Changing a V8 to a V4

If a smaller engine was an option for that vehicle you would be better off doing a swap to it.

The basic idea is actually okay, but like many things the devil is in the detail. You must "close off" those cylinders in some way. You cannot just take the pistons out since the crankcase oil would then go into the manifolds. You can actually leave the pistons in and find a way to hold the valves all open in those cylinders, then block off the manifold so that fuel does not get pumped through those cylinders. And which cylinders you disable makes a difference.

There ARE some cars on the market now that do disable cylinders under light throttle. I believe these are port injected engines so the valves are disabled and those injectors shut down.

eh, not really - you'd still have an out of balance 4-cylinder. Unless you disabled them in the proper order, and *left the pistons, con rods, etc.* in the bores. (e.g., you couldn't disable cylinders

1-3-5-7 like you'd think would make sense on a typical V-8 with a firing order 1-8-4-3-6-5-7-2, but you *could* disable 2,3,5, and 8 and it might not be too rough. Physically removing the pistons and con rods would likely make the engine physically unbalanced, and would also leave open oiling holes on the rod journals not to mention no way of controlling lateral movement of the big ends of the con rods on the same journals as the removed rods.)

AFAIK the real challenge in doing such a conversion would be retaining the valve lifters in their bores in the cylinders with the valves disabled - one would assume by removing the pushrods and rocker arms. If a lifter gets thrown from its bore, the engine will instantly lose most of its oil pressure, and that's bad.

Even if you work around this I'm not sure how much real gain you'd see

- you'd be removing the pumping losses from the disabled cylinders but you'd still have the frictional losses as you really can't remove most of the major mechanical components without serious modification, and it probably would be far easier simply to fabricate mounts to install a lighter, smaller engine without any missing parts.

nate

Forgot to mention - you'd want to have the valves held *closed* not open. Despite what you'd think, leaving a column of air in a cylinder is no biggie; it takes work to compress it, yes, but you get it all back on the downstroke (minus losses, of course.) Pumping losses are gone forever, however.

nate

No, no, no....you can't leve the valves open. If you do this multiple bad things will happen and you will makes the fuel economy worse becasue of pumping losses. If you want to deactivate four cylinders, you need to make sure both valves on those cylinders are CLOSED. With the valves closed, the air in a cylinder acts like a spring. This elimiates the pumping losses, and prevents blowing back stuff into the intake.

As for which cylinder to deactivate....take a look at what Chrysler and GM do with their engines that have "displacement on demand." These V-8 deactivate 2 or 4 cylinders in order to improve fuel economy.

Ed

When I was in college, I got to be friends with a mechanic who had a shop next door to where I lived. His son, a decent mechanic, was returning to town one night with his wife when he had a connecting rod problem with the old Dodge engine. He pulled off the road, jacked up the car, and dropped the pan. He removed the piston totally, jammed a rag up in the cylinder bore, and buttoned her up. He drove back home with no other modifications and made it just fine. This was a trip of some 60-70 miles.

I would not have thought it possible, but it happened.

Probably wouldn't work for a modern engine, particularly a V-8. With a connecting rod missing on a V-8, the other rod on that journal would not be properly located and the oil flow path would be screwed up.

Ed

I saw this done with a straight 6 many years ago, by removing the (solid) lifters. (Someone else mentioned the problems you'd run into doing it with hydraulic lifters.) I drove or rode in the car for a couple thousand miles in this condition, on a long trip. Running on 3 cylinders didn't change the gas mileage, it just reduced the power.

e6

I'm skeptical as well; the lack of endplay control might not be a problem if, say, it were a seven main bearing six cylinder but I can't see how you'd keep from losing all oil pressure without plugging the hole in the crankshaft somehow.

