I've seen A LOT of posts about making HP with a 318-So why is it so ???

PRH said
Possibly a little.
The 30hp from the 650-2bbl was actually more of an improvement than we expected.
That’s the only motor we tried it on.

Several years later, when the 360’s/350’s/351’s were what was being run in that class, and the Chevies were running the Vortec heads........
a really good 355 Chevy Vortec combo would pick up 40-50hp from the 4412 to a good 4bbl.
One that didn’t use all the good stuff...... which could be down close to 20hp with the 2bbl....... would only gain about 30-35hp with the 4bbl swap.

That's strange I find that low, EVERY single time I have gone from a 4412 to a 650,750 etc... It was 60-70 hp change. The first time ever it was a 383 SBC--430hp with a legal 4412--stuck a 650 dbl on and 503hp. I also tested a W2 headed 360 I built---447 hp with a 4412---650dbl= 527hp. I've done numerous other SBC's and when troubleshooting have switched from a 4412 to a 4150 and have never seen less than a 60hp gain. Usually 70hp. Thanks for sharing Dwayne. J.Rob