Originally Posted by Sick88Tbird
Be careful how much work you put into that 403...bottom ends aren't the toughest in the world, what with the windowed blocks and all. They can handle the typical carb, intake, exhaust mods well, as long as you don't rev the living daylights out of it.
True. 4500 rpm is about all theyll breathe to, but don't worry, you can make it very quick even with that.
I had a '78 403 T/A and two fellow club members had '79s with that engine. All of us used simple 2 1/2" dual exhaust with 3 chamber flowmasters, headers with a crossover pipe a little behind the collectors, recurved the distributor for a few more degrees of advance, and rejetted and tuned the quadrajet for a bit more response. No other changes (never even had the heads off). With the 2.43 rear end ratio and a B&M shift improver kit in the trans, the cars went from being 16.5 second quarter mile cars to high 13s. When my friend swapped to 3.55 rear end gears, the 4500 rpm redline hurt and the car actually slowed down in the quarter as it got to top speed about 3/4 of the way down the track... 3.0 gears might have worked, or even 2.73's...