Change your V-8 to a 4 banger

[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.