4th gear for maximum efficency?

[thoraldshib]

I just watched "Robot Catina's" youtube video on fuel economy testing "S4 E43. 2000 Honda Insight" where he tells about his research using the Insight and that it achieved best fuel economy without IMA working, and while top speeding in 4th gear. I have a gutless Lean Burn 1999 Honda Civic D15Z7 with long gear ratio transmission (dyno proven 86 HP to wheels) I have never exceeded 42 MPG despite expectations of 48-50 , I'm thinking of trying driving it without using 5th gear, car is so gutless I normally drive it up to 50 MPH in 1st gear then plop it into 5th gear. Has anyone else tried this? I always thought 5th gear would be the best on economy

[Gasoline Fumes]

I just watched the video too. And I also have a 2000 Insight. I average 64 MPG using 5th gear as much as I can. I suspect Jimbo might have a clogged fuel filter.

50 MPH in 1st gear probably explains why you only get 42 MPG. If that is really necessary, something might be wrong with the car.

[Ecky]

I've owned 3 Insights and all make better economy in 5th. I've found the best economy comes from short shifting - keeping it under 2000rpm or so when getting up to speed, and when cruising, keeping it in the highest gear where it's still above idle RPM. At least in these engines, RPM is the enemy of all fuel economy. Rev it up, and kiss the gas mileage goodbye.

[Andyman]

I like to watch Robot Cantina videos too. I had a 1994 Honda Civic that got poor fuel economy, usually about 35 MPG. I realized that it ran rich because of the smell. I made three changes: tighten the timing belt tensioner, advance the ignition timing a few degrees and connect a resistor to the MAP sensor to tell the ECU that it had a lower manifold air pressure. I tried different resistors to get the right fuel mixture. After that I was able to get up to 50 MPG on the highway. I believe the engine was running rich because the old timing belt retarded the valve timing and reduced air flow into the engine.

If your engine has less torque than normal, it could be caused by a restricted air filter, a clogged exhaust system, late valve timing, late ignition timing, lean fuel mixture, high altitude, or low compression pressure. If something knocks too much such as a rod bearing or a loose timing chain, the knock sensor might detect it and cause the ECU to retard the ignition timing. If the check engine light is on, be sure to scan for trouble codes.

I think I remember that the Insight in the Robot Cantina video got better fuel economy in fourth gear because it wouldn't use lean burn in fifth gear. That might be because this engine was also low on torque. My best guess is that the valve timing was retarded because of a worn timing belt or chain. If the engine uses a distributor, the ignition timing is also retarded when the valve timing is retarded until the distributor is adjusted.