even someone with an old Pro-Logic unit can answer that.
a five speaker setup (i only have five plugin areas to work with) will have the majority of both the engine sound and exhaust sound coming from the rears. GT4 had it set up so that the engine clatter and wind whistle came from front, the exhaust burble from the rear, on conventional cars. as I'm set up with the music, I haven't noticed what the left and rights get.