No need for the spacer if you have the forge dv and an itg intake, as mentioned above, mine was loud enough with that combination. Use to scare cyclists with a little dab of the throttle and lift off
I got a bit tired of it after a while though as it sounded like a rally car and my gf was not impressed, its a bit embarassing driving through town with what sounds like a whistle under your bonnet every time you lift off the throttle.
If your a fan of the engine noise then invest in some uprated engine mounts too.