I put a MSD ignition on my 91 Blazer last month. A 6A, coil pack and superconductor wires. Gas milage stayed at 13 MPG but the extra performance was incredible. Thanks all who steered me away from Jacobs. I was going to complain about my milage untl I read stuff from a couple of pages back. I have the off-road and the heavy duty hauling package. 4.10 gears and stock 31X10.5. Two questions, 33's on a stock Blazer but with Bushwacker cutouts is my idea, but will it work. Seems that 14 bolt ff is liked alot, but what about a 14 bolt sf?