My tuner says you can't get much more

[AlloyPony]

There is a shop about 20 miles from me that we all take our Mustangs to for dyno tuning. He's a former Ford mechanic who went out on his own to focus on performance for Ford vehicles. He tuned my bolt-on 2001 GT and got 40 HP and 50 lbs/ft of torque out of it. I was shocked. He does really good work and people come from other states to have him do their cars.

My father was talking to him yesterday about doing some work on his GT500 and while they were chatting he mentioned to the tuner that I have picked up a Mach 1 that I'd like to get tuned soon. The tuner told him that on the Mach 1, there isn't much gain to be had. He claims that on these specific cars, the tune that Ford used is really good and is pretty much at the limits already. He said there might be 3-5 HP to squeeze out, but without doing headers and more serious mods, there isn't much that you can add to the tune itself.

Have you guys been told this by your tuners? I want to keep this car closer to stock, so if 3-5 HP is all that's left on the table, I'm not going to spend the $450.