Will an aftermarket 4-2-1 header give any better gas mileage than a
stock manifold for a '91 Civic Si? I wouldn't go out and blow a wad on a
new fancy one, but from looking at used prices on ebay, it seems they
can be had for pretty cheap. Also, I've thought about seeing what
salvage yards do with all the parts from 'riced out' Hondas.

Mark