Big horsepower 318 builds

273 said
I don't get this one, don't know why you would say that?

To me there two main ways to go about building an engine for a certain powerband and gearing or for a certain hp level and gear and stall to work with the final powerband results. To a point most are a combo of the two.

The 1st one say you pick 3.23 and idle to 5000 rpm with peak hp being about 5000 rpm, obviously since rpm is fixed torque is the only main way you can build NA power so the bigger the engine the more hp you'll have most street type engine fall into category.

2nd is to pick say 500 hp and pick a displacement and build.

So a 318 vs 360 vs 408 you would have to displace a certain amount of air, there's a rule of thumb saying about 1.4 cfm for every hp, not carbureted but actual displacement (1.4cfmx500hp=700cfm) so if you run a 390 cfm carb or a 1000 cfm carb the engine is gonna pull 700 ish cfm's through either.

At 100% VE using cid x rpm / 3456 = cfm

a 318 would need to spin 7608 rpm to displace 700 cfms
a 360 would need to spin 6720 rpm to displace 700 cfms
a 408 would need to spin 5929 rpm to displace 700 cfms

Obviously depend on how well you design your combo they can overlap eg. a poorly built 360 peaking at 7200 rpm and a well put together 318 peak at 7100 rpm but I don't think you could build the 408 terrible enough for the 318 and it to have similar powerband.

So I guess yes there's exception and I guess there's enough variables to make it, "it's just a theory", but it's generally true smaller needs to spin higher.

To get out of the minds "318 vs ***", lets look at a single cubic inch. 360 per say. Some build them to shift at 7200 rpms all day and do it going 11's in the 1/4. Some build them and shift at mid 6k and run mid 9's. Why would that be?? Because it's about how well the heads are flowing, and a cam to match, and a intake/carb to sit on top of it that compliments the design of the build. I bet my 318 makes more power at 5000 rpms than a stock '73 340, and I have less of just about everything. Why would my smaller engine make as much or more power at the same rpm??? Is it my smaller valves? Or less compression? I don't say this sarcastically, I say it because there is a theory that one HAS to spin the daylights out of the smaller engine to make equal power. Simply not the truth.