Lean Burn -vs- Cylinder Drop

[baldlobo]

a better analogy would be;

say you have a carriage being pulled by 6 horses, well two of said horses are dead and being dragged, the question is will the other 4 die before you get to where your going. if you keep on going they will need to be feed more, alot more; in order to keep dragging the dead bodies around

ps. that doesn't include the fact that the o2 sensor will probably read lean as hell, and you'll see none of the benefit of killing said cylinder

[pete c]

OK, I think we've beaten this dead horse enough. [rimshot]

That is an equally good comparison and good point about the O2 sensors going nuts and making it run very rich.

[AlienBlood]

har. beating a dead horse. Agreed.



btw, as an aside, I encourage you all to consider the cycles of an engine, and how those cycles change in all three scenarios - stoichiometric, lean burn, and deactivation (fuel-based, without changing valve operation). "Pumping loss" is a phrase that seems to be thrown around on this forum quite a bit, without realizing that it is purely a mechanical function. Whether a cylinder is running at 9:1 or 19:1 AFR, its pumping losses are identical. The only difference in the entire cycle occurs in the power stroke (when it goes bang), which, still, does not affect pumping loss.

I understand that keeping the valves closed (i.e. an air spring, or "boing boing boing") will reduce pumping losses on the "dead" cylinders, but it's not, theoretically, a requirement (just a "better?" way to do it with unlimited funding). Then you only have to worry about warping cylinder heads and exhaust manifolds.

There is SO MUCH more involved in how an engine works that I can't and won't type it here. I started this thread assuming that people here would know the intricacies, and was sorely mistaken. For that I apologize.

I appreciate the people who tried to give helpful advice (2000Neon, you're one of them, so don't worry about being bulked in with the others), but I think I'm going to start brainstorming with people I know who, like me, actually have experience with enginebuilding, fuel and spark tuning, and diagnostics, instead of coming to forums like this one. After all, it's literally 5 clicks of a mouse to test either method and come up with a conclusive answer..... and a year of driving to see if either method will damage anything (which is really the important reason for starting this thread in the first place).

As I said, I trust that you will all continue doing whatever suits you best, and I will do the same. I'll cross my fingers that you don't break anything, even if you won't give me the same courtesy.

Have fun.

[AlienBlood]

Originally Posted by pete c

good point about the O2 sensors going nuts and making it run very rich.

None of this would be possible without a fully programmable ECU checked by a wideband O2 sensor. It's a very (and I mean VERY) simple matter of tuning the engine to run stoichiometric, then to run on the stored fuel map during Economy mode (effectively ignoring the O2 sensor).
Lean burn would be almost as easy. Tell the ECU to center and "learn" at 18 or 19:1 AFR on a secondary fuel map, and tune spark to compensate. Map switching is possible based on throttle position, load, or RPM, whichever your preference.

[slownugly]

Go to a mega squirt forum and state your case there. Not many people on here (to my knowledge) use mega squirt, or venture off into the deactivation realm. You are going to be met with skepticism.

That bein said my opinion is that lean burn is the only way to go. You have that completely tune able fuel injection, use it to create 18-20:1 afrs at a light throttle low load condition and adjust timing accordingly. Hopefully the engine can handle it. If you start shutting the injectors off without doing anything else, how is that any different than having an injector that fails and creates a misfire on a normal engine. Make 2 misfires and it's going to run like total crap in my opinion

[pete c]

slownugly, don't question alien. he builds engines and stuff.

[pete c]

Alien, in case you're still lurking out there, i have one more question.

If there was some sort of benefit to merely shutting off an injector, why hasn't it been done? I mean we're talking about a free mpg improvement, right? A few lines of ECU code and viola, an improvement in mileage!!!

Actually, there is such a system, or was, anyway, with the caddy V-8 a few years back. It was called limp home mode where it did what you are proposing, shut off fuel to half the cylinders in the event of a cooling system malfunction, essentially turning it into an aircooled engine.

I suspect there is some data out there on mpg numbers running in this mode. I bet they suck.

[pete c]

Originally Posted by some dude on a caddy board with over 10K posts who sounds like he knows what he's talking about

There are other things done with the idle speed, fueling, spark advance, etc. in concert with the cylinder cut out but the main function that makes the limp home system work is the cylinder cut out. Remember, the valves are still operating so the cylinder still pumps air thru it...making it an internally air cooled engine when in limp home mode. This is often confused with the DOD (displacement on demand) system upcoming on GM engines and the older V-8-6-4 system on the 81 Cadillacs. They are not the same as the Northstar limp home mode. In DOD the valves are actually disabled so that they stay closed to disable the cylinder. Just turning off the fuel to disable a cylinder causes huge pumping losses that are immediately evident trying to drive the car. With only 4 cylinders running and 4 dead but still pumping the engine has the net output of about 1.5 cylinders as much of the power goes into the pumping loss of the dead 4 cylinders. In DOD, the gases trapped in the cylinder act as an air spring returning the power used to compress them to he piston on the down stroke.

Found this on a caddy board. Sounds like a real bad idea.

[Frank Lee]

I don't think he does much lurking; he's had over a year to discover the volumes EMers have written on it already.

[t vago]

Alien d00d is what I like to call a "troll." He's simply trying to get a rise out of people, who would then post items to try to prove Alien d00d wrong. It's a novel, if annoying, method of doing research.