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Old 09-11-2010, 06:23 AM   #1 (permalink)
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Join Date: Jul 2010
Location: Melbourne, Australia
Posts: 236

bugler - '91 Mazda 626
90 day: 35.89 mpg (US)
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idea, 4 cylinder to 2 cylinder engine conversion

I am thinking about changing my 2.2L 4 cylinder engine to a 3 or maybe even 2 cylinder. The car at the moment can accelerate with plenty of energy to spare, I could easily drive without any issue with ¾ the power that I currently have.

I have seen one or 2 posts about the idea on here and I have done some general research but I am trying to see if anyone has actually done this before as there are significant risks that I can see at the moment and if I do it wrong I may damage the engine and have to get a new car.

From what I have found a 4 cylinder engine is balanced so that during each piston stroke there are 2 pistons going one direction with 2 pistons going the other direction essentially cancelling out any motion that would unbalance the engine.
So going down to 3 cylinders would have the issue of 2 cylinders going up while 1 goes down in which case due to the inertia change the engine will vibrate. Standard 3 cylinder engines get around this a bit by having different angles and firing timing which would be very difficult for me to do on an existing engine. I could try it out just removing one cylinder and see how it goes but im likely to have a very shaky car and vibration may damage things.

The other alternative is converting my 4 cylinder to a 2 cylinder. There are some 2 cylinder cars around not very popular though. My car can apparently generate 115 hp with the 4 cylinder so it would make sense that a 2 cylinder would give 57 hp which I figure would be enough to run a car on, wouldn’t accelerate too quickly though.
There is something I am concerned about though, the 2 cylinder engines are inherently unbalanced because although 1 cylinder goes up and 1 goes down which cancels out the inertia but it then creates a rotating force because the 2 cylinders can’t be in the same location and any offset causes rotational forces.
Another possible issue is that with 2 cylinders which have cylinders going in opposite directions is that the firing sequence will be uneven. A 4 cylinder engine fires all cylinders in 2 rotations so 720 degrees. Each cylinder will then fire every 180 degrees, when deleting 2 of the cylinders AND making sure each cylinder goes in the opposite direction the only way to do this causes one cylinder to fire at 180 degrees then the other to fire at 360 then for angles 540 and 720 (or 0)there will be no cylinders firing 0 power. I am worried this will mean the engine will have to idle faster to cause enough inertia to keep rotation going while the engine rotates from 360 to 720 degrees.

So my question to the group is, has anyone tried this since I still want my car to work when im done I’d like to know if anyone has tried and failed or succeeded.
If anyone has tried it or if anyone has a 2 cylinder engine do they have significant engine vibration?

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