I was going to ask fb this question, but decided FSAE.com was more appropriate:
Most FSAE teams running 4 cylinders use headers/extractors, either a 4-1 or 4-2-1. Is there a really obvious reason that I'm missing why I've almost never seen a team run a manifold (like on a production car)?
There seem to be a lot of benefits in cost/packaging/mass/simplicity/etc. The main drawback is power, but less power = less fuel used. And in FSAE-A, singles (that weigh more than a good Euro 4 cylinder team) have enough power to go very fast.
We plan to do the analysis to see what power loss can be expected, but I seem to remember when I asked for numbers in 2011, it was in the order of 5-10kW loss.