Of course, you may have been omitting a step like "he wiped down the crank with Brakleen and taped over the journal with a couple turns of metal duct tape" but the whole concept of the "repair" still makes me a little queasy :)

nate

nate

Did me too. But it happened.. That would have been in about 1964, and the Dodge would obviously have been several years older to have a con rod problem. I cannot see why he didnt essentially lose all oil pressure when he removed the con rod big end. Or, maybe he did.

Maybe you can limp a long way with severely reduced oil pressure. A one way trip for that engine, Im sure.

The issue is not solid vs. hydraulic (although hyd. lifters are

*always* pressure fed, so it's good to think about) it's whether the lifters get positive, pressurized lubrication from the engine's oiling system. e.g. old Studebaker V-8s used solid lifters but also had oiling holes in the lifter bores, so that would not be a good engine to try to run with a pair of lifters removed.

nate

The old Volvo B-18/B-20 had dry solid lifters. The valve train was lubricated through an oiling hole through the cylinder head that ended up in one of the rocker shaft pedestals.

I have two uncles who did this as a stopgap measure to get home on two different vehicles. IIRC, both were straight 6's (one was an old GMC bus and the other was a Dodge car probably a /6.) They both made it a couple hundred miles, but it was apparently pretty ugly a drive. The engine needed a total overhaul anyway, in both cases they were probably

200,000 mile motors, so no concerns about long term damage, just didn't want to be stuck in Saskatchewan...

Ray

"Steve W." wrote in news:ftlsc5$6fk$ snipped-for-privacy@aioe.org:

Believe it or not, Cadillac's V-8-6-4 of 1981 operated by holding the unused cylinder's valves closed at all times.

Apparently there was no significant loss in efficiency from having the valves closed, but plenty of gain from reduced pumping losses.

See the column "Mechanical Marvels" in the April 2008 issue of "Hemming's Classic Car" magazine. This article features the V-8-6-4.

In 1981 I drove a new V-8-6-4 Seville on several occasions. Cylinder deactivation/activation was imperceptible, and it was fun to watch the dash readout show the change in the number of activated cylinders. When new and in correct adjustment, Cadillac's system worked very well.

Right. That was my bad on valves being open. As you said, they should be closed.

BTW, midget race cars have been powered for years by four cylinder engines made from V-8s. Most cut off one whole bank, but there have been a few that were cut athwartwise to create a V-4. Of course, the cranks were cut too. Don't know how well the balance was, but the things sure are powerful. There have been Chevs, Fords and Mopar engines treated this way. These are available in the market but they are FAR too expensive to use as an economy measure, though they do run on pure methanol. Lately I have been paying a lot less for methanol than gasoline, but of course the fuel consumption is twice what it is for gas, so it really is more expensive, even without the taxes.

It's not so much that you need to remove the lifters, it's that if they're loose in their bores, they might get smacked out of the lifter bore by the cam and then the engine would lose pressure.

nate

Why would you remove the lifters? Removing the pushrods will not cause any problems in many engines. I did that to a chevy V8 40 years ago. It had a bad cam lobe so I disconected the 4 cylinders that were fed by the same barrel of the 2 barrel carb. As a 4 cylinder it ran and sounded like a tractor - slow acceleration but very steady sounded pretty good if you like that sound. It definitely did get better gas mileage since the bad cam was pretty much nullifying that half of the engine anyway. But gas was cheap and this was a station wagon so it was only run like that for a couple hundred miles until a good CAM was located.

-jim

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The Cadillac system rarely worked well, and the real world gains in fuel economy never matched the claimed improvement (ditto for the current displacement on design systems from GM and Chrysler). Works good in the very predictable EPA tests, not so good in the real world (at least for some people). The only theoretical gain is from a reduction in pumping losses (not all that high at part throttle) and a slight improvement in thermal efficiency because the working cylinders are more fully charged. If / when individually controlled electrically operated valves become a real world everyday item, cylinder deactivation should be cheap, reliable, and effective. Current system are .....

Ed

If you want four four cylinders, instead of eight cylinders in that vehicle.Put a factory manufactured four cylinder engine in there. cuhulin