Has anybody done any upgrades to these 502 MPI motors? I have had my ecm reprogramed and changed to a K&N filter which gained me a little more power. What about changing and/or modifying the heads, cam or intake? If so what heads or cam do you guys think will be the best to go with? What kind of cost are these upgrades going to be? No, I don't want to Whipple it or procharge it. I'm just looking to make another 50 or so hp. What is the difference between the 500hp and the 502 MPI besides about 55 hp? Thanks for any constructive input.