if there were more exhaust outlets on an F1 car, would aerodynamics (downforce) be improved? what would be the optimum place to position the exhausts and the optimum number of exhausts?
McLaren, amongst others, used to blow the exhaust gases into the diffuser, energizing the flow and creating more vacuum under the car. The problem was that these aerodynamics were throttle-sensitive. If you want to see what it looks like, read the latest Racecar Engineering.
Bring back wider rear wings, V10s, and tobacco advertisements
The optimum number of exhausts (you mean exit pipes I presume) is set by the requirements of the engine for most efficient extraction & cylinder filling.
The exhaust outlet position is very important for aero peformance. To ask the question "is there a optimum position" is the wrong question. Every part of a car affects another part, so you wouldn't design the aero around the exhaust - it is part of the overall picture starting at the front of the car. So, you wouldn't decide the optimum exhaust position until you had a good picture of what the rest of the car is doing. I would imagine that the exhaust outlet position is not just decided by aero; also length required for the engine and position of the cylinder heads contains it to a certain area of the car - then managing heat under the engine cover (suspension arms, dampers etc.) would also be considered.
In the interests of engine efficiency, having a 5 into 1 exhaust is better than five individual pipes. (for this application). An exhaust system, despite the fact it has no moving parts, is an incredibly complex device. It would take a week to explain how a formula one exhaust system works. For instance, if you look closely, the diameter of the pipes leaving the engine block gradually grow larger as the approach the 5 into 1 collector.
As far as their effect on aero, it can be huge. Do the math. A 3 liter engine turning 19,000 RPM pumps 28,500 liters of hot exhaust out the back every minute. That's a lot of hot air, and since RPM's change, can affect the balance of the car if that exhaust has an influence on the rear wings or aero bodywork. So where and how the exhust is discharged is of major importance.
To answer the original post, what you see currently is considered the optimal solution.
