Just to answer your point about the power increase it is something like 25PS as you say, however the X--XE V6s were designed for several things - broad torque, to replace the venerable CIH straight6s, economy (I know, doesnt
feel that way but they were) and to suit both FWD and RWD applications.
Variable intake manifold helped the torque curve being nice and flat, economy - managed 40mpg if you sit in top gear at 50ish mph, so pretty good all round, and the unusual 54degree angle of the vees made for a more compact package, it first appeared in the Calibra and Cav. However, everything's a compromise - 170bhp for a 2.5 wasn't much - the legendary 2.0 XE ran 150bhp - replaced with a version that had 136bhp! Vauxhall were directing their engines and engineers towards tree-hugging in the 90s.
I also suspect that a car range featuring a 2.5 with 195bhp, and a 3.0 with 204bhp....may have made buyers squint a bit...and wonder why they should pay more for the 3.0 with as little as NINE bhp...from 500cc more!? Very odd!
1. - Anyone will tell you the 2.5 and 3.0 is 'incomparable' in terms of power/how they feel, so I'm not saying that the 3.0 was pointless, but that this leads us onto the dark world of...
2. - Actual power outputs. So the Cav/Calibra and Omega both have the same engine... except the Omega has a far superior twin port intake system, versus the single butterfly of the former cars (smaller = fits under the Calibra's lower bonnet).. also a different and easier-breathing intake. Now how can they both claim
identical power outputs? Like I say, dark world, and no-one's ever come up with an answer.
That's enough for now, off to the shop!