Converting 4cyl Nissan Altima to 2cyl - removing pistons and connecting rods
 

Dear friends in the ecomodder community, my name is Anatoly Kishinevski. I am a Russian engineer.

This thread is about a modifying a car engine to half of it's original displaced volume with the goal of increasing fuel efficiency drastically while maintaining driveability of the car (safely).

I have been planning the conversion of a 4 cylinder car to a 2 cylinder car for about 2 years. I recently acquired a rust free 2000 Nissan Altima with a 5spd transmission and 2.4L KA24 engine. This car is going to be the machine to which this modification and test is done. The engine is favorable because it has a very long stroke to bore ratio.

The idea is to remove two pistons and connecting rods. Typical firing order of a 4cyl engine is 1-3-4-2, so for this modification pistons 1 & 4 will be the ones I remove. Reason being, having pistons 2 & 3 remaining together will help engine stay as warm as possible. This will make the new firing order x-3-x-2-x, essentially the engine will fire-miss-fire-miss-fire-miss. It will be firing half as often as it normally would.

I have heard of people doing variations of this modification, but not necessarily with the goal of increasing fuel efficiency. I have searched quite a bit and found very little information on anyone else who has attempted this for the sole purpose of fuel efficiency. I have been very interested to see how well it works and if the car is still driveable. I anticipate it will be. Any comments or thoughts that you have on this process will be greatly appreciated. Please feel free to add constructive comments, questions, etc. below.

Points of consideration in this effort:

a.) engine will be off balance- Because pistons 2 & 3 move in phase e.g. move up and down at the same time. This lack of balance may be bearable without any effort to correct it, however I expect the car will vibrate quite significantly. To correct the lack of balance, doughnuts of very dense metal, for example wolfram (tungsten), may be manufactured and clamped onto the crank journals where the connecting rods have been removed. This would probably help with balance, but also introduce harmonics the engine was not originally designed to deal with.. it will probably work fine either way.

b.) oil pressure- If two connecting rods are removed from the crankshaft/engine, then something needs to be done to block the oil passages on the crank so oil pressure remains adequate. The best solution would be to cut the connecting rods to keep their original bottom on the crankshaft. This would maintain factory tolerances and oil pressure. Alternatively, using a hose clamp and some sheet metal would probably suffice.. or using epoxy or threaded insert into oil passage.

c.) valves of cylinders with missing pistons- The camshaft lobes for cylinders where pistons are removed will have to be ground to base circle so that the valves are no longer opening on disabled cylinders. Easy task

d.) MAF sensor (mass air flow sensor) will see incorrect amount of incoming air- It is possible the air/fuel maps programmed in the ECU would be able to accommodate the significantly reduced volume of air, however possibly not. In order to correct this problem, if needed, a venturri or reduced cross section tubing can be used in intake to compensate. The MAF sensor would be placed within this reduced diameter intake pipe. You can make the MAF sensor think that the same volume of air is passing by it as if there were still 4 cylinders pulling air in. To monitor air fuel ratio a wide band will be installed.

e.) lumpy power distribution- Due to the engine firing half as often with only 2 cylinders, it may feel lumpy in it's driving throughout various RPMs. To correct this, a heavier flywheel can be utilized. This will cause the engine to run smoother. For the initial attempt the stock flywheel will be used.

f.) fuel injectors- Fuel injectors on cylinders with missing pistons need to be blocked. In order to keep the computer happy and prevent it from knowing the fuel injectors aren't actually doing anything, instead of removing them, fuel compatible epoxy will be used to block them off. Then the computer can still fire them, but no fuel will be passing through.

g.) cooling capacity of stock system would be too great- The engine with only two cylinders may not be able to get up to full operating temperature with stock cooling system. In order to remedy this utilization of an under-drive water pump pulley may be helpful. It is possible the thermostat alone will be adequate.


The power of the engine will be measured on a dyno before this modification takes place.. and then the power will be measured after the modification takes place.

This whole project stems from the problem with cars being geared poorly with no consideration for fuel economy. Even in 5th gear in a normal car, on the highway when you stomp the gas, you can still accelerate at a considerable rate. Instead of dealing with taller tires or trying to figure out how to re-gear the car, if you simply reduce power output, then you can maximize use of the transmission's gears ;)

I would be very happy to hear people's thoughts on this. I will continue to provide updates as the project progresses.

Sincerely,
Anatoly Kishinevski

I put quite a bit of thought into doing just this, and almost pulled the trigger. However, the car is running well so "If it ain't broke, don't fix it" ruled the day.

