Most available aftermarket performance parts are only available for the P11 heads. The P12 heads uses different valve springs, retainers, guides, seals, valves etc. The exhaust ports are exactly the same on both P11 and P12 vs the intake is slightly different in port dimensions and bolt on locations.
The main difference that would make the P12 head "flow" better is that it uses a smaller diameter valve stem 5.5mm vs most SR's that use 6mm.
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