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Old 10-03-2010, 01:17 AM   #1
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VX question

So, as I was doing some maintenance today i couldn't help but ponder two questions;
1. Is is possible to modify the stock ECU or modify the harness/ send a 12v+ signal to a specific pin or a ground, etc. so that lean burn is active all the time that a switch is on? I would like to experiment with lean burn at middle and full throttle instead of just the limited 1/4 throttle or less. It would be handy if you were on the highway and needed to ascend a small hill without losing lean burn. I'm thinking that if it was switched, you could use it like a "tow-haul" button featured on many GM trucks. (with the lean burn off)

I don't want to get into a new ECU. I don't have the scratch for that kind of work. I suppose excess heat might be an issue? Running that lean all the time at greater throttle? I also suspect that at some weight, rpm, etc that full time lean burn would HURT fuel economy. Examples would be during passing, hauling a heavy load, accelerating from a stop or up an on-ramp.

So, next question;
2. What are the negative ramifications of such a modification? Would this actually help FE? My thought is that right now in lean burn, pumping losses are greatly increased because I can only the throttle plate open a little bit. Further, in lean burn it's very difficult to get to high rpms (which is where most of the power is). With all time lean burn, I could reduce pumping losses in this way and get to higher revs when needed for climbing hills.


Obviously, this couldn't have been an option for a production car. Nobody even bothers to look at their temp gauges these days. Also, it likely would not want to be used during warm up either.
I'm thinking a shifter mounted push button would do the trick. Keep it close for passing and unexpected maneuvers.
I lack the technical expertise from the ECU side of it to figure this one out on my own.
Any thoughts?
Thanks
B
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Old 10-03-2010, 10:14 AM   #2
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Re: VX question

Doesn't look like you can do it - Wikipedia

Honda lean burn systems
One of the newest lean-burn technologies available in automobiles currently in production uses very precise control of fuel injection, a strong air-fuel swirl created in the combustion chamber, a new linear air-fuel sensor (LAF type O2 sensor) and a lean-burn NOx catalyst to further reduce the resulting NOx emissions that increase under "lean-burn" conditions and meet NOx emissions requirements.

This stratified-charge approach to lean-burn combustion means that the air-fuel ratio isn't equal throughout the cylinder. Instead, precise control over fuel injection and intake flow dynamics allows a greater concentration of fuel closer to the spark plug tip (richer), which is required for successful ignition and flame spread for complete combustion. The remainder of the cylinders' intake charge is progressively leaner with an overall average air:fuel ratio falling into the lean-burn category of up to 22:1.

The older Honda engines that used lean burn (not all did) accomplished this by having a parallel fuel and intake system that fed a pre-chamber the "ideal" ratio for initial combustion. This burning mixture was then opened to the main chamber where a much larger and leaner mix then ignited to provide sufficient power. During the time this design was in production this system (CVCC, Compound Vortex Controlled Combustion) primarily allowed lower emissions without the need for a catalytic converter. These were carbureted engines and the relative "imprecise" nature of such limited the MPG abilities of the concept that now under MPI (Multi-Port fuel Injection) allows for higher MPG too.

The newer Honda stratified charge (lean burn engines) operate on air-fuel ratios as high as 22:1. The amount of fuel drawn into the engine is much lower than a typical gasoline engine, which operates at 14.7:1?the chemical stoichiometric ideal for complete combustion when averaging gasoline to the petrochemical industries' accepted standard of C6H8.

