Well actually, my 'home' track actually pretty much only requires an engine that runs well! No need for high end power or efficiency, as long as it moves the car and lasts 6 mins it is good enough to win as long as the car is setup right.
I had a modified JLR Red Dot, and that thing was ballistic!! ...well, when it was working
Even the stock JLR was powerful as hell! Kept up with Nova's and caught up to them in the straight - meaning A LOT faster speed at the end!
Now I have an unmodified RB T10 (as it says in my sig) and that runs extremely well, and now that my car is very close to an optimal setup, I know it can be the fastest at my track, I just have to work the corners better and get a little more rear grip.
All engine modders are good, and it can depend on how much you are willing to spend and how long you want to wait. If it's local, go for it, but be certain he knows what he is doing.