What's better, lean burn or tall gearing?

[California98Civic]

Which is better? It depends on how your car is engineered and how you are going to drive it, but I thought this screenshot I just bumped into in my notes might be a useful. It is a reminder about how the original VX was designed. I assume that they are using some approximation of the EPA test cycle for these estimates. Notice that gearing is credited with 21% of the FE gain of the 1992 VX over the 1991 DX at the time, while lean burn is credited with just 5-10%. In fact, all the vtec-e stuff amounts to less impact on FE than gearing.

[Gasoline Fumes]

I'm borrowing a 2001 Insight and lean burn seems to double the instantaneous cruising MPG. Maybe the test cycle doesn't let Hondas enter lean burn much? The best tank in the Wagon with the original trans (shorter FD than '91 DX hatchback) was 70 MPG. Best tank after installing the CRX HF trans (taller than '92 VX) was 82. So the gearing increase more or less matches what I saw.

[California98Civic]

Originally Posted by Gasoline Fumes

... Maybe the test cycle doesn't let Hondas enter lean burn much?...

I bet that's right. Certainly an ecomodder worth his salt can get mch more out of thre car's engineering. But that's also true of skilled driving with taller gearing. The Insight prolly has more advanced LB parameters than the VX. I know the 6th gen HX Civic did. And the first Insight, of course, came after the HX.

[oil pan 4]

Lean burn was good for another +20% for me.
I would expect up to +20% from a fairly radical gear change from 4.11 to 3.21, what I have in store for the suburban or from 3.73 to 3:1 or 3.25 to 1 for the firebird.

[ChazInMT]

I just replaced my 2004 Civic EX manual transmission with an LX letting my 75mph RPM drop to 3050 from 3800. I drove from FL to OH but did not see great gains in efficiency. I will be driving to Arizona then back to Tennessee in the next 6 weeks so I should have a better idea. I did remove an upper grill block that I didn't replace when I changed the gearbox out, and didn't put it back in. I also did not drive as well as I could have. It does make highway speeds much quieter not going as far up in the RPM range, a nice bonus.

[California98Civic]

Originally Posted by ChazInMT

I just replaced my 2004 Civic EX manual transmission with an LX letting my 75mph RPM drop to 3050 from 3800. I drove from FL to OH but did not see great gains in efficiency. I will be driving to Arizona then back to Tennessee in the next 6 weeks so I should have a better idea. I did remove an upper grill block that I didn't replace when I changed the gearbox out, and didn't put it back in. I also did not drive as well as I could have. It does make highway speeds much quieter not going as far up in the RPM range, a nice bonus.

Well, I'd say if you delted two things that are well-known to give you better FE (grill block and hypermiling) and still go the same FE as before the swap, then that suggests the swap might have saved you.

[MeteorGray]

I've always liked gearing that allows low RPMs while cruising on the road. No only is it generally good for economy through less piston speed and related friction, but it's more relaxing for the driver not having to listen to a screaming engine for hours on end. I also believe it's good for engine longevity due to less wear and tear provided, of course, the engine is not being lugged.

My 2015 2.0L Mazda3 with the six-speed automatic is an example of my preference. At 60 mph, it's turning over at a leisurely, diesel-like 1700 RPM, and at 70 mph it's just reaching 2000, all the while developing about 85% of its maximum torque. I do like those long legs.

I believe this is part of the reason I've been able to record an overall 43.4 mpg during the 23,000 miles I've driven it so far. I don't hypermile per se, but I have driven it almost exclusively on the highway with essentially no short-trips in between. Another help is the 13.0:1 compression ratio, which Mazda has managed to employ while allowing the use of cheap ole RUG. My overall fuel cost is at 4.5 cents per mile so far, not bad for a car I got out the door for $20K brand new.

My data does not answer the OP's question about lean burn, but it does support the use of tall gearing, for sure.