# Odd numbered cylinder engines...



## 357 (Feb 24, 2006)

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?


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## yuandrew (Feb 25, 2006)

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


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## cy (Feb 25, 2006)

Citroen 3CV


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## Trashman (Feb 25, 2006)

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.


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## ABTOMAT (Feb 25, 2006)

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


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## IsaacHayes (Feb 25, 2006)

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..


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## gadget_lover (Feb 25, 2006)

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


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## bjn70 (Feb 25, 2006)

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.


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## gadget_lover (Feb 25, 2006)

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


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## AngelEyes (Feb 25, 2006)

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


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## Radio (Feb 25, 2006)

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


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## cbxer55 (Feb 25, 2006)

AngelEyes said:


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


 
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.


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## cbxer55 (Feb 25, 2006)

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.


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## BB (Feb 25, 2006)

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


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## cbxer55 (Feb 25, 2006)

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.


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## 357 (Feb 25, 2006)

AngelEyes said:


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



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.


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## IsaacHayes (Feb 25, 2006)

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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## scott.cr (Feb 25, 2006)

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



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.


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## sniper (Feb 25, 2006)

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!


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## 357 (Feb 25, 2006)

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).



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?


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## 357 (Feb 25, 2006)

scott.cr said:


> 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.



Is there a reason inline 4s have such intense vibration then? Is it just that they don't make 4s with quality parts and labor (because most 4s are in "value" cars)?

Even higher end 4s I've test drove have vibration, including the 4 cylinder Hilander and Camry--no where near as bad as the Civics, but no where as quiet and refined as my V6.


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## rayearth (Feb 25, 2006)

I don't know much about car engines, but from what I've gathered over the years, the only inherently smooth car engines are the inline 6 and V-12. Everything else will vibrate/rattle. The trick is using the appropriate clycing counterweights to counter the inherent instability. The reason why the I-6 isn't used often is that it tends to be a fair bit longer than the V6 commonly seen, making it harder to fit into a car's style.


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## alaskawolf (Feb 25, 2006)

i miss my RX7s Rotary , very smooth and high reving


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## gadget_lover (Feb 25, 2006)

357 said:


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



I'm pretty sure it's because the per cylinder displacement is larger and the exhaust flows less smoothly. A 2 liter V6 will have 1/3 liter per cylinder, but a 2 liter 4 will have 1/2 liter per. That's close to the size of a harley davidson cylinder. 

I could be terribly wrong.

Daniel


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## Agent_K (Feb 25, 2006)

alaskawolf said:


> i miss my RX7s Rotary , very smooth and high reving



I miss mine too. Although I don't miss the buzzer that went off at 8000 RPM :naughty:


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## simbad (Feb 25, 2006)

The top Volkswagen Touareg 4x4 version comes with a V10 TDI engine, it doesn't make ANY noise as a diesel engine at all.
Like CY said above the Citroën engines are quite particular, 60's and 70's models are based in 2 and 4 cyl. Boxer air cooled, I think the original 3CV model was 2 cyl. 480 cc. air cooled, then the GS model (looks like a small DS) came with a 1300cc. 4 cyl. Boxer air cooled/oil radiator. After 1985 Citroën changed the engineering back to "normal" engines like 4cyl. in line liquid cooled for both diesel/petrol versions.


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## cbxer55 (Feb 25, 2006)

scott.cr said:


> 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.
> 
> 
> This is somewhat true. The inline 6 is smoother that a 4 for one reason. On a inline 4 you have 2 pistons hitting top and 2 hitting bottom simultaneously. On the inline 6, you have 2 hitting top, 2 on the way down and 2 on the way up.
> ...


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## snakebite (Feb 25, 2006)

cbxer55 said:


> 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.
> 
> ...


my "water buffalo" had the same pipe setup.
my neighbors said it sounded like a giant popcorn popper.


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## PlayboyJoeShmoe (Feb 26, 2006)

Back in about '95 I was driving several different cars for a fuel test for Shell Oil Co.

Two stand out. I can never remember the model name but it was a small GM car (Buick I think) with a 4cyl engine that was *ROUGH AS A COB!* and a Toyota Camry 4cyl that was not bad at all. Has to do with balancing and assembly care I would think.

Man o MAN! The inline 6 Cummins is a _smooth operator_ .......


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## BB (Feb 26, 2006)

Here is an article that dicusses the issue of 4 cylinder engines and the need for a 2nd order harmonic balancer--it is not just a better built engine--it is adding a second (one or two) rotating shaft running at 2x of the fundimental engine RPM:

Wekipedia:



> The basic concept behind balance shafts has existed for nearly a century and is no longer patentable. Two balance shafts rotate in opposite directions at twice engine speed. Equally sized eccentric weights on these shafts are sized and phased so that the inertial reaction to their counter-rotation cancels out in the horizontal plane, but adds in the vertical plane, giving a net force equal to but 180 degrees out of phase with the undesired second-order vibration of the basic engine, thereby canceling it.



It has been many years--but as I am reading around--I believe that a 90 degree V8 naturally balanced both first and second order harmonics (not just first order as I typed earlier).

-Bill


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## markdi (Feb 27, 2006)

balance shafts suck (power)

I am glad my 2.3 dohc 16 valve w41 ho quad four does not have them.


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## cratz2 (Feb 27, 2006)

Whether based on fact or just blind belief, I'm a big believer in inline 6 engines... whether in BMWs or in diesels. 

I used to own a 1993 Geo Metro XFi which had an inline 3. It wasn't a rough engine, but it was so small and underpowered, it probably didn't have enough power to be rough! 

But I've had I4s, I6s, V6s and V8s... but not really enough of each of similar vintage and wear to really draw any conclusions. In the past 5-7 years, the NVH of vehicles (that is, noise, vibration and harshness) has had a lot of effort put into minimizing those factors. Front wheel drive, OHV GM vehicles still seem particularly un-smooth to me, but a few vehicles actually have 2 dampners on the crank now... My buddy has had two TrailBlazers with the inline 6 while he previously had two different Jimmys with 4.3L V6s and I had a Blazer with the 4.3L V6. Without a doubt, the inline six is smoother and more powerful.

I also wonder why so many 6 and 8 cylinder engines are Vs. I mean, there are flat 4s and flat 6s, inline 6s yet probably 95% or more are Vs. Having said that, it is super easy to do a tune up and spark plug and wire change on an inline 4 engine. I could literally do my 99 Civic Si with one hand once the hood was open. I haven't looked at any of the current inline 5s but if they are as easy to work on as the 4s, then I see some appeal right there. The V6 Contour and my V6 Sterling both were nightmares to change the last one or two spark plugs.


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## IsaacHayes (Feb 27, 2006)

Just want to add, that 60degree 6cyl is naturally balanced. The 90 degre 3800 series of motors from GM have balancing shafts though. you can disable them but it's rougher around low rpm.
90d v8 is natrually balanced, as well as a 60degree v12.


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## cobb (Mar 4, 2006)

Ive liked odd cylinder engines as they seem to give more torque and more power than a 4 in a smaller package than an i6. Also, I think you have more main bearing caps than an i6 if I also recall correctly.


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