Hi! Glad to be here!
My boat is a Bayliner 2550 cruiser. The old engine was an OMC 5.7L (260hp) with an OMC Cobra leg single prop.
Yes, repowering a 20yr boat with a "hi-tech" engine package was a tough decision at first but the hull was in mint condition and I wanted reliable power plant for a number of years to come so that's what I did.
Volvo EVC stands for Electronic Vessel Control, EC stands for Electronic Control vs MC - Manual Control.
The repower was quite painless. No problems or issues. The only thing that had to be done at the transom was a couple of extra bolt holes drilled for the transom plate. Other then that it was plug and play.
PTA (Power Trim Assist) is a software "add-on" to the standard EVC/EC system, I didn't know much about it at first and luckily my engine actually came with it.
PTA automatically trims your leg depending on engine RPMs. It's only RPM based, boat angle isn't factored in.
There are 5 different settings that can be customized.
You can manually override the trim settings at anytime and you can turn PTA off completely, but you really would never want to. With PTA you get on plane much faster, and just generally find you have overall better boat control when slowing down and speeding up. With this system you never have to trim the leg, only time I've touched the controls was to lift the leg when coming close to a beach. I find on this Bayliner hull it's a day and night difference with PTA on or off.
Some of the other things you notice with EVC are "smoothness", every action performed with the engine/leg is done with precision. Shift into gear and it's always the same predictable motion. Push the throttle and it's always a smooth acceleration to whatever RPM you want, and the engine will sit at that RPM regardless of conditions. The computer adjusts the fuel flow to always maintain the RPM. You can't easily make a mistake, if you were to move your throttle/shifter from WOT to reverse in an instant, the computer would slow the engine down appropriately, shift to neutral, then to reverse and apply the gas....all without user intervention. It may sound like you are giving up some control but once you've tried it, manual controls seem outdated. :-)
I am very pleased with the EVC system. The price between the electronic throttle/shifter vs the manual was virtually identical....but many dealers were not familiar with it.