Cylinder Deactivation?

[enkeivette]

I'm trying to think of a reason that would prevent me from setting up my own cylinder deactivation mode with a switch.

To me it seems that all you would need to do would be to setup a switch that would cut spark at the spark plug wires and cut the electricity to the fuel injectors. You'd have to think about which cylinders to cut to keep the engine balanced but that would be easy.

Am I missing something here? The only problem that I could see with this is that it might trip the 02 sensor out, half of the cylinders would be pumping atmosphere out the exhaust. But that's the only problem I could see with this. It wouldn't trip the knock sensors out... Am I crazy?

[SeanPlunk]

Yeah, I don't think you'll notice the difference between 8mpg and 6mpg that much :huh:

[enkeivette]

I get 20+ on the highway wise guy.

And I'm talking about the Neon. Wouldn't work with the Vette, the carb dumps fuel at the top of the manifold, so there is no way to regulate it between cylinders. But the Neon injects the fuel into the manifold right above the cylinder.

Now that I think about it, there might not even be a need to cut spark. If there is little to no fuel in the chamber it wouldn't matter... I think? Might be as simple as hooking up two of the fuel injectors to a switch.

[SeanPlunk]

Let me get this straight, you want to cut your 4 cylinder down to a 2 cylinder? What the hell is wrong with you? Just go buy a Vespa or a Segway if you care so much about gas mileage :nutkick:

[SeanPlunk]

P.S. I strongly endorse your project, PLEASE, PLEASE take pictures - I can't wait to see the results.

[enkeivette]

Let me get this straight, you want to cut your 4 cylinder down to a 2 cylinder? What the hell is wrong with you? Just go buy a Vespa or a Segway if you care so much about gas mileage :nutkick:

Yesss. It doesn't take 150 hp to keep my lil 2500 pounder at a constant speed on the highway.

Take pics of what? Splicing a wire? I'm really not even sure that this would work, but someone's done it before.

[Vettezuki]

Yesss. It doesn't take 150 hp to keep my lil 2500 pounder at a constant speed on the highway.

Take pics of what? Splicing a wire? I'm really not even sure that this would work, but someone's done it before.

You aren't making anywhere near 150 BHP at a constant speed on the freeway, unless it's at peak HP somewhere in the vicinity of Red Line. Try more like 40 (or less). Reduce by two cylinders and you'll be making well less than half of that, probably not enough to maintain freeway speed. Remember, your remaining two cylinders (4 stroke cycle) not only have to do enough work over time (power) to maintain a constant speed against drag, etc., but have to compress the two deactivated cylinders and spin the whole rotating assembly. My guess is that if it worked at all, you'd be finding yourself at higher revs to make similar power and not save any fuel, while increasing wear on the engine. This is my hypothesis. Please test and report. :)

[enkeivette]

You aren't making anywhere near 150 BHP at a constant speed on the freeway, unless it's at peak HP somewhere in the vicinity of Red Line. Try more like 40 (or less). Reduce by two cylinders and you'll be making well less than half of that, probably not enough to maintain freeway speed. Remember, your remaining two cylinders (4 stroke cycle) not only have to do enough work over time (power) to maintain a constant speed against drag, etc., but have to compress the two deactivated cylinders and spin the whole rotating assembly. My guess is that if it worked at all, you'd be finding yourself at higher revs to make similar power and not save any fuel, while increasing wear on the engine. This is my hypothesis. Please test and report. :)

The engine spins at 4K rpm at 80mph, the speed at which I typically cruise on the freeway. You really think my engine is only making 40hp at 4K rpm?

The best thing to do would be to get a custom 5th gear made to put me around 2500rpm at 80mph. But that would be a PITA and I'm not even sure how I'd go about it.

But the reason I posted this thread, I was looking for flaws in the actual mechanics of my plan. Would this work? Am I missing something? Would it in fact trip the 02 sensor out? What do you guys think?

[Sonic03SVT]

The computer would absolutely lose its mind. It would be registering insufficient fuel flow, failing injectors, a massively lean condition, as well as an ignition fault. If youre lucky, youd end up with a check engine light. If unlucky, "limp" mode and horrible mileage. Also, your 02s measure lean, and the computer will add fuel...meaning your remaining 2 cylinders would run really rich, besides that, youd have to alternate cylinders, as without fuel going into the remaining two cylinders i think youd find theyd get REALLY hot REALLY fast, fuel really being the only thing that cools them. You may lose valve seats or scuff cylinders. Intriguing idea though, itd be neat to see if it could be made to work.

[enkeivette]

Failing injectors is something that did slip my mind, can't think of a way to get by that. And I figured I could fix the 'massively lean condition' or O2 sensor problem with a resistor. But I guess it's not happening now.

Out of curiosity though, about the fuel keeping the piston cool, I wouldn't think that it would be a problem. Without the combustion happening I would think that the oil and coolant would be enough to keep the piston cool, wouldn't you? I mean, it seems to work for Dodge.

