Originally Posted by lucid
Thanks for the info (135 is indeed heavier than I thought). There is still a difference for both the 135/M3 and M3/M5. Cost is clearly more so. The M3 and the M5 are different in so many other respects as well.
Also, keep in mind that BMW has severely underrated the 135 engine on paper (I don't think the same is true for the M3 engine). My understanding is that it is putting out more like 340hp+ on dyno testing, which would bring the 135 kg/HP ratio to ~4.5.
+1...and +80HP (or more) is a simple chip perhaps exhaust away, so now we are talking 1450/420 = 3.45...assuming they haven't done something like delete the oil cooler, intercooler, etc. that would make that boost level difficult from a temp perspective.