[mpg_numbers_guy]

Originally Posted by Ecky

Well perhaps I should put it this way: Neither alone will give the full benefits, but either would be of benefit.

I would think replacing a transmission with one that has taller gears would be easier than taking a transmission out, disassembling it, rebuilding it with a custom gearset, and reinstalling it.

I believe the ECU in your car needs to match the transmission type though, which is to say, you could not pair a manual transmission HX computer with an LX automatic transmission.

Oil Pan 4 probably points out the cheapest best solution though - replace the computer with a custom one. Modders do this all the time, so they're relatively inexpensive and well understood. By replacing your factory ECU with an aftermarket one (e.g. Hondata) you can then take it to a tuner, who can program lean burn and perhaps different (better) shifting behavior into your existing engine and transmission. A custom computer would also allow for an automatic transmission with an HX engine, if you so desired.

So I take it that the increased MPG of the 7th gen HCHs is less due to the electric assist and more due to the lean burn and taller gearing?

True, but both sound like one heck of a challenge lol.

Are you saying I can have the ECU computer reprogrammed for lean burn and to somehow make the manual tranny work as an automatic?

Originally Posted by oil pan 4

Just going to lean burn and changing nothing else can get you a 10% to 20% boost in fuel economy.
If all you do is swap in the lean burn engine and ECU all you should expect is no more that 20%.

A significantly greater than 10% improvement for just one mod. wistfull look