Thanks @opasha, it is deeper tone. It makes the car sounds like the real 6 cylinder car.
I'll try my SLR in the next couple day. Going to track the truck tomorrow for my local dealer track day event.
I want to see how many people going to think that I'm crazy tracking this truck.
But, since it is a turbo car, at high rpm, the sound is almost like stock.
Can't wait for the catless downpipe, it should bring the sound more.