how to change your V8 to a 4-cylinder - Page 2 - Fuelly Forums

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Old 08-21-2008, 07:55 AM   #11
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By deactivating the exhaust valve first, this allows the capture of a burnt air/fuel charge or exhaust gas charge in the combustion chamber. The capture of exhaust gases in the combustion chamber will contribute to a reduction in oil consumption, noise and vibration levels, and exhaust emissions when operating in V4 mode cylinder deactivation mode.

During the transition from V8 to V4 mode, the fuel injectors will be turned OFF on the deactivated cylinders. To help prevent spark plug fouling, the ignition system secondary voltage or spark is still present across the spark plug electrodes on the deactivated cylinders. If all enabling conditions are met and maintained for cylinder deactivation operation, the ECM calibrations will limit cylinder deactivation to a cycle time of 10 minutes in V4 mode, then return to V8 mode for 1 minute.
See that line about oil consumption? They're making sure to keep enough air in there to maintain compression, which keeps oil out of the chamber.

Without sufficient pressure oil leaks past the ring (some does anyways, just in small amounts) and in an engine you just pull the pushrods out of, those chambers will be filled with oil in little time, creating even MORE paracitic loss.

If you try to block off the oil feeding that piston, then it can run dry and very quickly actually WELD the rings to the cylinder wall.

Even GM won't run the system on the engine constantly, and I'm betting it's because they know that the pressure in the cylinder will eventually seep out, and they need to restore the compression in those cylinders to keep the oil under control.

And for engines that are older, were tollerances weren't as tight and they have more piston to wall clearence, there's going to be even greater issues with oil leakage.
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Old 08-21-2008, 11:41 AM   #12
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Gollum, .

I do see that line about the oil consumption.that's something that would concern me greatly if I were trying to design an engine that could disable the cylinders on demand. But we're not talking about that, we're talking about something that the backyard mechanic can do to an overpowered rig. So yes,you are going to get a little oil seeping past the rings. Whoopie-do. So, if you ever put the push rods back in, you will wind up burning about half a teaspoon of oil. and no, the cylinder will not fill up with oil. If it even started to, the increased compression would push it back down past the rings.

Lug nuts comments deserve a closer look. Just as a thought experiment lets carry it to the ridiculous, and work our way backward into sanity. We could put an a V 16 into a Honda Civic, but we wouldn't expect anything like good gas mileage. The truth is, all in engines have to have a certain air to fuel ratio in order to even run. Part of the energy in your mixture is doing nothing more than igniting the other part. that's the part that gets wasted. So, while you're idling along, your carburetor is giving you as lean a mixture as you can possibly burn. but you still have to have 302 in.? every other revolution, no matter how much power you're producing. at an idle, you are using only enough to keep the engine turning over. Every engine has a "sweet spot" or it's delivering the most eficiency that it can. that spot is usually about half throttle to three-quarter throttle.

What I'm trying to do here, is to give someone a really low cost option to squeeze some better gas mileage out of the car or truck that they already have.

Best wishes, Tom
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Old 08-21-2008, 11:54 AM   #13
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I'm simply trying to make sure you understand the risks you're inviting others to take, that's all. Not all engines will handle it the same.

I AM interested to see some before/after results from various setups though.
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Old 08-21-2008, 02:47 PM   #14
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Gollum, .



What I'm trying to do here, is to give someone a really low cost option to squeeze some better gas mileage out of the car or truck that they already have.

Best wishes, Tom
I think you might be doing trying to save someone money in theory, but you do not know if it would really work in an unknown application, how long it would work for in an unknown application, and you have not done it yourself in any application. I think it could be an interesting experiment, and from the bit of reading I did on-line it is far from as "simple" as you suggest. If some one reading this thread is there is considering following Tom's advice, i would suggest you do not unless you are willing and able to embark on a potentially high time/cost experiment. You could end up with a car that runs horribly or not at all and spend lots of time and potentially lots money un-doing the work. Tom, do your own experiments and tell us how it goes! I would be very interested to see the results.
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Old 08-21-2008, 06:38 PM   #15
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I think you need to go back and reread my post. I've got five years experience driving a truck with one of the cylinders disabled. That cylinder was disabled in exactly the same way that I'm suggesting.

so, how is this a high cost/ time experiment? I'm figuring under 20 bucks for a valve cover gasket set, and about 15 minutes to do the work. and another 15 minutes to undo it if you don't like what you've done..

And no, I can't tell you how it will work on your particular vehicle. what I can tell you is this: that it's not going to mess things up permanently.

best wishes, Tom
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Old 08-21-2008, 10:48 PM   #16
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I think you need to go back and reread my post. I've got five years experience driving a truck with one of the cylinders disabled. That cylinder was disabled in exactly the same way that I'm suggesting.

so, how is this a high cost/ time experiment? I'm figuring under 20 bucks for a valve cover gasket set, and about 15 minutes to do the work. and another 15 minutes to undo it if you don't like what you've done..

