Change your V-8 to a 4 banger

[twhite]

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

[Johnny Mullet]

This was discussed here before, but I can't find the thread.

My conclusion is that under-powering an already heavy vehicle will actually cost more efficiency than save since they have to work harder.

[Tony Raine]

do you remember the 4-6-8? utter disaster.

plus, your running cylinders would be out of balance, and would have to lug around extra pistons. and don't forget spark and fuel delivery. its a cool idea, but would have to be electronically controlled, like the dodge "displacement on demand." otherwise you are driving around a big-underpowered truck that can't do what its designed for. might as well buy a car.



food for thought:
a few years ago, gm offered a $6000+ discount on 3/4 ton pickups ordered with the 4.3 v-6. heavy-duty chassis, but not enough power to use it. major failure. no i don't have any on-paper proof. my work buys odd no-option work trucks all the time. they passed that one up. (for example, we have a 93 dodge ram 3/4 ton dually with the small v-8 and independent front suspension, and a 2008 ford f-350 dually with the 5.4 v-8 )

[dann_04]

The 4-6-8 thing failed due to bad design. The new systems work well and improve the fuel economy. they do this by only shutting down the cylinders while at a steady low load, like cruising on the highway at a sustained speed. Honda has this with some of their v6's, Chevy has it on their new v6 impala(my friend has one), and dodge has it as well. There may be others, but those are the ones that come to mind. In my opinion, if you have to have the ability to tow a bajillion punds and have 300 horses, good for you, but it seems dumb to be cruisin on the highway to work in a behemoth doing 65mph and getting 14mpg when the little car next to you is doing the exact same thing and getting 30mpg. Why not only use the power when you need it? More companies should do this. Instead we have xfe versions of suvs now that get +1 mpg. Yeah, on big vehicles every mpg counts i know and its like a 7% increase, but why don't they just use their brains and design a variable displacement system so they gain 5 or 6 mpgs under no load and then have the powere when they need it? Sorry for my rant....I do that sometimes lol.

[Tony Raine]

this is a bandwagon i wish ford would jump on. my little 2 door suv, with a (properly contolled) "2-4-6" would be beyond awesome.

[mwpiper]

ditto with my Ford Escape. I'm cursed...CURSED mind you...with too much power.

I disagree that you have to seal the valves. If you just turn off the injectors, the cylinders would pump cold air. Pumping losses remain the same. It would not be as good as closing the valves, but better than status quo. The problem is whether or not pumping cold air will quench the catalytic converter. Both my V-6's fire alternatively front to back. So making them three cylinders involves killing the cylinders on the front bank. I have a scheme that would divert the exhausted cold air from the dead bank to a small muffler so the cat would only get fed from the hot cylinders.

Right now, I have a surplus car because my daughter is away at school. Who's going to be sacrificed?

[taco]

chevy does it by using push rods that turn and shorten.
u can see a big jump on the instant read off.

[RH77]

First welcome...

Next -- I tried this 3 years ago by running my 4-cyl as two, by switched injector deactivation. Forget it if you're running an oxygen sensor, it will not work. An engine swap would be easier...

RH77

[twhite]

hi Johnny,

You're right,under power in a heavy vehicle is not the way to go. I knew a guy that put a falcon engine in a school bus, he got horrible gas mileage. That said, most of the cars on the road today are totally overpowered. Any time you have a 400 plus engine in a half ton pickup your miles per gallon are going to be seriously compromised. so, what I'm trying to do is give the guy that's stuck with one of those pigs another option, at least until he can afford something smaller.

RH77, you've got my respect and admiration. it takes a lot of guts, for most people to even think about going from the V8 down to four, but from four to two , that's a big jump. It gets me thinking, my old Volvo has at least twice as much power as it really needs. hummmmmmmmmmmmm. I would probably have to grind off the cam lobes. If I decided I didn't like it, I'd have to buy a new camshaft, and then reset all of the valves. I guess that's why I'm reluctant to try it, I'd rather experiment on an old beater.

piper,I think it would be better to close off the valves. This is why, because you would still be compressing on the compression stroke, and sucking on the intake stroke.that would take a lot more energy than simply pumping the same air up-and-down. but, I think your car would be the perfect candidate for it.

Best wishes, Tom

[johnmyster]

Keeping the rotating assembly may make for a balanced motor in terms of rotational/oscillating mass. However, you'll never account for the fact that your power strokes will now become unevenly spaced.

Tell me this. Why can a smaller displacement motor generally create the same amount of power than a larger motor while doing so at higher efficiency? This is a comparison of a smaller motor and a larger one at the same power level.

