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What is the advantage of a V (or horizontally-opposed) engine over a straight engine?

So a straight 8-cylinder engine has its pistons arranged equally about 360 degrees - ie one every 45 degrees? And a V engine has them *effectively* at the same spacing, if you allow for the angle of the V. Fair enough - makes sense. Given this, I've always wondered why 4-cylinder engines don't have the cylinders every 90 degrees, instead of two at 0 degrees and two at 180 degrees. Would it cause even more vibration if successive cylinders counting from one end were at 0, 90, 270 and 180 degrees rather than 0, 180, 180 and

0? Either way you avoid a travelling wave of vibration (0, 90, 180, 270 or 0, 0, 180, 180 would be a Bad Thing!).

One other thing. Someone mentioned radial engines, as used in aeroplanes. Am I right I thinking that some radial engines had the propeller attached to the engine block and rotated all the cylinders about a stationary crankshaft that was attached to the fuselage? Have I really understood that correctly? If so, you'd think that getting the fuel fed through what is effectively a commutator (in electric motor terms) from stationary fuel supply in the fuselage would have been a little bit tricky, even if you had rotating carburettors and separate exhaust pipes for each cylinder. Why did they do it this way rather than having the cylinders fastened to the fuselage and rotaing the crankshaft and propeller?

Reply to
Martin Underwood
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Of course there are qualifications...

Here is a general clip from Wikipedia, however "The straight-6, flat-6, and V12 designs have none of these forces or moments of vibration, and hence are the naturally smoothest engine designs. (See the Bosch Automotive Handbook, Sixth Edition, pages 459-463 for details.) Engines with particular balance advantages include:

a.. Straight-6 b.. Flat-6 c.. Flat-12 d.. V12 Engines with characteristic problems include:

a.. Flat-4 boxer and straight-4 have no better kinetic energy balance than a single, and require a relatively large flywheel. b.. Crossplane V8, which requires a very heavily weighted crankshaft, and has unbalanced firing between the cylinder banks (producing the distinctive and much-loved V8 "burble"). c.. Flatplane (180° offset crankshaft) V8. In modern multi-cylinder engines, many inherent balance problems are addressed by use of balance shafts."

Balance is an interesting subject.. A lot of things can influence the way you choose to balance a particular configuration.

Reply to
<HLS

In terms of vibrations, yes. A "boxer" 4-cylinder has some residual imbalance, but not NEARLY as much as an inline 4.

Reply to
Steve

Nnnnnnno. You're forgetting that most car engines are 4-cycle engines. An 8 cylinder engine fires only *FOUR* cylinders for each turn of the crank, or a combustion cycle every 90 degrees of crank rotation. The remaining four cylinders fire on the next turn of the crank. For a

4-cycle engine with an even number of cylinders to fire at uniform crank rotation, the cylinders have to move in pairs. One of the pair is on its combustion stroke while the other is on its intake stroke.

And a V engine has them *effectively* at

See above. A 4-cycle 4-banger needs to fire a cylinder every 180 degrees.

Reply to
Steve

The other advantage to engines with numbers of cylinders greater than 4 is that a 4-cylinder, 4-stroke engine has no overlap between power pulses so power delivery esp. at low RPM will always be a little rough. A 6- or 8-cylinder engine does not have this problem, so power delivery is creamy smooth.

most of the cars I've owned have had 4-cylinder engines simply because they're more economical (generally,) but I do miss my '67 Dart and '86 BMW... a well tuned straight six is a wonderful thing.

nate

Reply to
Nate Nagel

all i really know about the subject is if u took the same number of pistons and stroke and bore the inline motor will have a lower redline increasing the torque at lower rpms while the v will more often that not have a higer redline and move the power further up in the rpms.

Reply to
midgetracing28

That would really depend on the cam, the weight of the rotating assembly, manifolding, and lots of other things. There's absolutely no

*fundamental* reason that an inline of the same cylinder configuration would have a lower torque band.
Reply to
Steve

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