[Sonic03SVT]

I suppose you're right, the friction alone from the moving cylinder shouldnt heat it up too badly. This idea has always intrigued me, and id love to figure out some way to make it work, Id like to know some details on what exactly Dodge is programming the computer to see, how they differentiate between an intended shutdown and a problem, as the ECM is concerned.

[Vettezuki]

I suppose you're right, the friction alone from the moving cylinder shouldnt heat it up too badly. This idea has always intrigued me, and id love to figure out some way to make it work, Id like to know some details on what exactly Dodge is programming the computer to see, how they differentiate between an intended shutdown and a problem, as the ECM is concerned.


The valves aren't open. You're still compressing air, and that makes it hot. The higher the compression, the higher the temperature. If you have enough residual heat and a little unburnt fuel (from a mis-timed deactivation) you could theoretically get one hell of a detonation.

I'm just guessing, but I suspect there are a lot of good technical reasons it took GM decades to get this technology ready for prime time. :huh: And in their reinfined applications on V8s, it *only* gains about 10% total fuel economy.

[enkeivette]

The valves aren't open. You're still compressing air, and that makes it hot. The higher the compression, the higher the temperature. If you have enough residual heat and a little unburnt fuel (from a mis-timed deactivation) you could theoretically get one hell of a detonation.

I'm just guessing, but I suspect there are a lot of good technical reasons it took GM decades to get this technology ready for prime time. :huh: And in their reinfined applications on V8s, it *only* gains about 10% total fuel economy.

That did cross my mind also, the instant you cut fuel, there may be enough remaining fuel in the chamber for one or two really lean explosions. This is probably why it would be best to cut spark at the same time.

[TimAT]

You'd still have the cylinder(s) that you cut pumping air, and that would add a bunch of load. GM tried that back in the 80's on a Caddy- the original 8-6-4. Problem was they just cut the fuel/spark to the ones they wanted off, and only did it in 4th gear with the convertor locked. Most of them, after a few miles, would shake like a possum passing a peach seed. If you could get the exhaust valve off the seat during the compression stroke you might have a chance.

[big2bird]

You'd still have the cylinder(s) that you cut pumping air, and that would add a bunch of load. GM tried that back in the 80's on a Caddy- the original 8-6-4. Problem was they just cut the fuel/spark to the ones they wanted off, and only did it in 4th gear with the convertor locked. Most of them, after a few miles, would shake like a possum passing a peach seed. If you could get the exhaust valve off the seat during the compression stroke you might have a chance.

Hold the phone. I remember solenoids on the rockers.;)

[TimAT]

Hold the phone. I remember solenoids on the rockers.;)

You're right-- CRS kicking in again, but that was what, like 1980? Bottom line was the system worked for a while and then went stoopid. We used to clip the wire going to the 3rd or 4th gear switch on the trans to fix it. Lots easier (and cheaper) that trying to fix the system.

[big2bird]

You're right-- CRS kicking in again, but that was what, like 1980? Bottom line was the system worked for a while and then went stoopid. We used to clip the wire going to the 3rd or 4th gear switch on the trans to fix it. Lots easier (and cheaper) that trying to fix the system.

Yep 81 was the next great failure. 4100HT. I had one. POS.:judge:Remember? It had the alum block with iron cylinder sleeves, held in with o-rings? No one would touch it for a rebuild.

[Vettezuki]

You're right-- CRS kicking in again, but that was what, like 1980? Bottom line was the system worked for a while and then went stoopid. We used to clip the wire going to the 3rd or 4th gear switch on the trans to fix it. Lots easier (and cheaper) that trying to fix the system.

I didn't know there were any solenoid activated rockers on any production vehicle. Or am I misunderstanding. Were the solenoids on the 12v system or did they have a separate 40+V system? As you know, automotive companies have been kicking around the idea of a fully electronic valve train to get all the advantages of infinitely programmable valve timing, optimizing power, torque and emissions through all rpms. I guess they just haven't been willing or needed to go that far yet.

Lots of mechanically trick stuff going on with variable valve timing from many of the makers now. Did any of the makers ever consider pneumatic valves like in F1 cars?

[TimAT]

All the solenoids were supposed to do was lift the valves on the selected cylinders off the seat. And in those years it was all 12v.

[big2bird]

I didn't know there were any solenoid activated rockers on any production vehicle. Or am I misunderstanding. Were the solenoids on the 12v system or did they have a separate 40+V system? As you know, automotive companies have been kicking around the idea of a fully electronic valve train to get all the advantages of infinitely programmable valve timing, optimizing power, torque and emissions through all rpms. I guess they just haven't been willing or needed to go that far yet.

Lots of mechanically trick stuff going on with variable valve timing from many of the makers now. Did any of the makers ever consider pneumatic valves like in F1 cars?

You have it right. Google Cadillac 8-6-4.
I beleieve the latest tech is solenoids deactivating the hydralic lifters. (You young guys would know).