We usually call that a strake. It can be called a forebody strake, or a leading-edge extension, or a vortex generator, or other names as well.
Its purpose in this case is to delay the early flow separation (stall) that occurs on (some) RV-8s because the flow over and around the landing gear leg and its junction fairing disturbs the wing flow at high angles of attack.
Some people report that the bad flow characteristic is influenced (either for good or bad) by the shape/size of the junction fairing. I found that it was about the same with or without the fairing.
Some pilots report feeling the buffet in the stick as the separated flow hits the horizontal tail. I find that it causes some funny whooshing noises and mild buffeting on the fuselage side.
In any case, helping to keep the flow attached through there can lower stall speed by several knots. Some folks that have installed them report little or no impact on cruise performance.
