The Volvo 5 cylinder whiteblock turbo motor came with three types of exhaust manifolds. Part #1270242009 was fitted to 1992-2000 engines. The ‘Japanifold’, part #9207688, was fitted to 2001-2004 engines. The ‘R’ manifold, part #30637921 was fitted to all engines 2004+.
The firing order of the Volvo 5 cylinder engine is 1, 2, 4, 5, 3. This means that with the ‘R’ manifold, exhaust gas pulses from #1 and #2 collide with each other in transit to the turbo. Unlike the ‘R’ manifold, the Japanifold gives cylinder #1 its own runner, which greatly improves exhaust flow. In addition, the Japanifold flows more than the ‘R’ manifold and maintains higher air speed. A Swedespeed user tested the manifolds on a flow bench – you can find the results here: https://www.swedespeed.com/threads/japanifold-vs-r-manifold-vs-early-p80-manifold-w-actual-flow-bench-data.678876/
In our experience, swapping from the ‘R’ manifold to the Japanifold nets an 8% increase in power, just from the manifold swap alone.