I don't think anyone has done a dyno test on a stock engine and then installed the magnum parts for a comparison so how much horsepower does the conversion gain? A stock 318- 2 barrel usually puts out 230 horse and with the magnum heads and a 4 barrell , headers, and a good cam, you can get close to 400 hp. Mopar Muscle did a 400 hp 318 with magnum heads. Here's the link: