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Old 10-21-2008, 06:38 PM   #21 (permalink)
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Firing order is not the same as movement. Pistons move in pairs, but spark plugs don't fire in pairs. More here...

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Old 10-21-2008, 10:38 PM   #22 (permalink)
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Quote:
Originally Posted by thefirebuilds View Post
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.
chevy uses this lifter deactivation
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Old 10-21-2008, 11:23 PM   #23 (permalink)
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THE LAST WORD: Engines are compressors

Back in the early 70s, I came across an abandoned mining claim once where the old timer had converted a straight 4-cylinder engine to obtain compressed air for his mine. I took a look at the plumbing and stared at it for the longest time, trying to make sense of it. He'd cut off the front of the exhaust manifold that collected the exhaust from the first two cylinders. And he'd brazed shut the hole to allow the remaining rear part of the manifold to carry away exhaust gas. He pulled the spark wires off the front two plugs and just left the plugs in. He'd taken the front part of the exhaust manifold, turned it around and brazed an iron pipe to the hole he'd cut in the manifold, and ran the pipe to an air tank!

I describe this to illustrate that the internal combustion engine without combustion is an air compressor - and can be quite a good one if you delay the exhaust valve from opening until top dead center (TDC). The old timer couldn't figure out how to delay his valve so he got by on reduced compression.

Truck drivers, on the other hand, turn their diesel power plants into air compressors all the time. The Jake Brake shuts off the injector fuel flow and uses electric solenoids to delay the exhaust valve opening timing. By compressing air with the engine cylinders, you can slow down a 40-ton truck pretty good.

So forget about the easy fix myth for ecomodding engines by stopping the spark or fuel delivery. You gotta pull the piston. Otherwise you're running an air compressor - and that's not going to give you the mileage gain you're looking for.
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Old 10-21-2008, 11:29 PM   #24 (permalink)
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THE LAST WORD: Engines are compressors

Back in the early 70s, I once came across an abandoned mining claim where the old timer had converted a straight 4-cylinder engine to obtain compressed air for his mine. I took a look at the plumbing and stared at it for the longest time, trying to make sense of it. He'd cut off the front of the exhaust manifold that collected the exhaust from the first two cylinders. And he'd brazed shut the hole to allow the remaining rear part of the manifold to carry away exhaust gas. He pulled the spark wires off the front two plugs and just left the plugs in. He'd taken the front part of the exhaust manifold, turned it around and brazed an iron pipe to the hole he'd cut in the manifold, and ran the pipe to an air tank! When he cranked it (it had a magneto), it fired on two cylinders and ran pretty good.

I describe this to illustrate that the internal combustion engine without combustion is an air compressor - and can be quite a good one if you delay the exhaust valve from opening until top dead center (TDC). The old timer couldn't figure out how to delay his valve so he got by on reduced compression.

Truck drivers, on the other hand, turn their diesel power plants into air compressors all the time. The Jake Brake shuts off the injector fuel flow and uses electric solenoids to delay the exhaust valve opening timing. By compressing air with the engine cylinders, you can slow down a 40-ton truck pretty good.

So forget about the easy fix myth for ecomodding engines by stopping the spark or fuel delivery. You gotta pull the piston. Otherwise you're running an air compressor - and that's not going to give you the mileage gain you're looking for.
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Old 10-22-2008, 06:20 PM   #25 (permalink)
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Quote:
Originally Posted by Ptero View Post
So forget about the easy fix myth for ecomodding engines by stopping the spark or fuel delivery. You gotta pull the piston. Otherwise you're running an air compressor - and that's not going to give you the mileage gain you're looking for.
It's only an air compressor if there's a restriction on the exhaust or intake.
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Old 10-22-2008, 06:57 PM   #26 (permalink)
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It's an air pump if there's no restriction...
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Old 10-22-2008, 08:20 PM   #27 (permalink)
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I bet you could do this in a VTEC or other sliding / adjusting cam engine by making the secondary lobe wholly round on the exhaust side, so when it slides over it just opens the exhaust port. You could knock a 4 down to a 3. VTEC engines are pretty easy to adapt to a flip-switch situation, rather than driving off of RPM as they come from the factory.

The cost will be in the head.

How is a ZETEC engine? is it variable cam timing or a moving cam like in a Mazda CCV?
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Old 10-22-2008, 10:29 PM   #28 (permalink)
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Quote:
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It's an air pump if there's no restriction...
An air pump involves changing the pressure AFAIK, which doesn't happen for the most part w/ an unrestricted engine.
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Old 10-22-2008, 10:35 PM   #29 (permalink)
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I haven't accessed data re: pressure changes while motoring dead cylinders. I'd have to think, though, that there was a reason the OEMs all adopted valve shut-off strategies. You are saying that isn't necessary? Then they added cost and complexity where they didn't need to.
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Old 10-22-2008, 11:57 PM   #30 (permalink)
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Quote:
Originally Posted by Frank Lee View Post
I haven't accessed data re: pressure changes while motoring dead cylinders. I'd have to think, though, that there was a reason the OEMs all adopted valve shut-off strategies. You are saying that isn't necessary? Then they added cost and complexity where they didn't need to.
Emissions y0. Even though they can just shut off a bank and ignore oxygen sensor output for the deactivated one, the cat will favor HC compared to NOx at leaner mixtures, so they need to keep the exhaust stream at stoich. I suppose they could use some funky exhaust routing to do this but it's easier just to deactivate valves.

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