Why are 318's low HP and torque?

If your on a limited budget I'd leave the long block alone
4 barrel, cam and duals with or without headers plus shift kit and gears is the way to go. I read about a build up with a stock 318 they used Comp cam XE262H, M1 dual plane, 650 Holley and headers made 282HP @ 5000 even without headers still would make 250HP.
P.S. streetmaster intake isn't all that great of an intake but will do for now, than down the road you could go with better heads and intake.