Lean Burn -vs- Cylinder Drop
 

Just brainstorming here. I'm about to move my '89 BMW 325i into the modern era with a Megasquirt 3/Expanded, which, amongst many other things, will allow me to run sequential fuel injection and wasted-spark (or COP) ignition. I also noticed while I was setting up the initial tuning, that there are options to drop random cylinders per event (i.e. remove fuel pulse from 2 cylinders per revolution), as well as dual-mapping (i.e. one "normal" fuel map, hot-switchable with another map tuned to whatever AFR I choose).

Assuming no cost difference between the two, and ignoring the detrimental effects of a lean-burning engine on a catalytic converter (because this is a "theoretical car" that I drive 40 miles a day in with no catalytic converters), What's the general consensus on Lean Burn vs Dropping random cylinders?

and... I just noticed that I've never posted here before (????)

Hey guys! I'm Jeremy. I fix (and build) BMW's for a living. I should say, for the sake of "full disclosure" that I drive fast and hard. I'm not a hypermiler by any means, but if I can make 500 horsepower and still get 25-30 MPG, I'm a happy guy. If I can get it to 50 mpg, I'll be a rich guy. ;)

Welcome. My understanding is that the cylinder cut out thing gains milage by reducing pumping losses. It makes the displacement of the engine smaller, therefore the throttle has to open more, thus your pumping loss goes down. Since pumping losses are not a huge loss to begin with, you are not likely to realize a very dramatic gain.

If you can physically deactivate the intake and exhaust valves on the cylinders to be cut out, then cutting out cylinders is viable. Otherwise, stick to just doing lean burn.

we cut cylinder activation by removing fuel pulse, so if we're removing 2 cylinders out of 6, we gain 33% economy (excluding the pumping loss of compressing the cut cylinders) right off the bat, plus the lower pumping loss of the "more open" throttle body.

In theory yes, but in practice no, you wouldn't see a 33% improvement but cutting only fuel to 2 cylinders (and not closing keeping both valves shut). The amount of energy required to pump air into the "dead" cylinders, compress the air, and then pump it back out through the exhaust negates a lot of the gain. You may still see a small improvement, but the biggest bang-for-your-buck would be lean burn.

When factory engines de-activate cylinders, not only do they cut fuel, the also close both the intake and exhaust valves creating an 'air spring' inside the cylinder. It takes energy to compress the air during the upstroke of the piston, but some of that is regained on the down stroke. This is the most efficient way to do it, and even in these applications, cutting 2 cylinders from a V8 does not result in 25% more fuel economy, because there are energy losses in the system.

I KNEW THIS WAS COMING!!! :eek: :rolleyes:

...but I'm gonna be super nice and refrain from posting what I really think.

Nice?

How the hell is that nice?

Stop teasing us Frank and tell us what you think! :D

Okay... Who are you? And what have you done with Frank?

Yes, like piston and ring friction losses and so on.

If you check out engines that have used cylinder cutout, the economy gain probably less than 10%. And this is for a V-8 switching to four cylinders on the highway.

I don't typically follow this closely, because the gains are not as large as lean burn, which I have in the Insight.

The lean burn gain is more like 20% or so.

Jim.

I never thought of it this way to tell you the truth. If I had, I'd have thought to myself...why stop at 2 cylinders, lets cut out 2 more and just run on the last 2 and get 3 times the mileage because if we only use 1/3 of the fuel, that means we go 3 times farther than before, so yer right, you'll get about 75-80 MPG by deactivating more cylinders.

Seriously dude...it takes a certain amount of power to go a certain speed, if you reduce the number of cylinders, you now must make more power with the remaining cylinders to keep moving, this means more fuel is dumped into the remaining cylinders than before, so fuel consumption remains about the same.

I'm now guessing that my pumping losses statement must have blown through your head at the speed of sound. I suggest you do research on pumping losses, and truly understand their impact. Be able to discuss it intelligently, then come back and make further comments, till then we're all gonna need sunglasses while viewing this thread.

http://thenewspatroller.com/wp-conte...sunglasses.jpg

wow, guys... really? Don't be dicks. I'll read more about pumping losses when you learn to... well... read the WHOLE statement.

1) You have identical pumping losses due to compression in EITHER scenario, assuming the valves are operated via camshaft only (i.e. no hydraulic/pneumatic/electric actuators).

2) You have to give more throttle input in EITHER scenario due to less power development, which slightly increases fuel flow to the active cylinders, but reduces pumping loss across the throttle body. (And for the sake of clarity to the people who are just learning reading comprehension, in a lean burn setup, it is still less than running stoichiometric.)

To the Lean Burn guys, I'm leaning that direction (no pun intended) already, but considering both routes because of the damage that a lean-burning engine can potentially (theoretically) do to a catalytic converter if spark is not re-tuned to compensate.

Do it, test it, report the results to us please.

Let me Google that for you!

Let me Google that for you!

