managed to find some webbies about this, you may wanna check it
out
http://auto.howstuffworks.com/question366.htm
http://answers.yahoo.com/question/index?qid=20060831160741AAfkghH
taking 6 cylinders engines for examples...
To put it simply, straight-6s are capable of higher horsepower ie,
800-1000bhp GTRs and Supras. The pistons travel just up and
down.... 3 up 3 down at the same time. imagine a hammer hitting a
nail... the greatest effect is when hitting directly above
it.
V6s has the advantage of higer torque and more cubical design; more
compact than the long straight-6. Power-wise, why it doesnt develop
as much horsepower as the S6 is cos the end stroke ends up at 2
places; the downstroke of one side of 3 cylinders goes to, say
bottom left while the other ends at bottom right. the combustion
energy is more spreaded out, unlike the S6 which is more towards a
focal point, which is basically down straight. But it gives out
more torque; each downstroke at is 2 location, from left and
right... hope you get the idea 
Both types have their pros and cons, so you cant really say which
one is definately better.
Why BMW engines are more powerful is cos they have a complex
electronic engine managment system, that continously makes
adjustment to the cams and valves to give peak performance. The
Mini One and Mini Cooper both uses the same identical engines, yet
the One only produces 90bhp while the Cooper puts out 120bhp. The
difference is the engine control unit, that controls how the engine
runs. The One has a springy performance with better fuel economy
while the Cooper has a more punchy feel.
