Just bolt on a supercharger, and get 48% more hp!

Once upon a time, you could get the 43% increased HP from a supercharger option for your Shelby 289... http://choosingscars.blogspot.com/2006/11/once-you-could-get-this-supercharger.html#links for $435

Aint it cool when history repeats itself? It's a lot more expensive now though

Now, for $5,599, the ROUSHcharger increases the HP of your Mustang GT from 300 to 445. That's a 48-percent increase http://www.autoblog.com/2007/10/03/roush-adds-30-extra-hp-to-roushcharger/