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Old 09-14-2010, 11:11 PM   #31 (permalink)
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With two cylinders not producing any power, that leaves much more loading against the two that are producing power, which changes the transitional piston speed during the power stroke, and results in the lugging.
Spark advance would need to be reduced to match this increased work load and slower piston acceleration. You will also likely need to increase the stall-speed of your torque converter and/or up the stall-torque ratio inside the converter. That part is not usually easy or cheap unless you can find one that already fits your need, and fits your vehicle.

IMO, it's best to keep the ECM in open-loop mode when testing a drastic change like you're doing. Even if closed-loop functioned perfectly during your test, stoich just isn't going to cut it when you're trying to accelerate with only two cylinders. Also, if you're not data-logging, then there will be far too many unknown variables in your experiment and probably a little too much speculation when it comes to the results.

I think this is interesting and I don't want to sound discouraging, but you know if it were very easy to do, ...

I like the idea, but it's hard for me to imagine being able to pull it off on a shoestring budget. If I were trying this experiment, I'd want to go through the engine thoroughly before-hand, eliminating the cam followers, rods, and pistons on the dead cylinders, and epoxying up the dead ports in the intake manifold, - make sure all open oil passages were either plugged or rerouted as necessary, and add weight to the flywheel or install a looser converter.

As for the crank, I have had to lighten the counterweights for performance rods/pistons before. It's relatively easy, though a little more weight would need be ground off in this case. I have my V8 cranks balanced for usually $150 or less - usually less if they don't require added weight. Tapping and plugging the oiling holes in the crank pins would also be easy. Oil pressure and delivery to the remaining bearings would actually be improved, possibly allowing a reduction in volume from the pump.

I would use a stand-alone for engine management, or an older GM ECM in case the required tuning parameters were such that the code had to be patched. The increased pulsing in the intake manifold would probably require extra smoothing (filter routine) to calm down the MAP output at lower RPM. The throttle body would also need to be physically downsized in order to preserve any sort of part-throttle resolution in both the spark and VE tables.

This is all bench-racing though. I have a couple of spare four cylinders, but no time for such an experiment in the near future.

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Old 09-15-2010, 11:07 AM   #32 (permalink)
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What could be done to help eliminate the issue of additional pressure/pumping loss from the deactivated cylinder is:
Remove the exhaust valve
Reroute the exhaust on those cylinders to open air

If you cant keep the spring in place to push back on the rocker this will not work and would not allow you to turn them on and off. By opening the exhaust side to open air it eliminates the compression of air and prevents it from slowing the expansion stroke of the firing piston. Also this will prevent the O2 sensor from seeing the extra air.

Plus it could sound cool.
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Old 09-15-2010, 01:56 PM   #33 (permalink)
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Quote:
Originally Posted by saand View Post
I guess the question is, has anyone driven a 2 cylinder engine that is a straight 2 and was it vibrating all over the place or smooth. If anyone can tell me it was smooth then this mod might be workable.
I've driven an older Suzuki GS500 and newish BMW F800, both parallel twins.
The Zuki is rather rough, especially at lower rpm.
The F800 is smoother, because of the fake 3rd pistonrod acting as a balancer, but still not as smooth as a 4-inline.



(Didn't ride these : )
Another reasonably smooth parallel twin is the Kawasaki 650 (W650, ER-6 range).
With more vibes - could have been designed in or simply not ironed out - there's the Triumph 865cc (Bonneville Thruxton America Speedmaster).

So in m/c applications, the inline twin is a well-proven concept.
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Last edited by euromodder; 09-16-2010 at 05:53 AM.. Reason: added some more recent production inline twins
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Old 09-15-2010, 08:32 PM   #34 (permalink)
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Euromodder thanks, good to know there are some 2 cylinder parallel twin out there that are smooth enough for production.
These are both on bikes though so i assume the RPM is higher at idle from a quick search about 1300 rpm so that might help reduce the vibration. Maybe if i go to 2 cylinder i do need to up the idle RPM so the engine doesn't shake itself apart and if i remove 2 cylinders and all their losses and increase the RPM by less than double i will have a fuel saving anyway.

Olympiadis thanks for all the good suggestions, given me a few ideas for when/if i try this out. I am hoping i dont have to change the ECU or get a custom one but will see how i go.
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Old 09-17-2010, 02:02 PM   #35 (permalink)
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have you tried disabling cylinders 1 and 4 or 2 and 3? You'll be suprised at how the ECU will adapt to the new idle requirements. Most good ECUs will raise the idle requirements to compensate for the lack of power.

Earlier, you mentioned you disabled cyl 1 and 2. So your power order was no power, power, power, no power, no power, power, power, etc.

If you'd disabled cyl 1 and 4 or 2 and 3 it would have been power, no power, power, no power, power, no power, etc. Something tells me an intelligent chap as you will see the advantage of the second pattern adverse to the first.
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Quote:
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I think you missed the point I was trying to make, which is that it's not rational to do either speed or fuel economy mods for economic reasons. You do it as a form of recreation, for the fun and for the challenge.
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Old 09-17-2010, 05:33 PM   #36 (permalink)
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My "experiment" in cylinder deactivation.

I had a 1962 VW beetle, the original air-cool horizontally opposed 4 cylinder boxer engine. It had a lot of miles. One day I'm driving along, and the engine suddenly makes this horrendous banging sound for about ten seconds. Then the horrible noise quits, but the engine runs very rough.

