Okay, keeping the tech relatively basic, the 318 suffers from a lack of static compression from the factory mainly due to the pistons sitting way below the deck surface at TDC. What this means is that dynamic compression (which factors in rod length and cam timing) can become unacceptably low with a long duration cam. You want a cam which closes the intake valve relatively soon after the piston reaches BDC. All else being equal, this means shorter duration on the intake lobes.
I'm sure others could chime in with specific cam recommendations but something like a Comp 270H Magnum grind might be a good choice or a little milder with a High Energy 268. Other brands are available!