> For all this talk about lean burn, it doesn't seem like anyone has actually
> mentioned what it is. My understanding is that it is the special valve mode that
> was originally developed for the 1992 Civic VX. In that year, the Civic engine
> came with four different valve schemes:
CX <snip>
DX <snip>
VX <snip>
Don't forget EX or Si. Same valve train as the DX with a different lift/duration cam and maybe valve size(s). And a transmission to match.
><snip> Since valves are a limiting factor on an engine defining redline, <break>
Valve lift and duration will be the primary limiting factor in the attainable RPM of the mechanical capabilities of an engine. Unless you force feed it e.g. supercharger or turbocharger. The ultimate limiting factor is the liner velocity of the pistons/rings. At some point the pistons/rings simply due to the heat of combustion and friction will begin to weld themselves to the cylinder wall. As you approach this point durability becomes unsatisfactory.
> these high performance versions redlined closer to 12,000 rpm while the other
> versions redlined around 6,000 rpm. They got more horsepower and less gas
> mileage than the DX and the transmission was geared lower so the engine
> revved higher at any given vehicle speed.
What I remember of this bygone era was that no production version of any Honda had a redline above 9000.
Honda's evolution of the "lean burn" actually started way back in the late 70's I believe with their CVCC engines (Compound Vortex Combustion Chamber). Those engines were equipped with 3 valves per cylinder, 2 conventional and a 3rd CVCC valve. Initial combustion took place in a pre chamber then the CVCC valve opened the burning mixture into the leaner main chamber. It also required a 3 barrel carburetor with separate intake runners for the CVCC system. And ultimately enough vacuum lines to make you crazy when trying to isolate a vacuum leak.
This was done primarily as an emissions control design and allowed Honda to delay installing an exhaust system catalyst.
The VX model was (as I remember) Honda's first production model of their VTEC system (Variable valve Timing and lift Electronic Control)
http://www.leecao.com/honda/vtec/index.html
<snip>
> So, I think the "lean burn" mode is the mode where half the valves stay closed
> while the others do all the work. I witness it as a point when the gas mileage
> progress bar suddenly boosts about 20% and there's a very subtle sense of lessened
> horsepower. It takes a fine sense of touch on the accellerator to feel where this
> kicks in and out, and as others have said, on level ground, it is easier to do at
> lower speeds than at higher speeds.