Quote Originally Posted by Mark in Oshawa
Not necessarily. A narrow engine would give aero advantages if the rules allow side tunnels and the like. That said, if the IRL dictates a flat bottom between the wheels, then the config of the engine will come down to the Center of Gravity. If you can make a V6 work for a lower center of gravity say than an upright inline 4...or if you can shoe horn a straight six in there and make it work, then all power to you.

The fact is, how the chassis minimum dimensions are laid out will be the final arbiter really of what engine config would likely work best.
You are only taking into account under-body aero.

A V-6 will allow for a lower engine cover while a inline-4 will allow for a narrower. Both effect rear-wing efficiency.

Of course there is not only center of gravity issues but suspension layout differences also.