3 cylinder vs 4 cylinder debate

[BrokeFarmerJohn]

So I have been doing research on 3 cylinder vs 4 cylinder Diesel engines.

Has anyone actually tested if a 3 cylinder is more fuel efficient? Or tested which one is smoother, quieter etc?

For example I have a Mahindra 5555 with a 2.7L 3 cylinder engine (55hp) I believe it’s same engine in 5570 (70hp). A friend has a LS 6168 with a 2.5L 4 cylinder engine (68hp).

It got me thinking which one was best. Not a tractor to tractor comparison but 3 cylinder to 4 cylinder comparison.

Note* (fun fact) my 3 cylinder rated 540 PTO RPM is 2059 engine RPM while the LS is 2500 engine RPM.

I have browsed and read a lot on this subject from multiple forums but most info seems to be opinion not factual testing.

 

[RickB]

Whether a machine (not just a tractor) has 3 or 4 cylinder engine is not a criteria I would consider for basing a purchase decision. Durability, reputation and performance of specific engines would be. Few if any measurable engine attributes are predetermined by counting the number of cylinders.

 

[workinonit]

I've never had a 3 cyd. Both of mine have been 4. And you need to throw turbo vs naturally aspirated in the discussion. Both of mine were turbos. As far as PTO. My tractor has switchable 540 to 540E (Economy) PTO. On my tractor standard PTO is 2400 engine RPM and economy is 1715 engine RPM. My old 5310 was exactly the same. I honestly would never own another tractor without economy PTO.

 

[BrokeFarmerJohn]

I've never had a 3 cyd. Both of mine have been 4. And you need to throw turbo vs naturally aspirated in the discussion. Both of mine were turbos. As far as PTO. My tractor has switchable 540 to 540E (Economy) PTO. On my tractor standard PTO is 2400 engine RPM and economy is 1715 engine RPM. My old 5310 was exactly the same. I honestly would never own another tractor without economy PTO.

My 05 JD 4320 was turbo 4 cylinder. The Mahindra and LS are both turbo charged.

I haven’t had ECO 540. It’s not as big of a deal for me because I don’t do much PTO work. Mostly loader work.

 

[workinonit]

I primarily was interested in it on my 5310 to run my PTO generator for extended hours. After I got it and used it, it is probably the single best feature on a tractor for me. Aside from the cab, which is the reason I traded up to the 5090.

 

[dodge man]

Both of my tractors were 3 cylinders, a Kubota 900cc’s, and a JD 1250cc’s (more or less) made by Yanmar. The Yanmar is smoother but idles at 1500 rpms, I think because it is smoother at such a high idle. The Kubota was rougher, at idle very rough, at about 1100 rpms and I would sometimes throttle up a little to smooth it out.

The Kubota was noticeably more fuel efficient and was rated at 23 hp. The Yanmar is rated at 25 hp and I expected it to feel stronger thinking it was derated to make it no more than 25 hp but it feels like 2 more hp than the Kubota. Both seem to be very solid engines.

 

[Egon]

If you want smooth step up to an in-line six.

 

[LouNY]

If you want smooth step up to an in-line six.

Yes, the little Waukashaw 6 cylinder in my Oliver 1550 was a very smooth and sweet sounding engine.
A little 232 cu. in. diesel making 50HP at 2200 rpm, they sounded and ran smooth, but when the loads got high and started pulling that engine down she wouldn't stay and lug but required a down shift and revs to keep going.

What I have noticed is that for comparable displacement engines with similar hp ratings the torque curve of the lesser number of cylinders seems to be flatter and start sooner;
ie.. a 3 cylinder seems to make its torque sooner then a 4 cylinder and have a bit better lugging power, the same when comparing a 4 cylinder to a 6 cylinder the torque curve seems to usually start lower and be flatter the fewer the cylinders, the more cylinders the smoother they seem to run.

 

[Tx Jim]

Some 4 cyl engines have balancer shafts that 3 cyl don't require.

 

[radios1]

the more cylinders an engine has, the less horsepower each one has to make, so more cylinders should mean longer longevity..

 

[ruffdog]

the more cylinders an engine has, the less horsepower each one has to make, so more cylinders should mean longer longevity..

But then you throw in engine design and configuration into the equation. Like diesel truck engines, some 6's were much more durable than some 8's were. Also, those old Deere's were pretty durable with less cylinders.

 

[Industrial Toys]

I have both 3 and 4 cyl Kubota enginess and I like the sound and vibration of the 4 better. Also, seems to start anytime with no glow plugs, although other matters might be at play there.

 

[jaydee325]

Testing is expensive so you are not going to find a lot out there. Manufacturers to test (a lot) but don't generally make their test data public.

Best source I know of is Nebraska Tractor Test Laboratory.

Probably won't answer the proverbial question, "what's best, 3, 4, 5, or 6 etc, etc cylinder diesels" but I think if you have the time to wade through all of this data, some generalities may become apparent.

 

[Mat4644]

Generally speaking once into larger HP engines 4 cylinders vs 3 will always be smoother. For a given total displacement a larger cylinder firing is a bigger bang that is more difficult to dampen. Typically better emissons and fuel economy also on 4s. Due to the large varieties of engines out there exceptions exist.

 

[Egon]

The inline six is naturally balanced!

 

[Egon]

Some 4 cyl engines have balancer shafts that 3 cyl don't require.

That痴 because an in-line four is not balanced!

Check out the balance of different cylinder and alignment arraignments.

 

[Cougsfan]

I think that this is a trick question. The number of cylinders doesn't have nearly as much to do with efficiency and smoothness of operation as do numerous other design factors. A certain three cylinder can be better that a certain 4 cylinder in these regards, while a different 4 cylinder can be better than that three cylinder. I agree all the answers you get her will be highly opinionated and non-factual.

 

[Sawyer Rob]

I agree all the answers you get her will be highly opinionated and non-factual.

That's for dang sure...

SR

 

[Industrial Toys]

I don't know. If they are based on peoples objective "experience", and not the old, whatever I own is best mentality, I think that's valuable.

I have a four cyl ISUZU on a generator and it's the smoothest engine I own, 3 or 4 cyl. That would be my choice, if the size fit, for everything.

 

[shooterdon]

I never asked or put the number of cylinders into my buying spreadsheet when I got my new tractor. Too dumb to know I guess.

I just started them and rode them for a while.

BTW, all else being equal it is the RPM's that determine engine life. It is a squared relationship. An engine running at 1500 RPM will last four times longer than one running at 3000 RPM.

There is a reason the industrial gen sets run at 1800 RPM.