Edelbrock 1801 500 cfm for 318

I say if you want the thunder series, go 650. It will work great for your 318, and will work great if you ever go 340/360.

On my 318 with factory manifolds/mild cam/2.76 gears and stock converter I gained 2 tenths by going from a 600 eddy to a 670 Holley. I gained another 2 tenths going from the 670 to the 770 holley. Ironically, the 770 also cut the best 60 ft times.