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Here we see a comparison of the intake port flow capability of the Euro 215 HP S14 cylinder head compared to a new Evo 3 cyl. head w/ the 6 mm stem 3.8L E34 M5 intake valves. The most surprising thing about this chart is how close the two heads are to each other. At least with the factory porting on both heads, going to a larger 38.5 mm intake valve does not produce a huge change in flow at this test pressure. This test was run at 10 inches of water. During the intake cycle the pressure delta across the intake port can get as high as 250 inches of water. Perhaps at such a high pressure the larger intake valve of the Evo 3 cylinder head would allow better flow than the 215 HP head. It is difficult to know for sure as few flow benches can test at such high pressures. But history generally shows that the "shape" of flow charts remains relatively unchanged with changes in test pressure. And the high pressure delta occurs only for a very short time during the intake cycle (it is a pressure spike). So we will have to content ourselves that 10 inches of water is a good "representative" pressure to use. It would be nice to have back to back dyno comparisons with these two heads bolted onto the same engine. Note that there is ample evidence that either of these heads will make more power than the factory 2.3L cylinder head. A future goal will be to flow bench a standard series 2.3L head. Note that beyond 0.400" of valve lift the two ports flow essentially the same. At this high lift value the valve size has little effect, and flow is limited more by the port cross-sectional area. In other words, there is no longer much increase in flow rate for an increase in valve lift beyond 0.400". This indicates that the port is "choked" (this was predicted by the cylinder head technician, based on the small port volume). It is possible that opening up the ports on the Evo 3 head would allow the larger valves to come into play at higher lift. But this would be done at the expense of flow velocity and mid-range torque production might suffer as a result. |
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