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Old 09-13-2010, 11:40 AM   #21 (permalink)
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Patrick thanks for the suggestion, I dont have a great understanding of all the terms and the details of how an engine works but i think if i cut off the connecting rods on the pistons near the big end i would have issues. The big end which i think is the part of the piston that goes up and down the shaft (please correct me if im wrong) is used to guide the connecting rod so if this was cut the connecting rod would just rotate freely and likely smash into things in the motor.
I think there are counter balances for the pistons so if there are i could remove the counter balances which would stop some of the vibration but wouldn't stop it all. I think i have to deal with the fact ill have vibration, i can counteract vibration caused by lack of balance on the shaft but the vibration i will get from 2 cylinders which are offset from each other and will cause rotation is unavoidable unless the engine was completely different. Also i will have vibration from the no so ideal firing order

Edkiefer thanks for the firing order i was going to find this out by experimentation or when/if i open up the engine.
i agree there is risk of more fuel being used but i think without the loss of 2 cylinders the fuel used will be much less idleing and at highway speeds as a large part of my losses while coasting is just the engine rotating away at very low energy output levels.
Some things that may cause issues with this assumption is the ECU being untunned due to the changes but i think if it relies on keeping the O2 sensor happy and at stoic then shouldn't be too bad, in open loop though it will probably just burn lean which i guess is a good thing for efficiency.
Another thing is if the engine now has to run at higher RPMs to get the energy to accelerate and coast.

I do have a home made scan gauge (which uses the injector pulses for fuel info) which will tell me how much fuel i have used so i can do a before and after test. But i dont think it will work for the test that involves just pulling the injectors because air will still be pumped through the unfueled cylinders so if the car tries to keep stoic it will just put more fuel in the working injectors causing those cylinders to burn rich and inefficiently. Ill take some measurements anyway, if i get an improvement it will give me an idea.

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Old 09-13-2010, 05:46 PM   #22 (permalink)
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The "big end" is the "big end" of the connecting rod--the rod that connects the piston to the crankshaft. The notion being that you just leave the round part of the rod that goes around the crankshaft, and that's it. You have to be careful, though, as I'm not sure how much clearance there is around the crank throws. It'd be bad to have the left over bit of rod smashing the inside of the engine...

-soD
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Old 09-13-2010, 08:41 PM   #23 (permalink)
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Here a link on balancing that may give some info for those not familiar with the process .

Understanding Crankshaft Balancing: Engine Builder

There really not a lot of room around the rod ends on many engines (bottom of cylinder wall come down close to crank so so do the block walls , all to make block strong ) .

Your really going to have tough time removing rod/piston .
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Old 09-14-2010, 06:55 AM   #24 (permalink)
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Thanks edkiefer, good link explains balancing well. If others dont know if a 2 or 3 cylinder engine is "balanced" as described in the link in the last post by edkiefer it doesn't mean the engine will be free of vibration as other modes of vibration occur.

Well i tried out removing the injector signal to 1 and 2 injectors and it was an interesting ride. The car lugged a lot when accelerating up but if i was sitting at 70 kph it was drivable. I believe the lugging is because there is a dead spot in acceleration during a quarter of the cylinder cycle so less power therefore require higher revs to go to the next gear. My automatic car obviously didn't know this so every time it went up to the next gear it would lug. So i don't think i can go any further until i see if i can make a manumatic out of my auto.

In general besides the lugging it wasn't too bad i think when actually moving at speed i would barely notice the missing cylinder.

Not sure about vibration though which could compromise the life of engine parts.

So at this stage im going to look into changing my car to a manumatic and ill have to think about if i can deactivate a cylinder on the fly from the cabin. This would let me get up to highway speeds, deactivate a cylinder and reduce some fuel usage. The issue i have to think about is how to stop the pumping losses of the cylinder on the fly
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Old 09-14-2010, 09:58 AM   #25 (permalink)
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Quote:
Originally Posted by saand View Post
Thanks edkiefer, good link explains balancing well. If others dont know if a 2 or 3 cylinder engine is "balanced" as described in the link in the last post by edkiefer it doesn't mean the engine will be free of vibration as other modes of vibration occur.

Well i tried out removing the injector signal to 1 and 2 injectors and it was an interesting ride. The car lugged a lot when accelerating up but if i was sitting at 70 kph it was drivable. I believe the lugging is because there is a dead spot in acceleration during a quarter of the cylinder cycle so less power therefore require higher revs to go to the next gear. My automatic car obviously didn't know this so every time it went up to the next gear it would lug. So i don't think i can go any further until i see if i can make a manumatic out of my auto.

In general besides the lugging it wasn't too bad i think when actually moving at speed i would barely notice the missing cylinder.

Not sure about vibration though which could compromise the life of engine parts.

So at this stage im going to look into changing my car to a manumatic and ill have to think about if i can deactivate a cylinder on the fly from the cabin. This would let me get up to highway speeds, deactivate a cylinder and reduce some fuel usage. The issue i have to think about is how to stop the pumping losses of the cylinder on the fly
For sure 2 cylinder made from manufactures are balanced , like all the motorcycle engines , but that not going to stop them from vibrating Harley's are good example .

