Well, the 273 two-barrel was rated at 180 horsepower with 45 cubic inches less. A hope the 318 was putting out more than a 273 or something is really wrong.
By those ratings the 273 would be down more horsepower as well. The difference is probably pretty close despite the numbers being lower on both sides.
Have to be careful using factory HP ratings though, comparing a motor with the same or more power at an extra 1000 RPM is not an equal comparison. That's part of why the LAs are as good of motors as they are- they were always built stock around usable and streetable power. The further from cruise speed the peak gets, the more the package is hurt by not having enough gear. Fine to run tall gears in a motor that peaks at 4200, but doing so in a motor that peaks at 6500 is mean most of its power will never be used. That's why the Magnum trucks weren't slower than the LS trucks or Hemi trucks they were sold beside- their gearing let them take full advantage of their peak where the higher HP trucks couldn't.