The top of the piston basically broke off at the ring groove, and the main part of the piston, hammered the piston crown up into the chamber until it couldn't hit it any more. This had several effects:

1. No pumping losses, since the top of the piston is effectively missing.
2. Less balance problems than the OP is considering. Just the top of one piston is "missing", not entire pistons and rods.
3. In 1962, there were no monitoring electronics or computers, just a carburator.


The original engine made some pathetic low number of horsepower, like 50, and with the one cylinder deactivated, it could barely get out of it's own way. And the vibration, particularly at certain speed was...ominous.

I drove it that way for a couple months while I built a new engine. I don't recall any improvement in FE.

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Last edited by solarguy; 09-17-2010 at 06:16 PM..
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Old 09-17-2010, 08:28 PM   #37 (permalink)
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There a lot of things working against ya, the whole intake and exhaust system is optimized for 2.2L , running only 1.1L and intake manifold plenum and TB are to large along with exhaust system pipe diameter .

While the ECU will try to keep idle rpm at 800-850 (whatever stock spec is ) a 2 cylinder would probably need at least 1000 -1200 to get flow velocity up a bit .
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Old 09-17-2010, 09:50 PM   #38 (permalink)
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Hey saand, a few thoughts:

I've seen this tried a few times, esp. with VW engines cut down to two-cyl opposed units, that was especially to fight the unbalance problem. It didn't double the mileage. Mileage did increase, but only because the incredibly underpowered engine was pushing a custom super lightweight car.

If you're going to run on just two cylinders, run on the middle two. I think that will reduce shaft whip along the crank vs. trying to fire the outside two. It separates the firing to every 360 degrees for a nice even beat. And the two adjacent hot cylinders help keep each other warm for better combustion.

I don't think there are many advantages to be found in removing the pistons in the disconnected cylinders. Obviously there are frictional losses, but leaving them in place means you can have your full engine output at a moment's notice - perhaps literally if you simply interrupt the injector controls with a dash mounted switch. Don't bother with cutting down the cam lobes either, for the same reason.

Weight reduction is key. Drag reduction is key. The more load you can take off the engine, the closer you can get to an optimum level of power output with your minimized engine.

But what everybody else is saying is also true. Your engine was built to work properly as a four banger. All the parts are intended to work together; taking a few parts out of the loop like this throws everything off. You may see some improvement after all's said and done. But once you've got the vehicle weight down to the minimum, and changed your driving habits to the thriftiest you can make them, hook the two cylinders back up. See if the mileage changes.
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Old 09-17-2010, 10:27 PM   #39 (permalink)
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Shadetree the firing order you mentioned has its benefits for more regular power and therefore should reduce lugging compared to the alternative. It does however have the disadvantage of worse balance as 2 cylinders will be going up and no cylinders will be going down.
There are trade offs for both methods and if i do progress with this mod (after changing to a manumatic) i will have to attempt both methods.
Also the ECU i have is from 1991 or probably designed a bit earlier so it doesn't appear intelligent enough to compensate the idle for the lower power. I can however tune the idle myself, i have been considering overriding the computer idle control as well as im an electronic engineer and i think i can give it a better response than the ECU does after i have made a few changes to reduce the idle level for the car in its current 4 cylinder state.

If i am just deactivating the injectors and opening up the air intake of the deactivated cylinders but leaving the pistons then definately the firing order you mentioned is the best as the unused cylinders will balance out the powered cylinders and the more regular firing order will help lugging.

elhigh your point about weight reduction and drag reduction is definately important. I had only considered this mod after reducing weight and drag (not as much as id like though). The car can accelerate with plenty of power to spare and it can maintain highway speed with power to spare. if i didn't then i wouldn't consider this mod.
I also like the idea of using the cylinders in the middle for localized heating keeping each other warm for good combustion and reduction in shaft whip

solarguy interesting to hear you were driving a 4 cylinder deactivated to a 3 cylinder for a few months must have been a wild ride. I have a friend at work that had the exact same experience of the piston breaking at the shaft only a month or 2 ago. You mention that you would have bad vibration at certain speeds, i assume this was due to vibration at a natural frequency of the engine since the removal of one of the piston heads caused a serious loss of balance rather than the engine lugging at a low RPM like i saw with mine during my very brief test drive.
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Old 09-17-2010, 11:11 PM   #40 (permalink)
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with half the cylinders dectivated on my 4 L v6 the idle did kick up a bit for certain.

I would plan on making deactivating half the cylinders an objective that can be activated or deactivcated in the cabin. Honestly, you need all 4 clylinders for take off and acceleration, but for cruising you only need to maintain speed, which on the flat land requires only cutting throught the air. According to my scanguage cruising only requires less than 50 hp of the possible 200 hp of the engine. This played out when I would deactivate half the cylinders once I got to speed in my explorer. SUre it worked, but if I had been a bit more ingenious with making the ecu "see" only half the o2 content present it would have worked absolutely awesome.

To make the ecu see only the relevant data concerning the activated cylinders had a plumbing or electrical solution. The ECU depends on the 02 sensor to detect the oxygen content in the exhaust stream. If you make the ecu detect only half the signal of the 02 when in cylinder deactivation mode, it won't "know" you have 2 cylinders deactivated. If the ecu only detects the o2 content of half the cylinders from the o2 sensor when in 2 cylinder mode, it will not "know" 2 cylinders are deactivated and the 2 running cylinders will be running at normal efficiency. Sure you will lose a bit of fuel moving the worthless cylinders (although it would help cool the engine) but you will be using less fuel per rpm.

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I think you missed the point I was trying to make, which is that it's not rational to do either speed or fuel economy mods for economic reasons. You do it as a form of recreation, for the fun and for the challenge.
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