Thread: Running 3 Cylinders

Just curious as to how damaging it would be to the engine to run on only 3 cylinders (one bank) in the various ways you can go about it, e.g. simply cut the injector pulses, or go further and run 2 TB's with a custom intake, etc, etc.

The background behind this: I've been throwing the idea around for a while now about a custom PCM (I have the time and knowledge/ability to gain the knowledge, as well as know others that are experts in the necessary fields whom I can gain knowledge from) and was thinking about how someone said that you could build a 30mpg city 3800 if you really put your mind to it (I know it was a generic theoretical statement, but it's still probably true). Anyways I'm not shooting for anything super ridiculous like 50 or 60mpgs city, but I figured since these engines are pretty simplistic in design, it would be easier to modify them than other engines (plus I'm already familiar with them). So...basically the idea is to have 3 modes of driving -- eco, auto, and performance. Eco will force the engine to run on 3 cylinders instead of 6, auto will switch to 3 cylinders at cruising speed in OD, and performance will force 6 cylinders all the time. Other modifications to support this kind of system is a custom twin turbo setup to dump boost separately if needed, or single turbo setup.

Other random details about this PCM are that it would be open source and would offer free open source tuning software (obviously you will still need to buy the necessary hardware though).

So, I'm ready for the flame and the "JUST GO BUY A DIFFERENT CAR"s. Bring it on bishes. I would like to get some legit input on this though, as 97-03s can be had for cheapsies, and microprocessors are rather inexpensive nowadays as well (plus, well, I'm a programmer so the OS and software are cake :P).

no damage will be done if some cylinder are shut off

Originally Posted by matt5112

the research i'm proposing is to look at the GXP.

And what sort of fuel savings they see from disabling DoD.

Elaborate? Also, the different modes would basically have different tunes as well that would need to be taken account for. Any system variable is programmable, so whatever would help save gas can be programmed into the OS. We're limited only by the hardware and the imagination that determines how to use it.

Originally Posted by matt5112

don't DoD motors have a different firing order to compensate for this?

Im saying no damage as in, because there is no fuel and spark it cant damage it because it still does its normal functions just without fuel.

I think the firing order is changed too

The firing order can be whatever it needs to be, all that matters is that you average the load throughout the crank. For instance, instead of going 1, 2, 3, 4, 5, 6, you would fire 1, 3, 5 or 2, 4, 6. Correct me if I'm wrong.

So pretty much the firing order for 3 cylinders would have to be 1, 5, 3 or 4, 2, 6.

All sources I have read indicate that the firing order is 1-6-5-4-3-2, but whatever. The principle order is the same. I think I3 might be the best option for scaling down the displacement. Next issue -- shutting down air and fuel to the unused cylinders. Fuel is a no-brainer by shutting off the injectors, and I was thinking separate air intakes for each bank. And disengaging valves isn't an option.

Also, what other improvements can be made through tuning to optimize for fuel efficiency? Even things that currently cannot be tuned for a specific condition.

Originally Posted by matt5112

lemme check... have a feeling you're right on that one.

I do know its dumb.

edit: and so am i, you are correct.

Coils.

high volt, low current? fuel economy.

low volt, high current? power.

. <-------- that is the point




You are here ----> ___

The point of this is to be able to flip a switch and go from economy to performance. If you mod physically for economy, you cannot flip a switch and magically have the economy parts replaced with performance parts. By controlling all the economic and performance options via computer you can (because software can change dynamically whereas physical parts cannot). Why do you continue to use fallacious arguments? They don't follow the guidelines of the requirements.

Let's pretend that I've unhooked or switched a couple wires around in the past. Our engines aren't the smoothest missing two cylinders. Maybe there's a way to balance that out based on which cylinders you disable. Where's the engineers to tell us which ones. I'm not confident that 3 cylinders will be enough power and smooth enough. I'm ready to see you try and help where possible though.

Also keeping in mind that as each cylinder hits, it contributes to the rotation, so maybe disabling every other cylinder that fires is the way that will work the best.

im thinking bill is in the right thought train here. running one bank seem like it will be entirely too hard to control. maybe you just use every other cylinder (1,4,5)?

Running one bank would be firing every other cylinder though. Here's an illustration of the firing order along with the firing order for running a single bank:



You can tell where each piston is going to be in its rotation based on the firing order because a cylinder only fires when a piston is at a certain point in its rotation.

wont running on 3 cause the engine to work 2x as hard thus negating any advantages or saving fuel?

Originally Posted by tylerbinski

wont running on 3 cause the engine to work 2x as hard thus negating any advantages or saving fuel?

The only time you really need the full power of the engine is during acceleration. Under cruising circumstances you only usually need about 70hp. So no.

Wouldn't closing off air to the "off" cylinders create massive negative tourque when the downward moving piston creates a vacuum? Why not let air flow through and help cooling?

Firing order cant be changed aside from swapping compression and exhaust strokes correct?

How rough would it run?