I-6 versus V-6
 

the number of cylinders is not the primary reason for engine smoothness. an important factor is the way the engine is constructed, if it's an inline-, V- or boxer-engine:

inline-6:

-the inherent smoothness of an inline 6-cylinder design derives as follows: it has both primary and secondary balance. primary balance is when the crankshaft counterweights offset the weight of the piston and rod.

-secondary balance is when the movement of one piston balances the movement of another. V6's have a secondary imbalance that causes engine vibration. adding a counter balance shaft can reduce this imbalance, but that adds weight and complexity.

-there are some difficulties in designing an inline 6-cylinder: the length of the engine allows more harmful torsional twist in the crankshaft, and makes cooling all the cylinders evenly more difficult. stiffening the crankshaft helps reduce torsional twisting, and a front crankshaft damper helps control twisting forces.

(from: jim kerr, "canadian driver")

v6:

-the V6 is a special kind of V-engine. it is normally the case that two pistons, one for the left and one for the right cylinder bank, share a crank pin. in a V6 the crank pins have to be split and shifted in order to avoid vibration between banks.

-there are two kinds of V6 engines with different V-angles in use: 60° and 90°. the 90°-V6 has a 30° crank pin shift; the 60°-V6 60° shift.

-a V6 generates end-to-end vibration, so a balancer shaft is needed.

-thus V6-engines are inferior to inline six engines concerning smoothness, despite having the same number of cylinders.

-so why use V engines? although twice as much camshafts are needed, the higher friction, the lack of smoothness and the higher production cost, the V6 uses much less space, which helps saving costs in other places and allows front wheel drive (which saves further costs).

(excerpts from: http://www.e31.net/engines_e.html)

-an *excellent* reference site on the I6 v V6 debate, "engine smoothness," is here:

http://www.autozine.org/technical_sc...ne/smooth3.htm

:D

thanks for the info!

I think V12s are the only other engine to have primary and secondary balance.

The ultimate space-saver 6-cyl engine is VWs VR6. Not quite a V or an inline. Staggered cylinders.

Not quite so scientific but you forgot to mention that I6s sound better than V6s.:smilie_th

yes, the V12 is actually "better" than the I-6, as it is basically 2 I-6s, cabable of firing more frequently, thus, making the power delivery extremely smooth.