I wouldn't do too much on them.

The engines are based on Renault but Volvo changed them in every detail, they hired Porsche R&D people to do some finer exhaust manifold, piston and head modifications. The engines are above average, but not as good as a Swedish B23 or one of those..
The engine is not the problem.

Biggest problem is the transmission, they are unmodified Renault trannies that have their bearings shot between 200.000 and 230.000 km. At least, all of the 4 Volvo 440's i know, wrecked their tranny between those km's.

I have a red 1995 440 turbodiesel, i like the engine, it's competitive to petrol cars i meet at the streets, and it does a fine job pulling trailers.
I also like the coachwork and wheel suspension, as it has about 5 cm more ground clearance than average. I live around the forest, and in bumpy dirt roads, nothing beats the Volvo, for the ground clearance and because the long and smooth springs keep a good contact with the bumpy road.
I can climb hills with it, when every upwards meter is about 2 forward meters. Just incredible.

But the biggest problem is the tranny, i bought a tranny from a wreckyard, it was a bad one and i changed it within warranty. Now i have the second tranny from the wreckyard, but this one also has a shot bearing. My 440 is in the barn, tomorrow i will unmount the tranny and have all bearings and synchromesh rings changed at a professional overhaul shop.

You can expect tranny overhauls every 30.000 km if you want to tune it to 170 hp, and use 100% of the horses every day. An ordinary driver will do 200.000 km with it driving carefully. What will happen when you RACE at 150% of the power ??

By the way, did you know that Renault racers tend to use the heavier Volvo clutches, crankshafts and manifolds ?? Dont search for Renault parts, as Renault racers search for Volvo parts. They wont just do that without a reason....