Long tube headers on my 72 duster 318

A lot depends on the level of power you have or looking to gain based on the engines specs. Typical gains of just plain old headers on a 340 are around 25-30 HP, less on a stock 2bbl. 318 though the addition of a good manifold and 4bbl. Provide similar gains like the 340.

A small cam, headers into a 2-1/2 exhaust, manifold and carb on a stock low compression 318 can produce 270+ HP while running on 87 octane. It can have the ability of turning high 14's with ease. I did it with a 8.5-1, 318 a split duration cam and the above mentioned mods with 3.23 gears and a stock tire. Adding 4.10's & a 4spd brought me into the 13's in my Cuda.

The engines respond well to modifications and respond really well to a group of mods matched for RPM and purpose. Good mileage can be retained with small camshaft sizes and reasonable gear ratios.