Getting the most out of lean burn (Honda)

[serialk11r]

Originally Posted by Cobb

Alright, lets see how long the motor lasts. I had a supercharged tacoma with the v6 and trd charger. This was before they added the 7th injector. I was doing between 15-17 to 1 ratios and once at a dyno pull they stopped it claiming I had seriously fuel issues and needed to get it checked or a piggy back system.

15-17 is pretty dangerous at high load because the peak temperature is slightly higher than stoich, which is usually already dangerously high (though EGTs won't increase much past stoich because less heat of combustion = less heat leftover), but by the time you get to 18:1, peak flame temperature is already down, and at low load it's not an issue at all. Aside from the fact that there's some excess oxygen that can possibly burn away the lubricating film and such, but oil that gets into the combustion chamber is pretty much done for anyways.

[MN Driver]

Originally Posted by turbovr41991

Has anyone ever listed out the lean burn differences between the VX, HX, and insight? From what I can tell with the HX, I can have lean burn all the way to 3,100 rpm.

On a personal side, I struggle to engage lean burn if I am not around 2400 - 2500 rpm, under 20% throttle, under 70 LOD, and on a warm engine. Are these 4 factors what limit lean burn?

I am really interested in this work. I know there are also alot of HX and insight owners that would could benifit from this!

Haven't driven a VX or HX but my 1st Gen Insight will hold lean-burn up to about 32TPS if you are under 70mph but you need to cut back to about 26TPS to reliably hold lean-burn where it cuts out at 78mph(~2800RPM 5th gear). Cuts out between 85-90LOD depending on RPM and the cars mood that day. Requires 154 degrees or higher coolant temp. I just drove from Minneapolis to Southeast Missouri and holding the 75mpg lean-burn only usually gets you 60-65mpg on the flat with no or favorable wind and temperatures warmer than about normal room temperature. Cooler, uphills, wind, etc and you might struggle to get beyond 55-60 and many hills pull it below 50mph if you don't drop out of lean-burn. There's not much HP at 75mpg. My overal MPG on the way there was 76.1mpg and the trip was 693 miles and took 11hr 15min. 61.6mph average speed.

To get into lean-burn with the Insight you need to drop to MPG meter to about 100mpg, wait about 2 seconds usually but up to 10 depending on the mood of the car. Every mile or so it drops out of lean burn for about 10 seconds to purge the NOx cat and then slinks back in on its own. If you drop out of lean-burn due to TPS sensor, shifting, letting off the throttle, or too much throttle you need to wait about 10 seconds while in lean-burn favorable conditions to get it to reengage at the 100mpg point. With all that being said, it's a PITA to try to cruise above 60mph on the highway with lean-burn with an Insight. Friend drove a leg of a long cross country trip at 85mph and we got 55mpg without lean-burn for a non-stop tank without the lean-burn, don't need it much though since the engine is at ~80% load in 5th gear at that speed.

The Insight seems a bit more complicated to modify its lean-burn considering that it's got more monitoring with the OBDII and is ULEV emissions with the extra NOx cat and lean-burn purge cycles. It seems to make more than just a few factors. Maybe not though, could be easier than I figure.

[seeodywhy]

Originally Posted by 1carnut

I have both a VX and an HX and there is a big difference in Lean Burn between the two. I would really like it if I could get the HX to behave more like the VX for starters and then ideally apply these changes as well. I have tried to read up here on LB and have had some dialogue with Brucepick who yielded some good information and the Marvel Mystery Oil tip. I've only been driving the HX for a short time but the HX seems to limit LB engagement until it's above about 1900 rpms where the VX did not. It also will not engage sometimes after it is warm under the same conditions that it normally would and I find that I have to run the speed/rpm's up really high (~70mph) and then it will engage again but only stay in LB down to about 65 mph. I'm looking for any additional useful information or suggestions.