And no, I can't tell you how it will work on your particular vehicle. what I can tell you is this: that it's not going to mess things up permanently.

best wishes, Tom
you said the v6 had been disabled by some else. so you have no before and after data points and you did not do the disabling yourself. what did i miss? those gmc v6's were low revving, low compression, low horspower, analog spark, caburetted truck motors. they have very little to do with to days high compression, high revving, fuel injected computer/sensor, managed motors which includes v8s. you have a theory that you are suggesting "poor folks" take the risks on to "save money". how? what evidence? you have presented nothing. the late gm and current honda cylinder management setups are engineered solutions that are warrantied. to suggest this is a 15 minute project is silly. maybe on a 49 chevy v6 but i doubt that too. frankly you are giving bad advice. if you want to do it, great, I think it is a wonderful project idea and i look forward to your results.
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Old 08-22-2008, 04:36 AM   #17
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I don't even think that was a V6, I think those trucks came with a straight 6. Anyway when disconnecting the valves to deactivate a cylinder you also have to block fuel from going into the cylinder. That is why you can't just disable 1 or 2 cylinders. On a V6 you disable 3, on a V8 you disable 4. You have to take the intake manifold off and block off the fuel going to that side of the engine I bet on the 49 Chevy the deactivated cylinder was still getting fuel dumped into it, but not getting burned.

I agree that the notion of a "poor" person doing this is not a good recommendation. Poor people usually do not have the luxury of having a spare vehicle, so they will be doing this to their only vehicle. If something goes wrong they will be without transportation. If something seriously goes wrong then this poor person is now looking at the prospect of having to purchase another vehicle. This might be fun for me to play with on my 86 Chevy p/u or my 81 Buick, but I have 3 vehicles. If one breaks I still have other vehicles to drive.

A poor person's better option is to sell the v-6 or v-8 vehicle and purchase an 80's era Ford Escort wagon, preferably with a 5 speed. I looked on Kelly Blue Book's site and an 88 Escort wagon 5 speed, 120,000 miles in fair condition should sell for $450, Good $680, and Excellent $805. This is certainly more preferable than risking the engine in your only vehicle, and gets you far better mileage than the cylinder deactivation would net you.

-Jay
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Old 08-22-2008, 07:25 AM   #18
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Something else to note, it's best to do this kind of thing by making sure the valves aren't even opening, and removing the pushrods work... on a pushrod engine.

Removing tappets, or rockers from an OHC engine will be a bit more involved and will vary from engine to engine depending on the head design. And almost all engines are OHC now days. GM's LS engines are in a very small minority of pushrod engines left.
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Old 08-22-2008, 07:45 AM   #19
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I don't even think that was a V6, I think those trucks came with a straight 6. Anyway when disconnecting the valves to deactivate a cylinder you also have to block fuel from going into the cylinder. That is why you can't just disable 1 or 2 cylinders. On a V6 you disable 3, on a V8 you disable 4. You have to take the intake manifold off and block off the fuel going to that side of the engine I bet on the 49 Chevy the deactivated cylinder was still getting fuel dumped into it, but not getting burned.

I agree that the notion of a "poor" person doing this is not a good recommendation. Poor people usually do not have the luxury of having a spare vehicle, so they will be doing this to their only vehicle. If something goes wrong they will be without transportation. If something seriously goes wrong then this poor person is now looking at the prospect of having to purchase another vehicle. This might be fun for me to play with on my 86 Chevy p/u or my 81 Buick, but I have 3 vehicles. If one breaks I still have other vehicles to drive.

A poor person's better option is to sell the v-6 or v-8 vehicle and purchase an 80's era Ford Escort wagon, preferably with a 5 speed. I looked on Kelly Blue Book's site and an 88 Escort wagon 5 speed, 120,000 miles in fair condition should sell for $450, Good $680, and Excellent $805. This is certainly more preferable than risking the engine in your only vehicle, and gets you far better mileage than the cylinder deactivation would net you.

-Jay
Good stuff. Here is a link to the motor I thought Tom was talking about. I dont know why i thought Tom was talking about a v-6 because on re-reading the post it is never mentioned. It was in an 63-65 gmc 1 ton pickup I was around when I lived in Big Bear. myself and other neighborhood gearheads thought it was pretty neat, it made a very unusual sound. .

http://en.wikipedia.org/wiki/GMC_V6_engine
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Old 08-22-2008, 08:00 AM   #20
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The article I had read a while ago described fixing the intake valves shut, and removing the exhaust valves. Shutting all valves will result in a parasitic cycle of pressure/vacuum on the deactivated cylinders. This allows the deactivated cylinders' pistons to just "bounce" up and down on air.

-Jay
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