… thinking about STOCK intake manifold and its pressure in time running

- the higher the restriction in the Y (MAP-sensor-position), the higher the pressure delta between Y and the imf
- the restriction in the Y in stock version is high, when only one cylinder is fed - and relatively low, when 2 are fed
- when a inlet valve opens (the restriction decreases instantly), the pressure in the imf peaks for a moment
- when a inlet valve closes – the opposite happens

 

… in a absolute stock car this might be fine because the restriction not only in the imf is high but also in exhaust. This might work well together in stock.

BUT the fact is – the pressure peak in imf is during valve overlap – so you might a lose a bit air mass if your car has already lower exhaust restrictions.

 

… with a high flow exhaust system you reduce backpressure of the exhaust (my models says by 3 psi). So the pressure difference between boost and backpressure is this amount higher - … so you might lose a bit air mass more.

When you implement crossovers to your imf – you equalize the pressure in time running – there will be no peak anymore. So the pressure difference when the inlet valve opens is like in stock system again – nice effect - … so the cylinder filling should be higher – and you gain even more with your high flow exhaust system.