenge after reading it though. Lol. I view it as a success, but it is also just about the worst tank of gas I have had since I owned the car. This past weekend, I took the family for a trip to Chicago. The wife said we could take my Civic to Chicago on one condition; that I go the speed limit (mostly 70 mph...) Seeing how it was either the civic, or a larger 4 door full size car that would get 23-27 mpg, opted for the civic at 70 mph.

I could not get lower RPM lean burn. It hit a patch of traffic early on, and could not get it to go back in. So not having the option screwed me right away. I tried many different techniques, but could not get any good gas mileage numbers while going 70 mph. It was just too fast to be in the efficient range of my 4th gear lean burn at 2500 rpm. It was also higher RPM’s, engine load and throttle than I would have liked to see under normal driving in 5th gear. So, with no other viable option, I decided to test out a max load/TPS lean burn in 5th gear over 400 + miles.

Speeds stayed between 73 and 80 mph with the average around 77mph. Engine load was always 88-91 and throttle position sensor was pegged at 30 (sometimes 32-33 at higher RPMs). Still a good test and the wife was happy. End result was 43.74 mpg over those 400 miles averaging 77 mph.

[Saskwatchian]

Forgive my ignorance but are you saying that it was more efficient at 77mph than at 70? also why would anyone cruise in 4th at 70mph? It makes me wonder if the car is geared too high for how it is driven?

[turbovr41991]

Originally Posted by Saskwatchian

Forgive my ignorance but are you saying that it was more efficient at 77mph than at 70?

The short answer is under its current conditions and limitations, it was more efficient at 73-75 mph than at 70 mph.

This is because my car was requiring 2400-2500 to enter lean burn mode which nets about an extra 10 mpg at highway speeds. So ultimately:

1) Going 70 mph at 2300 RPM in 5th gear in normal burn nets about 36 mpg.
2) Going 73 mpg at 2400 RPM in 5th gear in lean burn nets 45 mpg.

If I was able to get into lean burn at lower RPMs (as I sometimes am able to do.) I would have expected to see better results at the slower speed, but since lean burn was only engaging over 2400 rpm, it made the higher speed with lean burn more efficent than the lower speed without.

Originally Posted by Saskwatchian

also why would anyone cruise in 4th at 70mph? It makes me wonder if the car is geared too high for how it is driven?

Driving on flat I can be at 2400–2500 rpm going 67-63 mph in 4th gear in lean burn netting 54-58 mpg on flat. It also is ideal for climbing most hills at highway speeds getting 40-50 mpg depending on the incline.
The VX trans is geared really high, but I am finding a use for all the gears. It combined with lean burn gives me more options. And with more options I have a better chance of using the optimal combination to use the least amount of fuel as possible.

[brucepick]

Originally Posted by turbovr41991

... Still a good test and the wife was happy. End result was 43.74 mpg over those 400 miles averaging 77 mph.

Nice job. Not too many can get 43.74 mpg at 77 mph AND keep the wife happy!

[Saskwatchian]

@ Turbo

That is really cool, I didn't know lean burn needed the higher revs, makes prefect sense. Thanks for the explanation.

[turbovr41991]

I think it is more the finicky ECU and EPA restrictions that do not allow the lower RPM lean burn all the time. The procurer to the HX, the civic VX is able to lean burn at lower RPM’s. I have been told the NOx levels were too high and to get lower level of NOx, the low rpm lean burn was taken away.

[mcrews]

almost makes me want to buy a civic........

[mcrews]

Almost makes me want to buy a civic....!

[turbovr41991]

Yesterday I was running late to work and rocked the high speed lean burn. Sad watching my 60 mpg I was getting drop to 54, but still a nice option to have a semi efficient high speed option. I just try not to make a habit of it too much as it really kills my average.

[gasstingy]

Two thumbs up for mid-40's mpg @ 77 mph! My Rio's mileage drops like a rock as I speed up. Most of my semi-rural driving is @ 50 mph unless someone is close behind me and the speed limit is 55.

Congrats for keeping the wife happy on a 400 mile road trip. My wife refuses to even discuss going to Dallas {>700 miles one way for me} in the Spring in my Rio. We'll be sucking gas in our Silverado pickup. The bright side is it's a comfortable vehicle and rides great. It's also cheaper than renting a fuel efficient car that she would agree to do a road trip in.