3 cyl. vs 4 cyl.

[balper]

There is a discussion going on in my neck of the woods regarding the efficiency of engine with 3 cylinders. Is it true that 4 cylinder engines perform better, are easier to maintain, etc... or is it just an "urban legend"?
My 60 HP has a 3 cylinder PERKINS engine, and I feel kind of strange when people start to talk about the "altogether superior" 4 cylinder engines

[Opti-Mist]

I'd say just legend. If there were a significant difference you would see it reflected in the marketplace. If 3-cylinder engines incurred greater maintenance costs the resale price would reflect it.

[john_bud]

Originally Posted by balper

There is a discussion going on in my neck of the woods regarding the efficiency of engine with 3 cylinders. Is it true that 4 cylinder engines perform better, are easier to maintain, etc... or is it just an "urban legend"?
My 60 HP has a 3 cylinder PERKINS engine, and I feel kind of strange when people start to talk about the "altogether superior" 4 cylinder engines

Welcome to the TBN community!

First off, you do know the difference between a 3cyl and a 4 cyl, right?

One has an additional cylinder.

That's about it.



Now for the subtle details. Let's make an assumption that there are 2 engines that each have 200 cubic inches of displacement (3.3 liter). They will both have about the same Hp. Let's give them the same diameter cylinders. The 3 cylinder will have a longer stroke. If the cylinder diameter is 4 inches, the strokes will be 4 inches for the 4 cyl and 5.3 inches for the 3 cylinder. Operational effeciency and low speed torque are typically greater with a longer stroke as there is more time at the top of the stroke with the combustion pressure the highest. More chemical energy is turned into mechanical energy. This means more torque to the wheels for the 3 cylinder across all RPM's. Score one for the 3 cyl!

The 3 cylinder will also have less friction. It has 1 fewer set of piston rings to drag up and down the cylinder, 1 fewer set of wrist pin, rod and main bearings. It also has 1 fewer set of lifters, pushrods, cam lobes, rocker arms and valves to operate. Less friction is less wasted energy and less fuel used for the same power output. Score one more for the 3 cylinder. As the failure rate of engine parts is pretty constant (a rocker arm will fail every 30 billion actuations for example) across all engine types, fewer parts means fewer parts that can fail. That means longer times between failures.

If the engines have the same size oil pumps, the 3 cylinder will have more oil flow on each bearing surface (because it has fewer bearings to share the oil). That should make the friction surfaces run cooler and wear at a lower rate making the 3 cylinder even more reliable.



So, if you want an engine that has more torque to pull a plow, uses less fuel and is more reliable --> get the 3 cylinder.


So why are there 4 cylinder engines? You can get more displacement from more cylinders and that makes more power. At some point, the benefits of 3 vs 4 (or more) change where the stroke gets too long to be practical or the rotating parts get to heavy etc. About the biggest 3 cyl's made are in the 200 cu inch range (3.3 L)

Hope this helps you with your 4 cylinder buddies! Personally, I think they are just envious of your long stroke.

jb

[mark4Jesus]

I used to have a 24hp Kubota with a 4 cyl. engine. The Kubota dealer told me that the 4 cyl. had more torque. Kubota went to a 3 cyl. engine at this HP and customers complained that the tractors did not have as much power. May be true for smaller engines, not the large tractors like yours.

[Egon]

There is no answer as there are just too many design considerations to account for.

The only definite the more cylinders the more power pulses the better the chances of smoother operation depending on cylinder configuration.

[Farmwithjunk]

Originally Posted by balper

There is a discussion going on in my neck of the woods regarding the efficiency of engine with 3 cylinders. Is it true that 4 cylinder engines perform better, are easier to maintain, etc... or is it just an "urban legend"?
My 60 HP has a 3 cylinder PERKINS engine, and I feel kind of strange when people start to talk about the "altogether superior" 4 cylinder engines

There is no "across the board" answer to that.

I'd match the performance of a 3-cylinder Perkins diesel against ANY comparable sized 4-cylinder engine on the market.

As far as torque.... The number of cylinders has little, if ANYTHING to do with that. Generally speaking, if you take 2 engines of the same displacement, one being a 3 banger and the other being 4, the 3 cylinder will USUALLY out lug the 4 banger.... Reason? Most likely, the 3 cylinder will have to be a longer stroke engine. (as well as bigger bore most likely) THERE is where torque usually comes from.

