marino_morelli

Back pressure when off boost is desirable to help build boost, then when on boost its designed to open. It comes with an automatic or manual controller so that you can programme it to oopen at a set boost with a manual overide. You'd be a bit of an idiot to drive around at 1.5bar high boost with the valve shut, that's not what its desinged for! You can however vary the opening to reduce the noise. It could be combined with an Ecutek variable map so that at low boost its not particularly loud and doesn't need to be so free flowing, then on high boost it opens up to 113db. At part throttle you can introduce a level of back pressure for quick response and spool which disappears the minute you get proper boost. It's the nuts and can be used effectively if used properly. I think its the ultimate Impreza system, which is why I bought it for my own car, yuo can have the best of all worlds! Motorway cruising without a headache, reduce the volume slightly for trackday limits, have it screaming when you're in the mood. The bypass is 50mm and the centre straight through with the valve is 70mm. So even with the valve only open 40%, you're still getting the same bore as a standard 3" exhaust. So with it fully open its that much less restrictive! The headers are a work of art also and that is an awesome price, these were £1300 new and the Viable £2k back in 2003!!