different 318 question

318 is just an overbored 273. The top end was designed with a 273 in mind. 318 is closer to 340 size than 273. Breathing at high rpms isn't its strong suit. The heads are the cork for power on 318 but saying that they are good for about 300 hp unmodified.

Theres a build with a dead stock long block 4bbl headers and xe262h cam and makes 282 hp @ 5000 rpm. Thats probably the biggest cam you want to go with stock cr.

Your cam choice would probably be a better street and make close to the same hp. Even 256 ish cam is a step up from stock.