Why less cylinders?

[cRiPpLe_rOoStEr]

A bigger # of cylinders have been turned into a premium feature, more than anything. Spending more money for something that would work less efficiently sounds dumb, but many folks are glad to do it...

[kamesama980]

Marketing. No matter the displacement, no normal, unintelligent member of the human masses is going to pay for a 2l v8 in their compact car.

And all the technical arguments above: Thermal efficiency, Friction, etc.

[ksa8907]

Torque=force×distance. If you shorten the stroke and leave force unchanged, you get less torque.

[RobertISaar]

Originally Posted by ksa8907

Torque=force×distance. If you shorten the stroke and leave force unchanged, you get less torque.

you also have less displacement. make up the difference in displacement via a larger bore and torque will be quite similar to what it was before changes. possibly better, since the valves won't be as shrouded.

then there's the whole "a shorter stroke will allow longer rods" argument that comes up in certain circles.

[baldlobo]

i only know of one instance where a 6 cylinder vs. 4 cylinder is actually benifical.

any 4 cylinder over 2l creates a secondary harmonic, that can distroy engines; harmonic balancers are needed along with heavier crankshafts.

where as the 6 cylinder needs none of that.

gm engines
2.5l I4 110hp; 2.5l v6 145hp; 2.5l I6 154hp

195ci pontiac I4 vs buick 3.0l v6

[jeff88]

Originally Posted by baldlobo

any 4 cylinder over 2l creates a secondary harmonic, that can distroy engines; harmonic balancers are needed along with heavier crankshafts.

where as the 6 cylinder needs none of that.

gm engines
2.5l I4 110hp; 2.5l v6 145hp; 2.5l I6 154hp

195ci pontiac I4 vs buick 3.0l v6

Can you explain further the secondary harmonic issue?

Also, on the GM engines, how does the 2.5l V6 and I6 get better HP? That is what I was trying to get at with the original question.

[user removed]

In 4 cylinder engines of over 2.4 liters the force of the first and last pistons combustion can develop a rocking motion in the engine from front to rear. This is due to the portion of the energy that actually moves the engine block in the opposite direction of the pistons.

I think it was Mitsubishi who developed the countershafts, typically spinning at twice engine speed that counteract that force.

Basically the reason fewer pistons is more efficient, is the physics of the area of a circle.
Pie R squared. The greater the radius the exponentially greater the area.

regards
Mech

[cRiPpLe_rOoStEr]

Originally Posted by baldlobo

gm engines
2.5l I4 110hp; 2.5l v6 145hp; 2.5l I6 154hp

It's not so much accurate to say a 6cyl would be better just based on horsepower. Look at the 2.4L LE5 engine with its 169hp...

[wobombat]

I've heard of tractor engines with one huge cylinder that fires once every four or five seconds, and I bet it produces power rather efficiently, considering the low number of explosions per minute and the very small number of moving parts.

[cRiPpLe_rOoStEr]

Originally Posted by wobombat

I've heard of tractor engines with one huge cylinder that fires once every four or five seconds, and I bet it produces power rather efficiently, considering the low number of explosions per minute and the very small number of moving parts.

That also leads to another point: the selection of a more efficient gear ratio to deal with the torque pulses