Need more compression in my 318, does this add up?
Lol, you're not alone.
Reasoning? I'm still trying to follow youz guys on this cam stuff.
Sorry Bruce. I missed this.
Because at 9.5 or 9.6.......whichever, he will likely have too much cylinder pressure with a mild cam like the 268. The larger cam will have a later intake valve closing event and will start building cylinder pressure later in the compression stroke and create lower cylinder pressure allowing the engine to run easier on pump gas.
It "might" run on pump gas anyway with the 268, but it will be close.......especially in Summer idling in hot traffic during heat soak. He would have trouble IMO with detonation in that situation.
I don't like giving people advice that skirts the fence. Why take chances? Yeah, he can probably run 10.5 compression with perfect quench and yadda yadda yadda, but that's very costly to get that precise.
Doing it how I recommended is a lot cheaper and there's less room for error running on pump gas.
I like it when I build something I can actually drive and have fun with, instead of worrying about where I can find race gas.