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Old 10-16-2008, 05:15 AM   #11 (permalink)
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that's an interesting thought. i believe your camry has a firing order of 1-4-3-2, with 1 and 4 firing at the same time, and 3 and 2 firing at the same time.

so my thought is mechanically, you could remove 2 of the pistons and rods, say 1 and 3. this would open the combustion chamber in to the crankcase now, so you would need to disable the valvetrain of the same two cylinders. the easiest way i can think to do this would be to grind the cam lobes so they are not opening the valves.

the question i have is would a twin cylinder have enough power to push the car down the road. maybe maybe not, but unless you have a lot of time and even more money, i wouldn't go to the trouble of trying.

all of this is mechanical i am not sure what would have to be done with the ecm to make it work, but i am sure it would not be easy.

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Old 10-16-2008, 12:35 PM   #12 (permalink)
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Originally Posted by gofastbobby View Post
that's an interesting thought. i believe your camry has a firing order of 1-4-3-2, with 1 and 4 firing at the same time, and 3 and 2 firing at the same time.
I don't see why any engine designer would do that. You want to make the engine run smoothly, which means spacing the firings at equal intervals. 1 & 4 might be at TDC at the same time, but one should be on the compression stroke, the other on exhaust.
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Old 10-16-2008, 01:24 PM   #13 (permalink)
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Originally Posted by jamesqf View Post
I don't see why any engine designer would do that. You want to make the engine run smoothly, which means spacing the firings at equal intervals. 1 & 4 might be at TDC at the same time, but one should be on the compression stroke, the other on exhaust.
eh, good point.
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Old 10-18-2008, 01:33 PM   #14 (permalink)
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So could you put an inline switch on the wires going to the injector, so at highway speed, you manually flip the switch and kill one or more injectors?
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Old 10-18-2008, 08:07 PM   #15 (permalink)
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You can turn off fuel injectors with a switch. To protect the electrical system you should also install diodes that would prevent voltage spikes from reaching the computer. In my opinion, it wouldn't be a good idea to deactivate a cylinder unless you have to because a defect in one cylinder. I actually did that on a Ford Mustang with a 2.3 liter engine. The car didn't have fuel injection but I deactivated a cylinder by removing the rocker arms from the bad cylinder. It ran pretty well on the highway. It was a bit rough at low speeds. It ran too rich until I changed something in the carburetor. Maybe I deactivated a power valve somehow. The fuel economy was good.

I also deactivated a cylinder on a car like a Chevy Monza (Maybe an Oldsmobile Starfire) with a Pontiac 2.5 liter engine. It had a worn out exhaust cam lobe. On that engine I took out a pair of pushrods. The varnish on the bottoms of the valve lifters caused them to stick in the lifter bores after the engine was started. If they fell out it would have been a problem because of an internal oil leak that would reduce oil pressure. The engine wouldn't run with all the pushrods in because exhaust gases from the bad cylinder would go into the intake manifold and smother the other cylinders. It could be driven again with the modification.

You may not get any improvement in fuel economy if you just shut off an injector or two. You would also have to do two other things:

1) Close the valves in the deactivated cylinder to prevent pumping losses and a loss of oxygen sensor function.

2) Tune the fuel mixture. It is likely to go too rich unless you make adjustments.

The main reasons I don't recommend this are:

1) The car will shake a lot at low RPM
2) The exhaust pipe will probably break from the shaking
3) The engine mounts will have a short life
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Old 10-20-2008, 11:41 PM   #16 (permalink)
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Quote:
Originally Posted by jamesqf View Post
I don't see why any engine designer would do that. You want to make the engine run smoothly, which means spacing the firings at equal intervals. 1 & 4 might be at TDC at the same time, but one should be on the compression stroke, the other on exhaust.
Straight fours fire in pairs every 180 degrees, but due to the difference in piston speed between the pairs most modern straight fours also use a balance shaft. Straight sixes fire in pairs too but don't have this problem because they can fire every 120 degrees, so the fastest pair speed, even though there is still a slowest pair, is offset by the third pair moving a some speed in between.
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Old 10-21-2008, 01:08 AM   #17 (permalink)
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Also, closing the valves isn't required to reduce most pumping losses, at least those associated with part throttle operation.
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Old 10-21-2008, 02:21 AM   #18 (permalink)
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Quote:
Originally Posted by gofastbobby View Post
the question i have is would a twin cylinder have enough power to push the car down the road. maybe maybe not, but unless you have a lot of time and even more money, i wouldn't go to the trouble of trying.
Look at the Fiat 126p: it has a two-cylinder 650 ccm engine and its 24 hp rushes its 600 kilos from 0 to 100 KPH in just 56 seconds! It does shake, though, you can see the car's rear dancing in idle at a streetlight. FE is 5.2-7.2 l/100km ( 45-33 MPG).

In the case of a four-banger with two dead cylinders, I think it should be enough if you're using it only for cruising and not passing.
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Old 10-21-2008, 10:54 AM   #19 (permalink)
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one should consider pulling the rods and pistons will unbalance the crank causing excessive wear on the other moving components. I would assume that the production versions of these are simply forcing valves open to reduce friction resistance, obviously the cylinders aren't removed when disabled in those cars.
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Old 10-21-2008, 02:12 PM   #20 (permalink)
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Quote:
Originally Posted by roflwaffle View Post
Straight fours fire in pairs every 180 degrees...
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).

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