US Patent 7150273 Exhaust manifold arrangement

A passageway is provided between branches of a multi-branch exhaust manifold to reduce the amount of backflow (iEGR) into the cylinders at low engine speeds. The passage is located upstream of the turbocharger and can be at the part of the manifold where the branches merge for entry into the turbo. The passageway allows exhaust pressure pulse modulation so that high iEGR levels (using iEGR through delayed exhaust valve closing for example) are avoided. The passage may be controllable to modulate the effect based on engine conditions.