Is this engine builder nuts?

The key to making power is all in the heads everything else is there to support it. 273/318 heads where designed for a 273 and for that engine there good flowing but not for a 318 which is 45 cid bigger. They can be made to work or ok stock if your looking for 300 hp or less but there not really worth the time and money when looking for more. With low flowing heads you need a lot of cam and CR to squeeze every last hp out of them. Or the better way like the new Hemi's or LS is to put really good flowing heads and smaller cam so you get power and drivability.

Now engine size look at it as a powerband selector, most engines have a 5000 rpm powerband give or take and cubic inch don't make hp. With similar parts 318,340,360 and 408 etc will make similar power but at different rpm. So 350 hp 318 will make peak around 6000rpm and a 408 would probably be under 5000rpm.

And torque is a 2 part equation everyone looks at crank numbers but it's the torque to the ground that matters. So most decent engines will make 1.1:1 - 1.3:1 torque to cid. Thats why bigger engines rule the street is cause most people only want to run 3.23 -3.91 gears which is way under geared for most engines to get max performance out of them. Since torque is proportional to engine size so is gearing. Take a 3.55:1 525 lbs-ft 408 and take 2.74:1 first gear times 3.55 and 525 equals 5100 lbs-ft to be divided by the tires. Since a 318 is about 72 % smaller it needs 28% more gear (100% - 72%) so a 318 needs 4.56 plus to even come close to the acceleration of the 408 and a Max performance 408 probably needs around 4.10 and a 318 would be 5.13 plus range. So you can put the torque in the engine (size) or the rear gear so when it comes to building smaller engines if your ok with gearing it then build it if not move up the cid ladder.

I concur with the 360 magnum, the old 300 hp create motor was a dead stock 5.9 and with headers said to make 320 hp with cam up to 400 hp and after market heads 450 hp and if you get a low mileage or decent one you can get away without rebuilding for now. $$$$