Happened across a couple of mentions of success with indexing spark plugs, and wondered whether anyone might have tried it on a Prius. Thinking it might yield an extra horsepower or so, and thought I would give it a go, unless someone's tested it with definite neutral or negative effects. See Indexing Spark Plugs | Advance Auto Parts
I wonder if Prius ICE is using the 'open-end' type of spark-plug (like those in Bosch Platinum 2+ or 4+) where its ground electrodes are not 'blocking' the tip like in the conventional plug. Then indexing will not be a concern.
Indexing is really not important most of the time. The original Honda Insight had indexed plugs; the cylinder head was marked with the correct plug (one of four, A B C D) to use and the plugs were also marked. The Prius OE plug is Denso SK16R11. A guide to Denso code numbers is here. SK = 14mm thread x 16mm spanner, mini-iridium plug (0.7mm centre electrode) 16 = heat range No special reach spec No special shape spec R = With integrated resistor No special electrode shape 11 = Electrode gap 1.1mm (.044")
