For some reason, it seems to be "common sense" on this forum that running leaner will save fuel. I have never heard any substantiated proof of this. Could someone please point me to an article somewhere?
The reason I'm so skeptical is because when you run lean, your engine also runs less efficiently. So even though you are lean, in order for the engine to create enough power to keep moving you have to step on the throttle further. On my car (which is 100% tunable on-the-fly with a laptop from the driver's seat), when I try to get leaner than 14.7:1, I might not get pinging right away, but I can feel the engine start to stumble and miss.
Also, if you run lean, you speed up your combustion so instead of a smooth pressure increase you get all the power in a quick "boom" which tends to hammer the heck out of the bearings.
'Leaner' is a vague term. If you're going to try running leaner, it helps to know how lean. Here's a good chart: www.gassavers.org/showpost.php?p=92069 I've seen similar charts in other places. Also be aware that most of the stuff you hear about a motor that runs 'lean' is from running WOT and aiming for max HP where 'lean' might mean a 13.0:1 A/F ratio, 'just right' might be 12.0:1, and 'rich' might be 10.0:1. This thread is about running at the other end of the spectrum where combustion takes on different characteristics.
When I first started using lean burn code in my car it only had one preset A/F ratio (16.1:1). I could feel the power drop off at mid throttle, while at light throttle it felt fine. If I richened the A/F ratio a little(15.8:1), the power at mid throttle felt nicer, but then it was too rich to save much gas at light throttle. That's why I rewrote the section in my ecu that sets the A/F ratio. Now the ecu also looks at the load/airvolume to determine the A/F ratio. At the lightest loads it goes slightly leaner than 18.0:1. As airflow/power requirements go up, the A/F ratio gradually gets richer.
Yes, the throttle has to open a little more when running lean. This increases efficiency by reducing pumping losses. On modern fuel injected cars, this also increases the load seen by the ecu, which reduces ignition timing and makes the power feel soft, decreasing efficiency. That's why I've added a degree or two in the light load/ cruise portions of my timing map; it makes up for the timing loss from running at higher perceived load.
From what I've read, flamefront propogation slows down with A/F ratios leaner than around 16.0:1 because the fuel molecules are farther away from each other. This is another reason to bump timing.
Would you care to enlighten me as to what you have done? I looked at your gas logs. Very impressive. Your car should only be at 26mpg.
That's a big question. Aside from the mechanical mods listed in my profile and driving techniques, there are many ecu mods. I'm lucky to have access to a commented disassembly of the factory ecu in my car, otherwise I wouldn't have found as many sections to change. The ecu mods are focused on reducing fuel usage at all times, such as:
leaned out startup enrichment
shortened the ammount of time that startup enrichment is active
leaned out cold ect enrichment
lowered idle at all engine temps (idles low when cold)
lowered rolling fuel cutoff threshold at all temps
lowered temp threshold where ecu switches from cold enrichment to warm enrichment
leaned out various O2 sensor switchpoints and targets
tweaked the timing and fuel maps so I can lug the motor with less harsh vibration
load based knock sensor management to control how much timing is pulled when the engine knocks, how long the timing is pulled, and when to ignore knock
added lean burn code with triggers for vehicle speed, throttle position, and airflow
adjustments to the EGR map
changed the code to match the bigger fuel injectors and upgraded MAF so they work like stock parts.
There may be more that I'm forgetting, but those are the major changes that made a difference.
I'm sure much more knowledgible people will post after me, but my understanding of the VX VTEC-E engine is that it alters the intake valve timing specifically to promote swirl when in lean-burn mode. My gut tells me you'd need to do that in order to prevent a lean-missfire condition with your D15B.
The VTEC-E is just a VTEC. Works the same as any other VTEC. The difference is that the pistons are dished and the head's combustion chamber is small. Also the ECU has an alternate FUEL /Timing map for LEAN Burn Mode.
If you have a honda -> www.moates.net, http://forum.pgmfi.org/ and any other honda tuner board. Basically you just CHIP your ECU and write the new code to your chip. CROME is popular tuning software for Honda's. You'll also need a Wide Band O2 to tune it right.
I have a chipped ecu. I got a chip burner from moates.net
I don't have an egt gage. I had one for a while but it really didn't tell me much since it's affected by other variables. I have a knock gage and wideband O2 sensor in the dash, plus I'll use a datalogger when I'm changing the tune.
Um, the Honda VX and HF? I think this is proof that lean AFR's work.
Sorry but since I don't know the Honda engine design, that means nothing to me. What about a Honda engine makes it suitable to run lean, whereas most other engines strive to run at the theoretical optimum of 14.7? rod/stroke ratio? Compression ratio? Cam design? Retarded spark timing? Perhaps you know of a website that explains what makes the Honda design so different.
I'm also assuming that the AFR being discussed is not during deceleration or something, this is during steady-state cruising.
According to the "lean burn code" as described above, in order to run more economically somehow the injector PW must be decreased (meaning that less fuel is being used overall) even though the throttle is pushed further open.