how to change your V8 to a 4-cylinder
or you could change your six-cylinder into a four-cylinder, or a three cylinder. Or if you're not feeling so courageous, you can change your V8 into a six-cylinder.
this isn't exactly a new idea, but a quick look at the board I didn't see it listed. It would be really nice if you could yank that biggie engine out, and saw off half of the cylinders. But that would be a heck of a lot of work, and I'm inclined to believe that without four of the Pistons you would have a major inbalance problem. So the answer is simply this: INACTIVATE THEM. Doing this is simplicity itself, and on most of your V. eights, readily reversible if you don't like what you've done. Simply pull the valve covers, and remove the push rods. If you have a fuel injection, you will also want to pull the wire's at the fuel injectors. I told you this isn't a new idea. Cadillac used it back in the 80s. They called it 4- 6 - 8 . Honda uses it now, they call it "active cylinder management" of course those guys all use computer control, but what we're doing we could call "inactive cylinder control" At this stage of my life, both of my vehicles have four-cylinder engines, and I'm not quite ready to rob them. I would have to grind the camshaft lobes, since they're both overhead cams. I would want someone else to make that experiment. Best wishes, Tom |
There's people talking about it, and one guy with a 6 cylinder pickup here tried it recently - the engine did not run all that well and he ended up reversing it.
GM not only did it on the 4-6-8 engine in the early 80's, but also on the early NorthStar V-8's. They now sell new cars that do this - Its called Active Fuel Management. From what I hear the current version they have works quite well. -Jay |
.hi Jay,
the North Star engine was what I was really thinking about. I'm not a big Cadillacs fan, so I don't really know how well they worked. So obviously this idea would work better for someone who lived in Nebraska or Oklahoma, than for someone who lives in Colorado. I live in Oregon, which is pretty mountainous. so, while I suggested it to several people here, no one has taken my suggestion seriously. This is kind of academic for me, but I thought I would throw the idea out anyway. I work at home, and don't really go anywhere.but I know a lot of poor folks that got stuck with those big V8s. that seems to be the way that things work, the people that need to save gas (and money) are the ones that have to wind up spending the most of it. Best wishes, Tom |
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Here's my suggestion. Correct me if I have some bad assumptions
I think rather than disabling cylinders it would be better to turn the engine into an eight stroke engine with the extra strokes disabled. Put a double sized, as in 2X the number of teeth, gear on the end of the cam, this is for OHCs. Grind a custom cam that has skinnier lobes spaced correctly. Skinnier lobes because as the cam is spinning half speed the valves would stay open twice as long. This way the motor would still have the correct firing order for balance. If the firing order was 1-4-2-3 it would still be the same but would be compress 1 fire 1, compress 4 fire 4, compress 2 fire 2, compress 3 fire 3 for one rotation of the cam. I don't think doing much else would be needed as the distributor turns with the cam and thus the ecu would think you were running at 1/2 the rpms and would pulse the injectors, fire the plugs, at the correct points. With some VTEC type tricks you might be able to make it switch between the 2 modes by only running 8 valves at a time in a 16 valve motor and have DOHC with one spinning the normal speed and the other half speed. |
It's a neat idea, but cadillac had huge problems with it back with the 4-6-8.
It's not as simple as telling valves not to open, or telling ignition not to spark. Cutting out cylinders causes a severe balance change and puts more stress on the crankshaft and block itself. Firing orders are designed to do thier best to counter act eachother, otherwise you'd see a 4 cylinder fire from front to back, not staggered. There's many other issues involved, but basically it comes down to the fact that the modern engines that cut cylinders out alternate which cylinders they are. This fixes most of the previous issues. The other thing is that these engines have modified oiling systems so that each cylinder still recieves the correct lubrication when not firing. It's easy to over oil, or starve a piston that isn't creating any cylinder pressure. I think it's a good idea though, and it'd be interesting to see what hot rodders could do with the idea. If I tried it I'd try to write some code for megasquirt running EDIS to not fire each cylinder every other cycle. |
well, as far as compressing air goes, it really doesn't do that. because each cylinder is totally closed, what happens instead is that each piston alternates between compression and vacuum. There is bound to be some losses associated with that. But those losses aren't nearly as bad as you might think.
as far as creating an imbalance in the engine,it's up to you to decide whether you can live with it. Many years ago, I was fortunate enough to own a 1949 Chevy pickup truck with a five cylinder engine. It was really a six cylinder. Anyway, I had the old thing for about a couple of years, and never noticed anything really different about it. But for some reason I decided to do the old spark plugs test. You know, the one where you pulled the plug wires one at a time. Anyway, I noticed that the fifth cylinder didn't seem to be firing. After some more testing, I pulled the valve cover, and saw that someone had taken the push rods out. So I went down to the salvage yard, got another couple of push rods. When I put them back in, the engine ran terrible, it was backfiring through the carburetor. What had happened was: the exhaust lobe of the cam had been ground off, so someone before me and simply taken the easy way out, and pulled the push rods. So, I simply pulled them back out again, and drove it for another couple or three years until it finally went to standard iron. I don't remember why it died, but he didn't have anything to do with the fifth cylinder. that 8 stroke idea sounds intriguing, but way more complicated than I wanted to deal with in this thread. As far as starving a piston for oil, I don't see how that could happen at all. It's receiving oil at the same pressure, and the same splash as all the rest of them. What will probably happen, is that oil will migrate past the rings. That's a good thing though, the only trouble it could possibly create is that it could possibly smoke a little if you reconnected the cylinder. Remember, air compressors oil the same way,and they typically last for decades if not centuries. Best wishes, Tom |
There has been a lot of discussion of the idea of DIY displacement-on-demand. Do a little bit of searching. Here's one: https://www.gassavers.org/showthread.php?t=7132
As mentioned by Jay, GM's doing it with what they now call "Active Fuel Management". They close the valves, disable fuel injection for those cylinders, and turn off ignition for them. It works well, though the result tends to be only a moderate improvement. |
Ok, more on this...
https://www.camaro5.com/forums/showpo...4&postcount=46 Quote:
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V8 to V4? Big deal! I turned my 3.5 liter V-6 Honda Odyssey into a bicycle. Bye-bye Pre-quel!
The only advantage to this practice of cylinder de-activation is obtained by increasing the efficiency of the remaining operational cylinders by enough to offset the parasitic drag of toting around the dead ones. Driving at x speed requires y power. Whether y power is produced by 4 or 8 cylinders doesn't change the amount needed to maintain that speed. The fuel savings comes from the amount of fuel needed to produce y power from 8 cylinders versus y power from 4. The four have to produce twice as much each as if there were 8 contributing. The load on each of four is twice as much as as on each when 8 are working, but the amount of fuel needed may be slightly less than twice. The increase in the efficiency of converting fuel into power is sometimes enough to make up for the four sets of rings scraping up and down, the bigger radiator needed for when all 8 are working, the bigger water pump needed for 8, the bigger alternator needed to top-off the bigger battery needed for the bigger starter motor. It's still more fuel efficient to increase the displacement of a smaller engine by forced induction (turbo or supercharging) than to drop a large displacement engine to the smaller capacity. |
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