Not sure what to do

To me there's two main ways to look at a performance build.

1st, build to a certain hp, and for the most part a 318 is basically just as capable as other engines for the general hp most build to, but generally you need more rpm and all that comes with it, stall, gears, idle etc.. Which may or may not be a problem.

2nd, is to build a certain rpm band, in the street generally 2000-5000/6000 rpm, with peak power in 5000-6000 rpm which can make huge difference to the engines behavior and power. But whatever rpm range your gonna build to. It's gonna have a typical hp to cid ratio varied by efficiency, obviously larger displacement are generally gonna make more power at those rpms especially if talking similar efficiency, but will need a lot more cylinder head etc.. to do it.

Basically if you know roughly the Hp you want and at what Rpm you want to peak at and how efficient (lbs-ft:cid) you can build it, basically gives you the cid you want.

Cid = (hp x 5252 / rpm) / (.9 x lbs-ft per cid )

1.2 lbs-ft:cid can be used as a general build (cr cam 4bbl headers)
1.25 lbs-ft:cid if aftermarket heads, roller/bigger faster cams etc..


Eg..
400 hp @ 6000 rpm, 1.2 lbs-ft = 324 cid
400 hp @ 5500 rpm, 1.2 lbs-ft = 354 cid
400 hp @ 5000 rpm, 1.2 lbs-ft = 389 cid