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

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Old 08-20-2008, 01:01 PM   #1
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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
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Old 08-20-2008, 01:15 PM   #2
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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
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Old 08-20-2008, 01:33 PM   #3
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.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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Old 08-20-2008, 01:43 PM   #4
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Quote:
Originally Posted by twhite View Post
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
I'll give your proposal consideration. hmmmm. is the motor still compressing air in the "deactivated" cylinders? if you remove the push rods would the valves will be closed all the time? It would seem, so you would be compressing air on every stroke for no reason i can think of. Is it hard to compress air, in terms of energy use? I think it is. this experiment might not work. but it does seem really simple.
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Old 08-20-2008, 02:13 PM   #5
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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.
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Old 08-20-2008, 02:24 PM   #6
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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.
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Old 08-20-2008, 03:07 PM   #7
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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
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Old 08-20-2008, 04:50 PM   #8
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There has been a lot of discussion of the idea of DIY displacement-on-demand. Do a little bit of searching. Here's one: http://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.
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Old 08-20-2008, 04:53 PM   #9
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Ok, more on this...
http://www.camaro5.com/forums/showpo...4&postcount=46
Quote:
Here is the complete AFM/DOD description straight from the gm service manual:

To provide maximum fuel economy under light load driving conditions, the engine control module (ECM) will command the cylinder deactivation system ON to deactivate engine cylinders 1, 7, 6, and 4, switching to a V4 mode. The engine will operate on 8 cylinders or V8 mode, during engine starting, engine idling, and medium to heavy throttle applications.

When cylinder deactivation is commanded, the ECM will determine what cylinder is firing, and begin deactivation on the next closest deactivated cylinder in firing order sequence. For example, if cylinder number 1 is on its combustion event when cylinder deactivation is commanded ON, the next cylinder in the firing order sequence that can be deactivated is cylinder number 7. If cylinder number 5 is on its combustion event when cylinder deactivation is commanded ON, the next cylinder in the firing order sequence that can be deactivated is cylinder number 4.

Cylinder deactivation is accomplished by not allowing the intake and exhaust valves to open on the selected cylinders by using special valve lifters. The deactivation lifters contain spring loaded locking pins that connect the internal pin housing of the lifter to the outer housing.

The pin housing contains the lifter plunger and pushrod seat which interfaces with the pushrod. The outer housing contacts the camshaft lobe through a roller. During V8 mode, when all cylinders are active, the locking pins are pushed outward by spring force, locking the pin housing and outer housing together causing the lifter to function as a normal lifter. When cylinder deactivation is commanded ON, the locking pins are pushed inward with engine oil pressure directed from the valve lifter oil manifold (VLOM) assembly solenoids. When the lifter pin housing is unlocked from the outer housing, the pin housing will remain stationary, while the outer housing will move with the profile of the camshaft lobe, which results in the valve remaining closed. One VLOM solenoid controls both the intake and exhaust valves for each deactivating cylinder. There are 2 distinct oil passages going to each cylinder deactivation lifter bore, one for the hydraulic lash-adjusting feature of the lifter, and one for controlling the locking pins used for cylinder deactivation.

Although both intake and exhaust valve lifters are controlled by the same solenoid in the VLOM, the intake and exhaust valves do not become deactivated at the same time. Cylinder deactivation is timed so that the cylinder is on an intake event. During an intake event, the intake CAM lobe is pushing the valve lifter upwards to open the intake valve against the force of the valve spring. The force exerted by the valve spring is acting on the side of the lifter locking pins, preventing them from moving until the intake valve has closed. When the intake valve lifter reaches the base circle of the camshaft lobe, the valve spring force is reduced, allowing the locking pins to move, deactivating the intake valve. However, when cylinder deactivation is commanded ON, the exhaust valve for the deactivated cylinder is in the closed position, allowing the locking pins on the valve lifter to move immediately, and deactivate the exhaust valve.

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.

Switching between V8 and V4 modes is accomplished in less than 250 milliseconds, making the transitions seamless and transparent to the vehicle operator. The 250 milliseconds includes the time for the ECM to sequence the transitions, the response time for the VLOM solenoids to energize, and the time for the valve lifters to deactivate, all within 2 revolutions of the engine crankshaft.

Valve Lifter Oil Manifold (VLOM) Assembly
The cylinder deactivation system uses an electro-hydraulic actuator device called the valve lifter oil manifold (VLOM) assembly. The VLOM is bolted to the top of the engine valley, below the intake manifold assembly. The VLOM consists of 4 electrically operated normally closed solenoids. Each solenoid controls the application of engine oil pressure to the intake and exhaust valve lifters on the cylinders selected to deactivate. Engine oil pressure is routed to the VLOM assembly from an internal oil passage on the rear of the cylinder block.

All 4 VLOM solenoids are connected in parallel to a fused ignition 1 voltage circuit, supplied by the powertrain relay. The ground or control circuit for each solenoid is connected to a low side driver internal to the engine control module (ECM).

When all enabling conditions are met for cylinder deactivation, the ECM will ground each solenoid control circuit in firing order sequence, allowing current to flow through the solenoid windings. With the coil windings energized, the solenoid valve opens, redirecting engine oil pressure through the VLOM into 8 separate vertical passages in the engine lifter valley. The 8 vertical passages, 2 per cylinder, are connected to the valve lifter bores of the cylinders to be deactivated. When vehicle operating conditions require a return to V8 mode, the ECM will turn OFF the control circuit for the solenoids, allowing the solenoid valves to close. With the solenoid valves closed, engine oil pressure in the control ports is exhausted through the body of the solenoids into the engine block lifter valley. The housing of the VLOM incorporates several bleeds in the oil passages to purge any air trapped in the VLOM or engine block.

To help control contamination to the hydraulic circuits, a small replaceable oil screen is located in the VLOM oil inlet passage, below the oil pressure sensor. The oil pressure sensor is a 3-wire sensor which provides oil pressure information to the ECM.

During service, use extreme care in keeping the VLOM assembly free of any contamination or foreign material.

Cylinder deactivation may be inhibited for many reasons, including the following:

• Engine coolant temperature out of range for cylinder activation

• Engine vacuum out of range

• Brake booster vacuum out of range

• Transmission gear incorrect or shift in progress

• Accelerator pedal out of range or rate of pedal application too fast

• Engine oil pressure and temperature out of range

• Engine speed out of range

• Vehicle speed out of range

• Minimum time in V8 mode not met

• Maximum V4 mode time exceeded

• Decel fuel cutoff active

• Reduced engine power active

• Torque management active

• Catalytic converter over temperature protection active

• Piston protection active, knock detected

• Cylinder deactivation solenoid driver circuit faults
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Old 08-21-2008, 07:27 AM   #10
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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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