Ryan,
For what it's worth, my Merkur is virtually an SVO with a different wrapper (yet very very different in a lot of ways) and shares the exact same engine. The XR4Ti is actually about 300lbs lighter than the SVOs, and have one of the lowest aerodynamic drag ratings of their time, which you would think all adds up to better mpg...but not really. Mine is still very close to stock and only gets 25mpg which is right at what they're rated at by the factory. Once you start upping the boost and adding toys to it, that number is going to drop. If you were to take a 3.08 equipped 5.0 5 speed and drive it reasonably, you'd be at least 20mpg on the highway so it's really not that huge of a difference. By the time i get mine intercooled and all the supporting goodies needed to run 25psi, it'll probably be around 20mpg itself (although i'll be making 300hp at the wheels compared to the 225hp at the crank of the stock 5.0).
It's all in how you look at it i guess.
Oh and i'll also add....that 300hp might sound awesome, but for the money you can probably have 400hp with a 5.0...that's the reality of having twice the displacement. Also my 2.3 is gonna take a lot more attention than your 5.0 will at the same power levels, so it's going to stay more expensive...which if you can't afford the gas bill for a 5.0 you won't be able to afford the attention to detail bill of a turbo car either.
For what it's worth, my Merkur is virtually an SVO with a different wrapper (yet very very different in a lot of ways) and shares the exact same engine. The XR4Ti is actually about 300lbs lighter than the SVOs, and have one of the lowest aerodynamic drag ratings of their time, which you would think all adds up to better mpg...but not really. Mine is still very close to stock and only gets 25mpg which is right at what they're rated at by the factory. Once you start upping the boost and adding toys to it, that number is going to drop. If you were to take a 3.08 equipped 5.0 5 speed and drive it reasonably, you'd be at least 20mpg on the highway so it's really not that huge of a difference. By the time i get mine intercooled and all the supporting goodies needed to run 25psi, it'll probably be around 20mpg itself (although i'll be making 300hp at the wheels compared to the 225hp at the crank of the stock 5.0).
It's all in how you look at it i guess.
Oh and i'll also add....that 300hp might sound awesome, but for the money you can probably have 400hp with a 5.0...that's the reality of having twice the displacement. Also my 2.3 is gonna take a lot more attention than your 5.0 will at the same power levels, so it's going to stay more expensive...which if you can't afford the gas bill for a 5.0 you won't be able to afford the attention to detail bill of a turbo car either.