If a salesman told me that, I'd discount EVERYTHING he told me from that point forward.

Back in the early 60's Ford produced 3000's and 4000's with 4 cylinder engines. By the late 60's, they made the switch to 3 cylinder engines. Without any question, the 3 cylinder versions would work circles around the earlier models.

[Soundguy]

Originally Posted by john_bud

If the engines have the same size oil pumps, the 3 cylinder will have more oil flow on each bearing surface (because it has fewer bearings to share the oil). That should make the friction surfaces run cooler and wear at a lower rate making the 3 cylinder even more reliable.
jb

Hmm.. this discounts any functioning of the oil relief system.

For instance.. assuming similar engine technology used on this theoretical 3 cyl and 4 cyl engine.. we can assume simialr bearing clearances and oil passageways. If the same oil pump is used ( maybe same flow.. maybee not.. lets assume same flow ).. then I doub't there will be more unit oil available to each journal, if the bearing clearances are similar.. you can only push so much oil down an oil passageway. I would guess that the oil relief system would simply be bypassing more oil at the relief valve than the 4 cyl.. assuming both were operating at an efficience level where there was excess oil pressure generated at the pump than needed, and thus the excess was dumped ( an ideal system that has been in place for a long time ).

That's not a negative.. just an observation and a theory...one that doesn't amount to much.. except that i would not chalk 'superior lubrication' up as an automatic advantage for a 3cyl.. etc..

My onlt other though on that similar hp engine comparison would be a reverse corolary to the less parts/less friction, and that would be that the stress would also be spread over less parts. Thus.. if you are making 100 hp on a 3cyl eng.. and 100 hp on a 4 cyl engine.. then each part in the 3 cyl engine is under more stress. I.e. say if you divided by cyl number.. thus each cyl in a 4cyl would be bearing 25% of the 'work'.. whereas on a 3cyl.. each one is bearing 33.3% of the work.. etc.

In the end.. i think the firction losses benefits are more important than unit load.. thus still making a case for the 3 cyl.

In the early 60's ford discarded the 4cyl engines fo rthe 3 cyl engines. it was seen as a definate step up in reliability.. etc.

Only other negative i can see might be in 'smoothness'. I believe a 4cyl may sound smoother than a 3, and a 3 smoother than a deuce, and a deuce smoother than a 1 lung.

Anyone who has been around hit-n-miss engines and johnny poppers can attest to that. Over in the yanmar sub, it's recognized that the 3cyl versions exhibit much less 'yammer-hammer' than their venerable 2 cyl counterparts.

To the original poster.. IMHO.. given equal CID engines.. i don't see much problem in a 3 cyl vs a 4 cyl.

One other point. now.. if you take a 3cyl of less CID.. and jimmy it up to make the same hp of a larger 4cyl.. then.. I think you may run into a problem.

For example.. i'd choose a 4cyl NH 1920 vs a NH TC 30/33 any day of the week. Compairable hp machines.. except the 1920 has 1 more cyl.. and a larger CID one at that.

Soundguy

[john_bud]

Originally Posted by john_bud

First off, you do know the difference between a 3cyl and a 4 cyl, right?

One has an additional cylinder.

That's about it.


jb

I stick by my comment! (the rest is just "bench racing" so he can get bragging rights with the buddies....)

jb

[Mickey_Fx]

Originally Posted by Egon

There is no answer as there are just too many design considerations to account for.

The only definite the more cylinders the more power pulses the better the chances of smoother operation depending on cylinder configuration.

Don't overlook the fact the 4 cyl has a single plane crank and the 3 cyl has a 3 plane crank. The 3 cyl will be more inheritly in bal. All else being equal, the 4 cyl will have more but less intense power pulses.

[RobJ]

Originally Posted by Mickey_Fx

Don't overlook the fact the 4 cyl has a single plane crank and the 3 cyl has a 3 plane crank. The 3 cyl will be more inheritly in bal. All else being equal, the 4 cyl will have more but less intense power pulses.

I'm not so sure about this, a diesel has a huge heavy flywheel to smooth out things plus the more cylinders firing the smoother the engine....less time between pulses.

Rob