It's because of pumping work. An engine is a pump. It's pumping air from intake manifold pressure to exhaust manifold pressure. Any time you pump from low pressure to high, you have to input energy. The difference is that the smaller engine, in order to keep up at a lower power level is running at higher manifold pressure. Therefore in terms of pumping work, gas engines are more efficient when they are working closer to their maximum volumetric capacity. So a 10L engine working at 10% throttle is less efficient than a 1 L engine working at 100% in terms of pumping work. This is one reason why it's more efficient to "shift early and use more throttle" in manual cars. Delta P is smaller.

This is one of the reasons for EGR. By introducing non-volitile air, you can cut back the fuel to air ratio, raising intake pressures at a given power output. Pumping work falls. Delta P is smaller.

This is one of the driving forces behind BMWs efforts to eliminate the throttle plate and use variable timing and duration intake valve actuators. They get to keep the intake manifold near zero vacuum and control the charging of the cylinders with the intake valve. No pumping losses because they are changing the charge volume rather than the charge pressure of the cylinder. Delta P is zero.

If you totally deactivate cylinders your motor is going to shake and wrattle like crazy. If you deactivate cylinders and still leave the valves active, you're going to put extra oxygen into the exhaust and cause the computer to dump extra fuel into the active cylinders - serving only to reduce economy, throw a MIL, and burn up the catalyst.

If you want to do this, remove the pistons and rods from the undesired cylinders. Redesign a new cam and crank around a rebalanced firing order. Reprogram the computer, and drive off into the sunset.

[twhite]

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..

A lot of the engines in the past ran with unbalanced power strokes. Harley Davidson and John Deere come to mind.

Best wishes, Tom .

[johnmyster]

I gave examples because I knew I wouldn't be believed. "Pumping work" is real. It's the reason you're advocating smaller engines that can do the job more efficiently. It's one of the reasons that other variables aside, larger engines are less efficient at a given power level.

I'm underscoring the underlying principle behind what you suggest. However, as cited, there are difficulties/impossibilities to simply disabling cylinders on modern engines that weren't designed to do so. On a carbureted engine with no 02 sensors (gm used sensors and computers with carbs for awhile) there's going to be more to it than pulling pushrods or unplugging injectors.

Yes, and Harley engines aren't exactly considered smooth running either.

[dcb]

I agree that piston removal and leaving the valves closed is the most efficient approach. I bet you could take an air cooled vw and delete the front left and right rear pistons and pushrods pretty easily. Might need to cut off the big ends of the con rods and use them as a spacer. The odd fire isn't a huge deal, many of my bikes (including my current one) have uneven firing spacing, big whup.

Or custom grind a cam and turn the 4 cylinder into a two cylinder with two cylinders of "boost", or a 1 cylinder with three cylinders of boost and have the deactivated cylinders pump air/fuel in to the remaining cylinder.

[mwpiper]

piper,I think it would be better to close off the valves. This is why, because you would still be compressing on the compression stroke, and sucking on the intake stroke.that would take a lot more energy than simply pumping the same air up-and-down. but, I think your car would be the perfect candidate for it.

It might be better, but I'm dealing (hypothetically) with an engine I've got. An engine change reduces utility and it would probably be cheaper to buy a different car. Where's the fun in that?

The compression stroke and power strokes would balance out minus entropy losses. The intake stroke is still the intake stroke. The exhaust stroke uses less power because there's less pressure and lower velocity through the exhaust valve.

Two solutions for the cat problem.
1) put a diverter valve on the exhaust pipe from the dead bank to a small muffler (to keep the car from sounding like an air compressor). Cat only sees hot exhaust from active cylinders.
2) allow the dead side to suck exhaust from the live side (EGR on steroids). The dead cylinders pass exhaust into the cat.

Instead of closing the valves which is mechanically very difficult, put on a dual intake header/plenum that has a cutoff valve to the switched bank. This is doable.

[dentprone]

Originally Posted by dcb

I agree that piston removal and leaving the valves closed is the most efficient approach. I bet you could take an air cooled vw and delete the front left and right rear pistons and pushrods pretty easily.

I'm off topic, but have you ever seen where they build air compressors from air cooled VW engines? Run the motor on just two cylinders and use the others to pump air? I'm sure there are plans somewhere online, saw the idea a few years back.

[extragoode]

This is a little off topic too, but for engine that already have the fuel cutoff it would be nice if there was a way to manually switch it to lower displacement. My mother in law has a GMC Yukon with the flex fuel engine that can switch from 8 to 4 cylinders, but she complains that it still gets horrible gas milage. So a couple weeks ago, I got the opportunity to drive it and was ready to see what I could do with it since I figured she was heavy footed with it. It NEVER switches unless the vehicle is COASTING. I used the cruise on flat ground all the way down to 45mph and it still never switched. Anything below 45 and the TC unlocked.

