Originally Posted by HUMBER P4VWL
DHD - RE the 135, 150 and 175 block, it is my understanding they are all the 2.5L V6 engine. Or do you mean three is a slight difference in the block, perhaps bored out or something as well as a different ECU? I'm curious now. The 175 was always priced a lot higher than the 150.
The 135, 150 & 175 are all 2.5 litre V6 blocks, but the 175 is physically different (I'm not sure to what degree), so it isn't simply a matter of changing the ECU to convert a 135/150 to 175hp. I'm not sure what, if any, hp increase would be achieved by fitting a 175 ECU to a 135 or 150 Opti. If you lob your ECU in the post to me, I could give it a few test runs on the river to find out?
AFAIK, upgrading a 135 Opti to 150hp only involves an ECU swap, but the 135 lower unit has a different ratio to the 150, not that this has any bearing on horsepower.