is it a 390 or 391?? truck engine a 391 has a forged crankshaft and other hd stuff.the truck engines usually run out of steam around 4000 rpm. get a 428 and put your money in it,you will be a lot happier. a built 428 will hold its own with just aboutanything out there. and as far a eldebrock intake and heads go they could only get 400 hp out of it . that is real sad. info like that is for bench racers i go by what you can feel in the real world(seat of the pants).