What's the secret to retaining good gas mileage in a performance application?

[Unit 5302]

If you want a camshaft, stick with a low duration/high lift scenario. Match your components. Course, you'd be better off going with a turbocharger/centrifugal supercharger setup that is not building a lot of boost below 2500rpm.

Keep your gears in the 3.73's or taller neighborhood. Have the engine dyno tuned to make sure the entire setup is working together properly.

The biggest part of fuel economy was mentioned above. Efficiency. If your engine is running well, you'll get a lot better fuel economy.

Weight is your enemy as well, but lets be honest, there is a limited amount of weight you can pull out of a 4 passenger daily driver without starting to sacrifice your driving experience. The 5.0 engine rocks the house on fuel economy when it's running right. Toss the 4.6L into a lake. I was probably in the 260hp range with my 87GT, and 27-28mpg on the highway was standard.