[quote author=forester sti link=topic=16604.msg204035#msg204035 date=1248255668]
[quote author=Dagnut link=topic=16604.msg203845#msg203845 date=1248211649]
There was great system from aus the basically provide to routes for your exhaust one was through a cat and a silencer the other straight through..simply flick a swtich and a control flap opens up the loud route..cant remember the name of it but would be perfect for most of us especially dealing with nct..I would say thats how they will target loud exhausts decibel test at the centre
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That sounds perfect!
The butterfly valve at the top would defo be a restriction at high bhp levels
Dan
[/quote]
There is a butterfly valve is in the exhaust either way. The apexi one just restricts the flow, and the one dave is on about redirects it by blocking the main pipe. Just means you cant drive her on with the apexi one near closed, but when they are both open there is still the valve in the exhaust so same effect at max performance