Thanks for the tip - unfortunately it doesn't look like those will work for the 2015 Subaru. And it turns out I made a mistake when I went to graph the data: it looks like it's actually just one byte governing the tachometer. (My original numbers were all scaled by a factor of 0x9A or something like that)
<pre><code>117 ~= 650 RPM
141 ~= 1450 RPM
174 ~= 2000 RPM
181 ~= 2500 RPM
196 ~= 3050 RPM</code></pre>
I can't seem to find a regression line that both a) reasonably fits this anecdotal evidence and b) extrapolates well to handle higher RPM's.
I may have to revisit the tachometer at a later date/time.
2015 Subaru Outback 3.6R here...
I'm almost 100% certain that 0x0144 contains RPM readings. With the car in park, I slowly revved the engine from its baseline up to about 3,000 five times, resting at idle between each. The last time I was careful to push a bit higher than the others to make sure the pattern was clear.
This pattern is shown by the lower order bytes in the first word of 0x0144.
<img src="http://i.imgur.com/seBbH8H.png" />
Obviously the numbers shown aren't integers representing RPM directly. It's also far too high to be showing 10x the RPM.