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Old 05-15-2013, 01:26 PM   #31 (permalink)
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There's no way to deactivate just one cylinder on a carbed engine via the fuel system. By playing with fuel mixture on the fly you would be making the entire engine run leaner

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Old 05-15-2013, 03:26 PM   #32 (permalink)
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Quote:
Originally Posted by Phantom View Post
Unless you have two O2 sensors one for each bank more common on v8s and some v6s, the ECU will see lean and dump more fuel to get it to 14.7.
Unless I'm remembering some other thread, the OP has a header and the O2 sensor is only installed on one of the exhaust pipes, so it is only fed by a single cylinder.

Measuring AFR won't tell you anything about how much fuel is being burned, unless you also know how much air is coming in. And measuring it on a single cylinder's exhaust when you are disabling a different cylinder tells you even less about overall fuel consumption.

If you have an MPGuino, you can get a reasonable idea of how much fuel is being burned. You need to tap into the signal for a non-kill injector, then multiply the fuel usage by 0.75 because only three injectors are working when the one cylinder is killed. Chances are that the MPGuino raw readout will go up, but if it does so by less than 1/3, then you have a fuel savings.

The SG and UG options might be quite inaccurate for this usage, because they estimate fuel used from a bunch of other parameters. And shutting down one cylinder violates at least some of the assumptions made for this calculation, rendering is much less reliable as an estimate of fuel usage.

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Old 05-15-2013, 03:55 PM   #33 (permalink)
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I'm running a vx swap and my afr gauge is reading all 4 cylinders. Its tapped into the lower side of the converter. So the 17:1 ratio is an average of those 4. The 3 that are running are still probably around 14.7 but the one that's pumping oxygen in with 0 hydrocarbon is changing the average to lean.

Remember I only tried this at idle because there are less variables, there's no change in tps, map, iat, egr. So you can expect the same result every time you do it. When ur driving everything changes and has a different fuel trim relating to what throttle position, load, coolant temp. Etc so its unpredictable.

I'm curious to see what happens when Stacy gets it going, who knows maybe itll work.
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Old 05-16-2013, 02:34 AM   #34 (permalink)
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If you wanted to get involved in this, to take care of the pumping losses, you could have someone machine a spacer with another throttle plate in it on teh two cylinders you deactivate typically. Wire a solenoid into the same switch so that when the cylinder injectors are inactive, it also kicks the throttle plate closed for those two cylinders.

You'll still lose some from the cylinder pulling vacuum against those plates, as well as friction losses from driving the valves still, but you won't be sucking/squeezing/[not]banging/blowing, anyway.
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Old 05-16-2013, 02:45 AM   #35 (permalink)
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Might wanna do the exhausts too. Aw heck, just do the regular valves.
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Old 05-16-2013, 02:48 AM   #36 (permalink)
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I was thinking that plugging the intakes off would basically negate any need to do the exhausts... since nothing would be flowing through anyway. The only time I've ever actually tried it was on a bench 2cyl 2 stroke though. If I capped one carb and removed the fuel line, nothing would come out of the exhaust on that side and it was obviously running crappy from only having one cylinder while still spinning two.
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Old 05-16-2013, 02:55 AM   #37 (permalink)
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I'm trying to imagine the flows w/an intake butterfly; seems to me if a valve is open and the piston is moving, flow is gonna happen even if it is mainly just in-n-out through the exhaust valve.
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Old 05-16-2013, 03:02 AM   #38 (permalink)
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Exhaust valve is only open on the up stroke... if there's nothing to push, nothing is gonna come out.

There'll be like an atmosphere of vacuum against the new throttle plate in the spacer, so /some/ flow is going to still get by, but it's gona be far reduced from original flow.
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Old 05-16-2013, 03:06 AM   #39 (permalink)
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Quote:
I was thinking that plugging the intakes off would basically negate any need to do the exhausts... since nothing would be flowing through anyway.
The intake, compression and power strokes will happen with a vacuum, but towards the end of the power stroke, when the exhaust valve opens, gas would rush into the empty cylinder. The last upstroke, would then be done with pressure acting on the piston.

Cancelling one up and one down stroke with vacuum, leaves us with one down stroke with vacuum and one up stroke with pressure, netting a significant loss.
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Old 05-16-2013, 12:54 PM   #40 (permalink)
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Quote:
Originally Posted by jakobnev View Post
The intake, compression and power strokes will happen with a vacuum, but towards the end of the power stroke, when the exhaust valve opens, gas would rush into the empty cylinder. The last upstroke, would then be done with pressure acting on the piston.

Cancelling one up and one down stroke with vacuum, leaves us with one down stroke with vacuum and one up stroke with pressure, netting a significant loss.
I was going to use butterfly valves on the intake side of a V8 engine, in my own cylinder deactivation idea, which is documented here. This was a project supported more by wishful thinking than by thermodynamics analysis, which I could have done even then, but didn't.

However, due to the reason that jakobnev just mentioned, I abandoned this idea. Have you ever tried to pull on a piston to create vacuum? It's pretty frickin' hard to do.

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