The car shown in my profile pic lost 5mph of top speed after the
ad hoc repairs after a collision. I think it was mostly from the elephant-ear fenders, not the always-popped-up headlights. That left headlight was like sighting down a laser pointer driving at night, but the whole nose from the A-pillar forward was replaced eventually.
Since we have OP and aerohead together in the thread, what do you think of this? It's the Theoretical Template, truncated with an exponential bell for a difusser.
The thinking is that the curved bottom edge would form vortexes that implode the wake compared to a straight edge.
The thinking on the Dasher was to put a kick-up in the undertray and have a wing on the axle that would apply to unsprung weight directly, but it's too complicated by the exhaust and gas tank.