I posted on here a while ago trying to find out the exact same thing. I would like to know if the 3 stage vtecs use lean burn more aggressively. I originally was thinking that I might run an hx engine off the computer for one of those. Does anybody know of the specifics. I also was hoping to ask what the differences are between the internals of the jdm d13b engines that show up on ebay sometimes and the hx. Are they bored bigger or did they play with the stroke.

[greasemonkee]

The D15B 3 stage vtec engines originally came with a one wire O2 sensor, maybe I've been missing something, but I don't see anywhere that the 3 stage was a leanburn from the factory. Nevertheless, the three valve mode has the potential to operate in leanburn to my knowledge. I almost bought this engine, but parts for an engine with Siamesed vtec spool valves?

For the skeptics claiming it will "melt" the engine to operate WOT in leanburn - Heat = pressure, thus pressure = heat. There literally is not enough of either to damage the engine. Combustion temps are cooler in leanburn producing 25 hp than at stoich fueling producing 25 hp. Flame propagation must be fast enough to minimize waste work (pressure before TDC), otherwise so much timing would be required that most of the energy released (pressure/heat) would be making the engine work against itself - the reason you can't just take any engine and expect it to run lean efficiently.

Combustion temps are known to be highest at stoichiometry and dropping off on either side of a lambda of 1. Only problem is the high oxygen content becomes dangerous at slightly-leaner-than-stoich ratios where temps are high, that is what will destroy an engine - if the heat isn't there, the oxygen is harmless.

I would be concerned about trying to squeeze off much more hp in leanburn, and I'm sure there is a point of diminishing returns somewhere along the line.









The HX engine would probably run fine on a P07 ecu, the timing tables would be out a little, but as long as the injectors were the same cc and you used the L1H1 O2 sensor it should work.



I'll look into making a fuel log, some days require a rush where I could care less about economy so to see the numbers on a graph may appear like a sawblade.

[seeodywhy]

The 3 stage was definitely a lean burn motor. I was inquiring if anybody knows of the rpm's where lean burn engages because the ecu is pretty much plug and play in the hx except for the second vtec solenoid.

[turbovr41991]

Originally Posted by seeodywhy

The 3 stage was definitely a lean burn motor. I was inquiring if anybody knows of the rpm's where lean burn engages because the ecu is pretty much plug and play in the hx except for the second vtec solenoid.

Plug and play with the HX? Please explain more.

[seeodywhy]

The three stage vtec is obd 2 with a 1 wire o2 sensor. It doesn't have a vtec oil pressure switch and but it has an extra vtec solenoid, I figured that all you would have to do is put a resistor in there. Japan has way more lax emissions standards. In addition, in japan the car powered a four door and supposedly got better fuel economy than our hx's. Several guys on on honda sights who put these in hatches for speed with ex tranny's swear they still get 50 mpg highway. The gearing in their trans' is definitely not as tall as ours. My dream was to mate the 3 stage ecu with vx tranny and hx head and the d13b. Everyone who uses those motors are almost always the racer types so I haven't found anything about when lean burn engages. The manual p2j ecu's show up on ebay every once in a while but they can be pricey.

[seeodywhy]

I have a digital copy of the manual somewhere. I'll have to look for it the next time i'm in Baltimore.

[Jakins]

D13b would be so awesome. On that note, could you convert a d15z1 to obd2 by using an obd2 harness and p2j ecu and 5 wire o2?

[seeodywhy]

No because there are more sensors on an obd2 motor. It would be easier to buy a conversion harness and then run the couple wires to run an obd2 motor with the vx ecu. The p2j doesn't use a 5 wire sensor. It would work just because the signal wire attaches to the same ecu pin for both cars. There is a d13b on ebay right now. It's in montreal I think. I drove there to get a motor I bought off ebay for a 300zx tt I used to have. The problem is that the guys who sell them don't know anything about them. I would have gone that route but a y5 engine tranny and all accessories dropped into my lap for 400. There is a guy in Indiana who gets them sometimes too.