Re: C5AE 289 Heads
I hate to tell you this but your comparing apples to oranges. Trying to compare a set of AFR heads to a stock casting is like comparing a mustang to a ferrari. The limiting factor is the casting. From the factory, Ford is only concerned that the engine runs, performs as advertised, and there are no problems. In the aftermarket, manufacturers are taking into consideration that their product is going to modified, and used the way they intend it to be used. To answer your question about performance, it really depends on the entire engine combination. On a well prepared super stock setup, where rules dictate that you have to run a factory casting, I don't see why a stock casting couldn't make 500hp or more. However, the problem you run into is in most cases these engines are stock displacement, and in order to generate that kind of power your going to have to turn a lot higher rpm.
1965 Mustang Street Legal Vintage Racer . . .