will a4 s4 exhaust fit a8 ?

[Dezzy]

Ok so no it'll be a nightmare to fit. If you look at the 8 one just after the centre box the pipes run to the passenger side of the car at this point you'd need to get those 2 pipes to branch into 4, 2 to go left 2 right. The section that goes to the drivers side has to miss the underside of the car and i doubt that back box will fit.

If you want quad just speak to the specialist and get custom made with tube type boxes to suit.