The problem is with the RS Turbo is that the fuel system relies on every pipe on the inlet and breather to be sealed properly and not split because the vacuum that the engine creates pulls down on the flap under the air filter and inturn, this regulates the fuel. This is how the system knows how much air the engine is drawing.

If you have a split pipe then the engine can suck in air which is not measured by this flap which means more air is entering the engine than there should be fore the amount of fuel entering the engine. A dump valve also introduces an "air leak" into the induction system and can often make the car stall and at best run lumpy. The problem is that the dump valve won't stay shut on idle because the vacuum sucks it open. The only way to get round this is to use a Bailey twin piston dumper or an adjustable one.

Hope that means something to you.