Odd numbered cylinder engines...

What are the advantages / disadvantages of odd numbered cylinder engines?

I see Volvo and VW offer 5-cilinder engines. GM at one time offered a 3-cylinder engine on the Geo.

Wouldn't an odd clylinder engine be more complicated?

Mercades 300D; 5 cylinder Diesel engine

GM is currently offering a odd cylinder engine; the Vortec 3500 3.5 liter inline 5 on the Hummer H3 and the Chevy Colorado/Canyon Pickup

Citroen 3CV

The Ford Fiesta used to have a 3-cylinder engine. GM advertises their current inline 5-cylinder as having the power of a 6-cylinder while getting the good mileage of a 4-cylinder.

My lasting impression from driving around in a friend's 5-jug Volvo is that it's a really rough engine.

Acura Vigor, and TL had a 5cyl.

I always wanted to make a straight inline 7 cyl. With a long bonnet and make it a 2 seater. I think that would be swell!!

Only thing i can see as being more complicated as it may not be naturally balanced and need balancing rods..

The advantage is fewer cyclinders = less resistance to overcome. In theory a 5 cyl 2 liter engine will produce more power than a 6 cylinder 2 liter engine.

The offsetting problem is vibration. In a 4 cycle engine with an even number of cylinders it's fairly easy to set it up so that pistons move in pairs, canceling out each other's vibrations. Even the firing order is carefully planned so that the cylinders firing in a stready sequence. Make it an odd number and you have to resort to harmonic balancers to get a fairly smooth running engine.

Gee. 30 years of reading Popular Mechanics paid off!

Daniel

In a "V" engine I would think you would want an even number of cylinders. Otherwise you can pick the number that fits and best achieves the displacement you want.

We're used to I4 and I6 engines, otherwise an I5 would probably seem perfectly OK.

I seem to recall that the inline six cylinder is mechanically inherently balanced. Per a web post....

"The pistons are balanced by pistons, connecting rods by connecting rods, the crank is balanced. Even the camshafts are balanced on the Inline6"

What they are saying is that while one is going up, one is going down. There is a power pulse every 60 degrees of the crank rotation (IIRC) . Add or subtract cylinders and you will have something moving that is not counterbalanced.

Of course, some great counterbalances have been used in cars for many, many years, so it's kind of accademic in modern times. I had a 2 cylinder 600 CC bike with harmonic balancers in the early 70s. At the right speeds it was a smooth as a 4 cylinder. Hated it.

Daneil

I

A 3 cylinder engine just sounds like a lawnmower. Btw, there are 1 cylinder mopeds or motorcylces too.

My friend just bought a GM H3 Hummer 2006, it has an 225hp in line 5 cylinder, seems very nice

AngelEyes said:

A 3 cylinder engine just sounds like a lawnmower. Btw, there are 1 cylinder mopeds or motorcylces too.

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I guarantee you the 3 cylinder engine in my 1972 Suzuki GT750 does not sound like a lawn mower. But what do you expect from a 3 clylinder two-stroke woth expansion chambers and K and N filters. Sounds like a well tuned outboard, and smokes to break the bank!

The in-line 6 in my 1981 Honda CBX is exceptionally smooth.

There is a power pulse every 60 degrees of the crank rotation (IIRC) .

There is a power pulse every 120 degrees of crankshaft rotation. Remember that on an inline 6 the cylinders are paired up. ! and 6, 2 and 5, 3 and 4. The crankshaft spacing is 120 degrees, 360 divided by 3 = 120. Firing order on my 1981 Honda CBX is 1,5,3,6,2,4. 1,5, and 3 first revolution,6,2, and 4 second revolution. This results in 3 power pulses every revolution, and three exhausts every revolution.

The old radial (round) piston aircraft engines (such as Pratt and Whitney) where odd number of cylinders per row (9, if I remember correctly). The older aircraft radial engines were available in 3, 7, and 9 single row cylinder configurations. Why, I do not know but suspect that natural balancing properties are part of the reason.

The advantage of a 90 degree V8 was that the primary frequency rotating/moving mechanical forces where in balance. The secondary and higher harmonics (2x frequency and higher) where not, but they are lower in amplitude than the primary--therefore less of a problem (from a college calculus exercise several decades ago).

-Bill

Ther reason that radial engines are odd numbered is simple. The cylinders do not fire one after another. First revolution the odd numbered cylinders fire. Second revolution the even fire. therefore 1,3,5,7,9,2,4,6,8. This sequence is the same for a inline triple four stroke like Triumphs and the older Yamaha XS-750/850. First revolution 1 fires,2 exhausts, 3 fires. second rev. 1 exhausts, 2 fires, 3 exhausts. Third rev, back to beginning. This sequencing does not work with even numbers.

AngelEyes said:

A 3 cylinder engine just sounds like a lawnmower. Btw, there are 1 cylinder mopeds or motorcylces too.

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Most 4 cylinder engines do to me as well (such as the engine in my old Civic--which I sold about 1 year ago).

I won't buy anything smaller than a 6-cylinder these days for this reason, plus the 6's seem to have less vibration at idle than the 4s.

357: I tottaly agree. 6's have less vibration all around. A lot quiter (even with a loud exhaust they are quiter unless you floor it, then it's got some rumble).

I seem to recall that the inline six cylinder is mechanically inherently balanced.

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Actually, any engine with an even number of cylinders in a straight configuration is balanced. That's because you have an equal number of crank throws 180 degrees out from one another.

When balancing the crankshaft of a straight engine w/ even numbers of cylinders, you simply throw the crank on the balancing machine.

With vee engines and engines with external balancers you have to either put all that stuff on to the crank before balancing, or weigh each piston/ring/rod/bolt combo and make a simulator weight (a "bobweight") and then put the whole thing onto the crank balancing machine.

I once saw a Harley crank on the balancer... probably a similar config to the radial engines being discussed. I could barely lift the bobweight with one hand.

My Trailblazer has a 6 cyl. in line engine, and I like it! No difference noticeable from the V-6 I once figured was the minimum necessary.

All radial engines have an odd number of cylinders, and they did quite well in the Focke-Wulf 190, the Grumman Wildcat, Hellcat, Bearcat and Tigercat, as well as the Skyraider and Corsair, not to mention the Japanese Zero and the P-47. There are a few aircraft that still use radials, and they are a delight to hear when they are flying. Ohhhh, yeah!

IsaacHayes said:

357: I tottaly agree. 6's have less vibration all around. A lot quiter (even with a loud exhaust they are quiter unless you floor it, then it's got some rumble).

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Is there a mechanical reason why the 6s and larger engines are more quieter than the 4s?

Or is it just that the pitch of the 6 cllinder engine is less offensive on the ears than the higher pitched 4?