How to make my 4 banger a 3 cylinder

[Frank Lee]

I would've guessed they'd re-route the exhaust/re-locate the O2 before messing with the valvetrain...

[roflwaffle]

Even if they relocate the O2 the catalytic converter will still get a very lean exhaust stream and will favor HC instead of NOX (orthe other way around), so emissions increase disproportionately. I suppose they could reroute exhaust from the deactivated cylinders back into the intake for the same result but they would have to partition the intake as well as have additional plumbing/switching from the deactivated runners, which takes up more space and requires more to take apart for repairs. The deactivate valvetrains seem pretty simple these days so I can see why a manufacturer would go w/ 'em.

[Frank Lee]

Dual exhaust?

[roflwaffle]

Is it cheaper to pay for an entire extra exhaust, including redesigning the vehicle to accommodate it, or just some bits in the head?

[Duffman]

What cylinder deactivation is doing in the simplest theoretical terms is redirecting the air from one bank to the other since the engine still requires the same amount of power to go down the road. The increased load on one bank reduces that sides pumping losses, since the other bank is not moving any air there is no pumping losses other than heating up the air that always stays in those deactivated cylinders. Theres no messing with O2 sensors AFAIK because there is either no flow over them or the flow doesnt change depending on where they are located.

[CobraBall]

Originally Posted by some_other_dave

Huh? The firing order on most Honda I4's is 1-3-4-2. Nowhere do two cylinders fire at the same time.

I can't think offhand of any I4 engines that fire in pairs. Most fire one cylinder every 180 degrees of crankshaft rotation, which is every 90 degrees of camshaft rotation--one quarter of a full two-crank-revolution "cycle". I think you may have gotten confused by the difference between the two (which is regrettably easy to do).

-soD

A complete cycle (intake, compression, power, exhaust) on all 4 cycle engines is 720 degrees or two revolutions. 4 cylinder engines fire every 180 degrees for a total of 720 degrees. 6's (even fire) -120 degrees, V8s-90 degrees

[red91sit]

Originally Posted by Duffman

What cylinder deactivation is doing in the simplest theoretical terms is redirecting the air from one bank to the other since the engine still requires the same amount of power to go down the road. The increased load on one bank reduces that sides pumping losses, since the other bank is not moving any air there is no pumping losses other than heating up the air that always stays in those deactivated cylinders. Theres no messing with O2 sensors AFAIK because there is either no flow over them or the flow doesnt change depending on where they are located.

As far as the heat goes, it only increases in heat under compression, under decompression it absorbs a lot of that heat back into the gas (air).

[CobraBall]

Suggest reading. Crankshaft Balance Factors

It discusses in detail the various forces that act on the rotating mass of a 4 cycle engine. If you go from a 4 to a 3 cylinder, be sure to carry several containers, some kitty litter, a push broom and a shovel in your 3 cylinder car. The kitty liter to soak up the engine oil when the rod(s) go through the oil pan. The broom to sweep up the engine parts and kitty litter and the shovel to put the mess in the containers.

[Ptero]

You think you've got problems? At least you can go to 2 cylinders. All I've got are a straight 5-cylinder turbocharged Volvo engine (72-degrees) and a 3-cylinder Smart engine (120-degrees). I'M SCREWED!!! Maybe I can glue them together and disconnect something...

[Frank Lee]

Originally Posted by CobraBall

Suggest reading. Crankshaft Balance Factors

It discusses in detail the various forces that act on the rotating mass of a 4 cycle engine. If you go from a 4 to a 3 cylinder, be sure to carry several containers, some kitty litter, a push broom and a shovel in your 3 cylinder car. The kitty liter to soak up the engine oil when the rod(s) go through the oil pan. The broom to sweep up the engine parts and kitty litter and the shovel to put the mess in the containers.

I doubt if anything that drastic would happen. You'll tire of the awful exhaust note and vibrations long before the engine blows up.