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One thing I want to ask on, and this is something as a result of messing with the older reverse intake manifold design on the series 2 boxer engines (ej251,253) is flow
I had a bolt on 2.5RS with an "extrude honed" intake manifold but I had told the shop (bonehead performance) to pay less attention to port matching it with the gaskets and more on flow numbers to try to balance flow at a given cfm.
typically all generations of the series 2 boxer had issues with cyl number 4 running lean due to intake design, and that was the limiting cylinder for making power both NA and boosted.
One tuner in washington swore up and down I had thrown cams in my 251 and didnt tell him since the flow numbers and his "off the shelf" tunes didnt work as a base for my engine. I eventually told him it was the intake spacer and flow match porting I had done with an equal length exhaust header with a 18 inch merge point. ( TWE is the brand that did most of the bolt on stuff for NA subaru engines)
So this is what I wanted to query on. Could you test the flow numbers per runner and modify your intake design based on that? Also changing running lengths and angle too?
an old hot rodding trick was to involve a dual plane runner so left bank and right bank cylingers where drawing from different "volumn pools" while running ( I forget the split but air going into one cylinder wouldnt have to be sucked into the next cylinders intake cycle.
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