Hey thanks for the links to threads I've already read. Were you referring to the "what happens if I pull two rods/pistons/valves/spark plugs out of my engine?" (i.e. the "bad idea") threads, or the "VW gets a 16 mpg gain by disabling 2 (out of 4) cylinders via fuel injection"?

TONS of bad ideas and bad information on this site along with tons of good stuff. I suppose for some reason I was hoping to find someone who was at least partially knowledgeable about BOTH systems without this turning into a bunch of fanbois with no real knowledge... and at best, I'd have been happy with someone who'd actually tested both systems on similar cars.

Since it's obvious that no one in this thread has much positive information to share, I shall venture out on my own (and do exactly what Frank Lee suggested and test both). I would say that I'd report back with my findings, but nahhhh... you guys do what you want.

Oh no, now I shall forever wallow in ignorance. :(

Alien dude. I was just having a little fun with ya. Your statements above still depict a woeful ignorance about how cylinder deactivation and pumping losses work. I and others here are simply trying to not so subtly tell you that, but you seem unwilling to believe anything that you don't guess to be true to begin with.
I can assure you with 100% certainty that cylinder deactivation on an engine not highly engineered to operate that way will yield awful results. The fundamental process that explains why it is doomed is the concept called pumping loss. This is why I say learn about what this is and what its implications are before you try to move ahead.

In my post, I addressed your idea, and explained why it wouldn't give you the results that you hoped for. I did not intend to come off as insulting or negative in my post, and if I did, I apologize, that was not the intention. I was simply trying to address your questions and inform you since I was not sure how much previous knowledge you had on the subject. I also run a lean burn equipped car (1994 Civic VX), and have done a ton of reading on cylinder de-activation. There are some even more (incredibly) knowledgeable people on this site. If you would like any input or help, I don't think calling us a bunch of fanboys with no real knowledge is the way to get it.

Meh. Alien d00d has already given himself an out - he's never going to post any results of his no-doubt brilliant plan to deactivate several cylinders without also deactivating said cylinders' valves. He can't state how his wonderfully crafted plan will somehow be different than all of the other failed attempts to cut fuel and/or spark from cylinders to achieve the same thing that he wants to do.

Oh, well.

I'm not as smart as some of the folk here when it comes to engine operation, but, I will attempt to 'splain to you (alien) what they are saying.

Every engine has pumping losses which consume energy. In a normally operating engine each piston rewards you by going boom every other stroke to give back more power than they consumed during the other 3/4 of their cycle.

With a proper cylinder deactivization setup, the deactivated cylinders stop being power hungry air pumps. They don't go boom, more like boing, boing, boing (spring sound). This means the still active cylinders have to pick up the slack for the others, but little more. Those cylinders that are no longer pulling the wagon are in it, but, they're rather light. In your scenario, they are in the wagon and they are dragging a foot over the side. So, yeah those cylinders still working are working a hell of a lot harder than before. Not "slightly" harder as you claim.

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

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.

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.

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.

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

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

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.

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

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

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.

How do we know you're not a troll, vago?

http://ecomodder.com/forum/attachmen...1&d=1361649181

a). I've made almost twice as many posts as you, pete c. b). I've given out almost 6 times as much thanks as you have. c). I've been thanked almost 4 times as much as you have, in over 3 times as many posts as you have. d). My compound curve aerocap's been featured on EM.com's blog. e). I donated money to EM.com.

I think I've proven my point about trolls.

I wasn't trying to troll. Simply wondering the pros and cons, and if anyone had tried it. Pete, this was exactly the answer I was looking for, so thank you.

I opened my membership a year and a half ago, but I admit I rarely spent any time on the forums. I apologize for not being able to sort through the pages (literally thousands of entries) on the subject to find my answers (amidst all the "can I just take the piston out and run it like that and get thousands of MPG?" threads.)

So FINALLY, after three and a half pages of scoffing and mocking the "retarded new guy who thinks he knows everything", I get two real answers. Thanks.

no, but thanks for the psychoanalysis. And thanks to Pete for showing some information from someone (who presumably has experience) that has proven me wrong.

You should have put some of that EM donation money towards a sense of humor. :D

Good on you for donating. I think you've shamed me into doing the same.

You're welcome, troll. :D

My sense of humor was surgically removed when I joined the Navy, and they never gave it back when I got out.

A fellow squid! Thanks for your service. What did you do?

I am still a reservist. Did 6 years as a surface ET about a 100 years ago.

They tried to stomp out my sense of humor as well, but, I've managed to nurse it back to health.

And I'm trying to be nice. See, lying works both ways.

See, now I know you're lying.

http://ecomodder.com/forum/attachmen...1&d=1361650470

The very first page of that Google search, that you scoffed at, would have given you the very answers you were looking for.

Many people on this thread gave you answers. They just didn't fit with your "Megasquirt/3 Expanded" derived cylinder deactivation idea from your "building" BMWs for a living.

Thanks. I was a sub nuke officer, and got out after it became apparent that I'd have to have my head surgically inserted into my rectum, in order to advance. Surface ET, eh? What ships were you on?

Still trying at my end, I'm afraid - I make do with sarcasm and backhanded comments.