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subaru performance
subaru performance  

Subaru cylinder head porting and combustion chamber modification

The exhaust ports are actually designed to flow less at low lifts. This is to balance the low lift flow between the intake and exhaust, (it should be about 77% to 80% of intake flow), and to reduce excess scavenging at the exhaust during valve overlap (intake, just closing and exhaust, just opening).

*NOTE: All of our flow bench testing is performed before the multi-angle valve seat cut is performed. This ensures that we are comparing the flow of the ports, not the valve seat cut and radius. As stated in the valve seat machining section, a proper selection of angles and widths for the valve seats can contribute to as much as a 10% gain in total flow in a modern four valve head.

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