[RobertISaar]

Originally Posted by MetroMPG

I'm curious to know more about this 'highway fuel mode'. (Which cars, how far from stoich / 14.7:1 ?)

it isn't enabled in a factory calibration, but the code exists to do so and requires setting only a single option to enable it. the code currently exists to allow up to a 25.5:1 AFR, though it could be modified to a higher range if needed. factory calibrations actually have the target AFR set to 15.4:1, but since it won't enter it due to the option not being set, it never happens. set the option, and when in low load(adjustable, though i usually have it disabled when hitting ~80kPa or higher) and at a high enough speed(also adjustable, i like the ~50MPH range to enter, drops out under 45), the PCM goes into open loop fueling and ignores the O2 sensor until highway fuel mode is exited, upon which closed loop fueling resumes. even after very extended periods in highway fuel, the O2 sensor seems to come alive pretty much instantly(starts switching), so no delay when going from lean cruise to closed loop has been necessary for me. i tend to run a 16.2:1 AFR since it's about as lean as i can go before i feel it's too close to a lean misfire.

Originally Posted by MetroMPG

The lean burn you see talked about typically here is the Honda stuff, where ratios go quite far away from stoichiometric - e.g. the 1st generation Insight goes as far as 23 to 1 aided by swirl in the cylinder induced by leaving one intake valve closed under light load. (Not sure on the ratios available in the Civic HX & VX models). When lean burn kicks in on the Insight, MPG goes up ~25 mpg.

i know with my engine, there is no possible way for me to get anywhere near that kind of ratio, once above ~17:1, it will lean misfire consistently. i guess when the engine is built to do so, some wonderful efficiency benefits can be realized.

Originally Posted by MetroMPG

FYI, that only works if you can also control RPM (manual transmission) to keep engine speed relatively low while under relatively high load. (It also only works if you NEVER have to brake or otherwise slow down soon after a high load/low RPM acceleration event, otherwise you just tossed more fuel out the tailpipe than a slower acceleration event would have burned.)

i can do this to some degree.... i've messed with TCC lockup points considerably since the factory settings were made more for smoothness than efficiency, now the TCC will lock as low as 28MPH in 3rd gear and will stay locked through the shift to 4th gear at as low as 43MPH. i may have to impliment the ability to lock the TCC in 2nd gear normally(which the PCM will do anyways if it detects the transmission as overheating) as well, since i may see a benefit there. the factory torque converter is rather loose with a ~2100RPM stall speed, so giving any significant amount of throttle will cause the engine to shoot up to at least that speed. BTW, the factory settings didn't allow the TCC to lock until ~45MPH regardless of gear... with that converter, you could feel the engine just rev but not actually move the car. kind of ridiculous.

i can see why it's not always the answer to briskly accelerate, especially with short and potentially short distances before needing to slow down, it's certainly something you learn to anticipate driving around here.

Originally Posted by MetroMPG

I always start by recommending instant MPG instrumentation. Your car's entry says "custom" there. Vac gauge? Anything else? Ideally you want a resettable MPG gauge so you can start playing the game. (High score on typically repeated routes, and also potentially for testing mods.)

currently, using my laptop while logging to monitor the engine for an instantaneous display. i cannot seem to get an an accurate average fuel economy calculation to work with it though, but the software i'm using to log(tunerpro RT) was never intended to be used for that anyways. depending on how long i plan on keeping the car around, i may use the trip computer from a 94-95 grand prix or a 88-93 cutlass supreme for use as a instant/average MPG estimation. i love the cutlass units due to the blue/green vacuum florescent display.

Originally Posted by MetroMPG

Aside from that, given where you live (Michigan), and the time of year we're sliding towards, I'd start looking into mods that address winter conditions like a partial grille block (also helps reduce aero drag); block heater. If you spend most of your time above 40 mph, focus on the aero mods for sure.

grill blocks and aero mods in general are certainly something i've given a lot of thought to, and in the winter, i could probably get away with blocking the entire air dam area and having the little "grille" slots provide enough cooling.

http://www.theautochannel.com/media/...e_carlo_ls.jpg

not the greatest picture, but it should show enough to get a decent idea. if i had the money to do so, i would likely look into something to actuate a grill block to full open and full closed based on coolant temps, similar to how certain new cars are doing so, and then it could be left on year-round without worry.

i live in nearly the middle of nowhere(on the edge of a population ~500 village), so my trips are about ~5% speeding up and slowing down from 55MPH, ~5% traveling at in-town speeds, and 90% just maintaining that 55MPH speed throughout the hills around here.