I believe it would work but the fuel economy gains would not be as great as hoped/estimated.

Frank Lee, thanks for the reply. I agree there will be fuel efficiency gains, however it is hard to estimate what the real increase will be. I do expect what you say is reality.. that the gains will not be as great as hoped. I am expecting a positive result overall. Soon we will know hard numbers.

I believe the most significant design aspect for tuning the result is the mass of the flywheel.. I think it is important for averaging out the two power strokes and "smoothing" operation of the engine.

Do you think firing two pistons sequentially and then missing two, essentially like a V-twin motorcycle engine would render greater drivability contrary to the fire-miss-fire-miss pattern I initially proposed?

Any other thoughts on this project, will be happy to hear.

I would have probably just ground down the camshaft for the valves associated with cylinders 1 and 4. That is, assuming that the valves were directly driven off the camshaft instead of using a rocker arm or some other method of articulation.

The pistons inside cylinders 1 and 4 would effectively turn into springs, as they continually compressed and then let expand the air trapped inside them. You would also still have all of that mass to offset the 180 degree out-of-phase mass of the pistons and conrods for cylinders 2 and 3.

Anatoly, welcome to the forum.

You may be interested in this thread:

http://ecomodder.com/forum/showthrea...lly-21753.html

Seems to me like you'd put in a lot of time, effort, and money for a small fuel efficiency gain at the expense of anemic performance and potentially huge problems of balance and engine management issues, not to mention reliability problems. I see fuel efficient Honda Civics on craigslist here in my area all the time that are just needing a little work on the tranny or engine. For what you'd spend on your mod there you could have something that gets 38mpg, works great for many miles, and many years.

If you're the mad scientist type and just wanna do something because you can, than by all means. As a practical/money saving project.....I think you'd be better off putting your time and money into something else. My 2¢, maybe worth that, maybe not.

Dear MetroMPG,

I greatly appreciate your response. In response to what you have expressed, I had the same thought process and indeed have attempted this same experiment/modification already on a 1986 Nissan Sentra wagon. That car, which has a favorable stroke to bore ratio, as Nissan's typically do, had solid rocker arms and a single overhead cam. In order to deactivate the valves on pistons 1 & 4, I cut and ground the rockers so they were only a spacer keeping the rocker assembly in proper spacing. Valves for pistons 1 & 4 were no longer actuated as the rocker arms were nothing more than sleeves/cylinders on the rocker shaft when I was done with them.

I anticipated that the pistons with the deactivated rockers would act like air springs.

What I found was the engine was very under powered... almost undriveable. There was a narrow RPM range in which it produced enough power that the car could run safely, however it was overall very poor performance.

I theorize that the "air spring" effect is actually more complex than the initial conception realizes. What I mean by this is that in consideration of fluid dynamics/acoustics, there must be very specific RPM in which the pressure wave inside the cylinder is not working against the deactivated piston. At the speeds that the piston is moving, the resistance of an air pressure wave can be considerable. With respect to wave mechanics, you may generally have constructive interference or destructive interference in considering the phases of the oscillations in whatever system you are working with.

In short, I found the engine could not perform suitably.

It is possible either the engine or transmission were already worn beyond a usable limit, however before I modified the engine I did drive the car and it seemed to operate reasonably. I also always make sure to refresh the transmission whether it is an automatic or manual with fresh fluid/oil.

Also, I am aware that several manufactures have incorporated this "cylinder deactivation" feature in their engines.. so that 8cyl engines can operate as 6 or even 4 cylinder engines via control of a computer. It seems that friction effects are probably significant enough that benefit from this feature is minor or negligible. I have seen no hard evidence that cylinder deactivation or the air spring effect offers useful results, either in literature or from my own experimentation.

Again, I am only one data point. Maybe it is worth repeating this experiment.

Thank you for your response MetroMPG.

-Anatoly Kishinevski

I wouldn't mess with "air spring cylinders" at all. They are still an energy loss, albeit a smaller energy loss than inactive cylinders pumping air through them. I think the performance would be more acceptable, but still far less than what we are used to, with piston deletes.

If the compression ratio in the "air spring" cylinders were to be lowered I suspect that you might get a useful efficiency gain.

One way to do this might be to remove the inlet or exhaust valves and then block the port downstream from the valve.

Another option would be to fit pistons with a lower piston pin to crown height.

The lower compression ratio would allow one of the compression rings to be removed thus reducing mechanical friction.

I think those are fails.