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A vehicle that has been modified so that it produces a loud, rumbling, aggressive noise when the engine is revved. This modification is known as installing a ‘Grunt Valve’
Dave: Bruv, what was that car that just sped past us, sounded like a TVR or something..?

Joe: Nah mate, saxo.

Dave: Shit man, must have a fat grunt valve innit.

Dave: What you sayin Joe?

Joe Just chillin in the grunt valve innit.

Dave: Fair play, whats the grunt valve sayin?

Grunt Valve: GGRRRRRRR – WAAAAP WAAAAPP WAAAAAAAAAAAAP!

Dave: That’s some serious grunt valve right there Joe, he is on it.

Joe: Innit doe.
by Badmaninnitdoe October 04, 2010
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