This lean-burn ability by the necessity of the limits of physics, and the chemistry of combustion as it applies to a current gasoline engine must be limited to light load and lower RPM conditions. A "top" speed cut-off point is required since leaner gasoline fuel mixtures burn slower and for power to be produced combustion must be "complete" by the time the exhaust valve opens.
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Old 10-03-2010, 10:37 AM   #3
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Re: VX question

Quote:
Originally Posted by benfrogg View Post
So, as I was doing some maintenance today i couldn't help but ponder two questions;
1. Is is possible to modify the stock ECU or modify the harness/ send a 12v+ signal to a specific pin or a ground, etc. so that lean burn is active all the time that a switch is on? I would like to experiment with lean burn at middle and full throttle instead of just the limited 1/4 throttle or less. It would be handy if you were on the highway and needed to ascend a small hill without losing lean burn. I'm thinking that if it was switched, you could use it like a "tow-haul" button featured on many GM trucks. (with the lean burn off)

I don't want to get into a new ECU. I don't have the scratch for that kind of work. I suppose excess heat might be an issue? Running that lean all the time at greater throttle? I also suspect that at some weight, rpm, etc that full time lean burn would HURT fuel economy. Examples would be during passing, hauling a heavy load, accelerating from a stop or up an on-ramp.

So, next question;
2. What are the negative ramifications of such a modification? Would this actually help FE? My thought is that right now in lean burn, pumping losses are greatly increased because I can only the throttle plate open a little bit. Further, in lean burn it's very difficult to get to high rpms (which is where most of the power is). With all time lean burn, I could reduce pumping losses in this way and get to higher revs when needed for climbing hills.


Obviously, this couldn't have been an option for a production car. Nobody even bothers to look at their temp gauges these days. Also, it likely would not want to be used during warm up either.
I'm thinking a shifter mounted push button would do the trick. Keep it close for passing and unexpected maneuvers.
I lack the technical expertise from the ECU side of it to figure this one out on my own.
Any thoughts?
Thanks
B
#1 Question.
Its possible by running a management system and making your own maps. I have done this on a few cars. I can ascend most smalls hill around where I live at 17:1 A/F. But when it comes to high load you will need to run a richer A/F for thermal management reasons to keep the engine from killing itself.

#2 Question.
It could hurt the engine if the tune wasn't dead on. If the tune is good it would help FE over a stock VX. The stock VX is very limited as far as when lean burn mode is enabled.

Your question about pumping losses is correct in that if you could open the throttle plate more and keep it in lean burn you would see gains in FE. The problem is that a NA engine has fuel atomization issues at mid to heavy load. This can be overcome by utilizing a turbo charger to help the fuel atomize evenly throughout the whole cylinder and combustion chamber. This is the biggest hurdle I'm trying to figure out a way to overcome in my new NA engine. My turbo charged engine was way easier to dial in and much better when it comes to FE. I'm very disappointed in my NA engine at this time just for this reason.
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Old 10-03-2010, 07:49 PM   #4
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Re: VX question

Okay, so that basically answers both of my questions, thanks guys!
One last question is this:
Would it be possible to use a rev/load sensor to disengage lean burn rather than using a throttle position? It would be handy to have that throttle plate all the way open even if lean burn would only be on up to a certain rev/load. I suppose with a turbo and mapping anything is possible...
I've got an old mitsubishi turbo from my old 87' volvo 740 wagon available... been looking for a new home for that baby for a while.
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Old 10-04-2010, 06:09 AM   #5
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Re: VX question

load it typically read from the throttle position or, as becoming more common now, an calculation of VE....essentially the same thing but taking into consideration rpm.

the problems with extended or high rpm lean-operation are emissions and engine internal longevity. running that lean at more than 1/4 throttle is going to skyrocket NOx to start with, and might have prolems with missfires from too lean for a given throttle opening. as for engine damage: you will melt a piston or burn a valve before the temp gauge budges.

the honda stratified charge stuff is engineered around being NA. you introduce a turbo, and all the stratified charge stuff might go out the window. also too lean+boost=boat anchor. IF you did it, the best thing would be to re-spring the wastegate to limit boost to just a few psi (if any over atmo) to reduce pumping losses at part throttle without actually doing positive pressure (power=gas). I'm not saying don't, I'm saying you're gonna have to be really careful or it'll backfire. oh yea, and it'll take 50 years driving the car to realize a profit from FE on adding the turbo
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