You need roughly 250-270 crank horsepower to hit 150 mph depending on frontal area and drag coefficient.
To hit it in 4th with a T5 you'd need to spin the engine to at least 6500 rpms with a 3.27 rear gear, over 8000 rpms with 4.10's.
The 5.0 design is good, but from the factory it just wasn't designed to make the kind of power a Z06 can put down. With a stronger block, heads and cam designed to rev, and 3.73 gears, it could hit 150 mph in 4th if it can rev to 7500, and that's possible. But the level of power it needs to make to be faster than a Z06 just in a 1/4 mile requires more than just heads and cam. Displacement is king for a reason. Turbos and superchargers increase the effective displacement, but you still have the problem of rpms and rear gear.
I'm not saying it's not possible, I'm saying I don't think I've ever personally seen a 5 liter fox body actually capable of doing it,
maybe on a trailer but certainly never driven on a city street even on a weekend. Despite what you hear on a weekend standing around a parking lot.
It's a fine car even if it can't beat a Z06 or hit 150 mph in 4th. I'd just smile and nod unless I owned a Z06. Then I'd want to race
