Thats why I have on mine, and I'm very happy with it. It CAN be quiet, like 1500rpm and lower, but get it to 2500rpm and up and thats when it really starts to scream over the catted X I did have on my car. Do you know which 40's he has? Originals or the super 40's? The super 40's I have are supposed to have lower resonance inside, and I must say that the ride is very quiet inside compared to outside.
Basically just tell him its very deep, very loud (not the loudest possible, but loud), and he should like it.