[RH77]

Originally Posted by extragoode

This is a little off topic too, but for engine that already have the fuel cutoff it would be nice if there was a way to manually switch it to lower displacement. My mother in law has a GMC Yukon with the flex fuel engine that can switch from 8 to 4 cylinders, but she complains that it still gets horrible gas milage. So a couple weeks ago, I got the opportunity to drive it and was ready to see what I could do with it since I figured she was heavy footed with it. It NEVER switches unless the vehicle is COASTING. I used the cruise on flat ground all the way down to 45mph and it still never switched. Anything below 45 and the TC unlocked.

I completely agree. I had a chance to drive Chevy Impalas / Montes with every engine option over the last 7 years -- this included the 3.9L V-6 "LZ8 and LZG", and the 5.3L V-8 "LS4 with AFM" (active fuel management or cylinder shutoff).

The LZG had the E85 option, which was noted to disengage cylinders more frequently with the additional power, but was very inefficient with the ethanol. With the standard AFM LZ8, it was tough getting 3-cylinder mode to engage (a dash-display showed when it happened + you could feel it). It helps in the city a little bit, but get out on the highway at 70 MPH with a headwind, and it does nothing. It was noted from the SG that 50% load was the basis for the algorithm.

The conclusion was that it did nothing but add weight and cost to the model:
3.9L----------: 24.3 MPG
3.9L with AFM: 24.9 MPG
5.3L with AFM: 22.0 MPG

On a side note, the 3.5L base without E-85 capability averaged 28.7 MPG. The E-85 capable engines have a larger fuel tank and a bit more overall power -- 26.4 MPG without E-85, 21.4 MPG with E85. ~E60 was 23.1 MPG

RH77

[Will]

It would be cool if they offered some kind of system like this after market. Though I don't think I would use it on my Metro.

[aerohead]

At 80-mph ( not uncommon and actually legal in parts of Texas ) the SAE discovered that any benefit of small displacement is virtually lost.At lower speeds,there was definitely a correlation between displacement and MPG,however as speed increased,that advantage disappeared.I believe Chrysler credits there current system with a 6% mpg improvement across the board.And I believe the 8-6-4 engine used Eaton valve"enablers",which were plagued with problems,and that engine program was dropped from production.Removing pushrods could effect the lubrication system and top end lubrication.

[Formula413]

Originally Posted by johnmyster

Keeping the rotating assembly may make for a balanced motor in terms of rotational/oscillating mass. However, you'll never account for the fact that your power strokes will now become unevenly spaced.

Tell me this. Why can a smaller displacement motor generally create the same amount of power than a larger motor while doing so at higher efficiency? This is a comparison of a smaller motor and a larger one at the same power level.

It's because of pumping work. An engine is a pump. It's pumping air from intake manifold pressure to exhaust manifold pressure. Any time you pump from low pressure to high, you have to input energy. The difference is that the smaller engine, in order to keep up at a lower power level is running at higher manifold pressure. Therefore in terms of pumping work, gas engines are more efficient when they are working closer to their maximum volumetric capacity. So a 10L engine working at 10% throttle is less efficient than a 1 L engine working at 100% in terms of pumping work. This is one reason why it's more efficient to "shift early and use more throttle" in manual cars. Delta P is smaller.

This is one of the reasons for EGR. By introducing non-volitile air, you can cut back the fuel to air ratio, raising intake pressures at a given power output. Pumping work falls. Delta P is smaller.

This is one of the driving forces behind BMWs efforts to eliminate the throttle plate and use variable timing and duration intake valve actuators. They get to keep the intake manifold near zero vacuum and control the charging of the cylinders with the intake valve. No pumping losses because they are changing the charge volume rather than the charge pressure of the cylinder. Delta P is zero.

If you totally deactivate cylinders your motor is going to shake and wrattle like crazy. If you deactivate cylinders and still leave the valves active, you're going to put extra oxygen into the exhaust and cause the computer to dump extra fuel into the active cylinders - serving only to reduce economy, throw a MIL, and burn up the catalyst.

If you want to do this, remove the pistons and rods from the undesired cylinders. Redesign a new cam and crank around a rebalanced firing order. Reprogram the computer, and drive off into the sunset.

Great post.

That BMW concept of essentially letting the intake valve serve as the throttle plate is fascinating, I had never heard of that before. I've learned all kinds of neat stuff on here.