He's probaly just scared you will out run him after you get it tuned!

 

it doesnt matter if its old new, or whatever....anything can blow on a dyno. all it takes is one weak link. some have em some dont. gotta risk it to find out. i imagine that ta 120k miles...the car has seen a WOT run or two...so id say it can handle it. if it blows...then you were not that far from doing it off the dyno anyways......take the car to be tuned elsewhere also. that guys a ***.

 

I say put it on the dyno, then take him for a ride afterward, make sure you call him a idiot in the process.