Your problem is you have 2 counter balance weights on the crank that you would not want (plus the rod journal )

Going from AT to MT would probably be much better improvement and easier . I forget, what speed is the AT on 626 , 4speed ? . If 5 speed MT is available that would be nice improvement .Better performance with improvements in mpg due to extra gear and less drivetrain losses .
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Old 09-14-2010, 10:17 AM   #26 (permalink)
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Quote:
Originally Posted by EdKiefer View Post
For sure 2 cylinder made from manufactures are balanced , like all the motorcycle engines , but that not going to stop them from vibrating Harley's are good example .
Harleys are a BAD example. Any decent motorcycle with 2 jugs runs smooth as silk. Harley has a crank that would be great if there were 3 cylinders, instead there are 2; ie, the rods are opposed by 120 degrees instead of 180 degrees.

A properly balanced 600 cc 1 cylinder can run perfectly smooth. And I've had a 6 cylinder Ford 4.0L and a GM 3.8L both running on 3 cylinders, and while they lacked power, they were smooth since it was every other cylinder in the firing order that was disabled.
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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 09-14-2010, 10:27 AM   #27 (permalink)
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Quote:
Originally Posted by saand View Post
Thanks edkiefer, good link explains balancing well. If others dont know if a 2 or 3 cylinder engine is "balanced" as described in the link in the last post by edkiefer it doesn't mean the engine will be free of vibration as other modes of vibration occur.

Well i tried out removing the injector signal to 1 and 2 injectors and it was an interesting ride. The car lugged a lot when accelerating up but if i was sitting at 70 kph it was drivable. I believe the lugging is because there is a dead spot in acceleration during a quarter of the cylinder cycle so less power therefore require higher revs to go to the next gear. My automatic car obviously didn't know this so every time it went up to the next gear it would lug. So i don't think i can go any further until i see if i can make a manumatic out of my auto.

In general besides the lugging it wasn't too bad i think when actually moving at speed i would barely notice the missing cylinder.

Not sure about vibration though which could compromise the life of engine parts.

So at this stage im going to look into changing my car to a manumatic and ill have to think about if i can deactivate a cylinder on the fly from the cabin. This would let me get up to highway speeds, deactivate a cylinder and reduce some fuel usage. The issue i have to think about is how to stop the pumping losses of the cylinder on the fly
If you want to disable half your engine, find out your firing order. On many 4 cylinders, it is 1-3-4-2. The outside cylinders are both at top dead center at the same time that the inside cylinders are at bottom dead center. Since you are going for economy, disable cylinders 1 and 4 and you should have a non stumbling engine.

I apologize I haven't read the whole thread, but one thing to watch for is if you are doing this to a fuel injected car, you need to consider what the o2 sensor is going to do when it detects 2x the o2 it should be seeing; ie it will detect a highly lean condition and the ECU will dump fuel in an attempt to correct it. There will be so much excess fuel in the 2 running cylinders it will wash past the piston rings into the crankcase and dilute the oil. I had a Explorer I did just that to; I disabled half the cylinders remotely from the drivers seat. But I noticed the oil level going up (it had a slow leak, so it was something I checked on regularly.) A little bit too late I realized the problem and the engine quit on me.

Don't think I believe it to be impossible, but either through electronically halving the signal from the o2 sensor or rerouting the exhaust, it will need to be dealt with if you value your engine.

Something else to consider, a 100 hp 4 cyl running on 2 cylinders will produce less than 50 hp at the crank due to the pumping losses from the 2 dead cylinders. My best guess would be about 35 hp but that's a shot in the dark sort of guess.
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Originally Posted by jamesqf View Post
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 09-14-2010, 10:27 AM   #28 (permalink)
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Harleys are a good example of how NOT to make an engine. I pulled up next to one at a stoplight and the handlebars, seat, trunk, everything was shaking like crazy. Good if you're a lady, I guess. I can't believe people still buy them.
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Old 09-14-2010, 11:26 AM   #29 (permalink)
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yes, Harley was bad example as it is made to vibrate and sound the way it is but it still will always be as you go up in cylinders the engine smooths out 1, 2, 4 ,6 ,8, 12 they generally get smoother . Most motorcycles that run smooth are 4 cylinders (Honda, Yamaha ,Suzuki )
Also the size of each cylinder has a affect , thats why large 4 cylinder have counter-balance shafts .
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Old 09-14-2010, 08:52 PM   #30 (permalink)
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Shadetreemech good to hear from someone that has tried to deactivate cylinders, I had not thought of the problem of excess fuel in the cylinders flowing past the piston rings. I will have to do something with the unused cylinder exhaust ports if/when i attempt this again.
Interesting to see you say there are 2 cylinder engines that can run smooth. Do you know what configuration that is in? a straight two, v twin or boxer twin (flat). I understand that a flat engine design can be perfectly balanced however if i was to convert my car into a 2 cylinder it would be a straight 2 and my initial concern was if it would be inherently unbalanced due to a pulsed firing order or from the 2 cylinders going in the same direction all the time and counter balances cant account for the piston movement up and down.
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 am still going to have to convert to a manumatic before i can progress with this cylinder deactivation mod anyway, the lugging was very unpleasant when testing.

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