what simple turbo diesel engine is best?

PSA TDs good but a bit prone to headgasket replacements.

For something simple, reasonably quick, tuneable and ultra reliable I'd be looking at the Isuzu engines found in some Vauxhalls.

Don't dismiss Perkin's fantastic 2.0TD lumps as found in some Maestros and Montegos, but has most will have been scrapped or ripped out and chucked into Landrovers by now.

You could get a Rover L-series diesel instead of the Perkins Prima - hard to find Maestro and Montego donors now with all the Land Rover thievery. It's an updated version of the Prima and found in mid-90s Rovers, and the lower-powered versions are fully mechanically controlled - sounds like you aren't too worried about electrickery and ECUs though.
They are pretty nippy (0-60mph in under 10s when fitted to the Rover 200) and tough.

Most of the Peugeot 2.1TDs you'll find will have the terrible failure-prone Lucas Epic fuel pump.

Thing is, the mechanically controlled pumps are very easy to tweak to that level and above.
You can get the 2.1TD with a mechanical Bosch pump, but only in early XMs and 605s I think.

I´m playing aroound with similar ideas for the van this winter.

Is your van front or rear wheel drive?

also thinking bout fitting one of these. what are the bmw turbo diesel engine like?

blummin heck i'm suprised at the pug diesel following!!!!!

i've heard the bmw 2.5 turbo disels in bmw's & rover 75's are a bit pants! not the best motor bmw have made!

Vote here for the Pug XUD (what a shock). They can blow head gaskets, but only if neglected (old antifreeze/clogged radiator etc.).

I'd go for the 1.9L personally - more common than the 2.1 and not much less power. The 1.9TD does 90bhp as standard. A decent intercooler, more boost and more fuel (both just turning screws) will give it 110bhp easily. Also AFAIK, they are all mechanical, rather than the electronic control fitted to most 2.1L engien, and you're more likely to get a Bosch pump.

The 2.5 isn't an XUD - I think it's the older generation engine fitted to the Pug 505 (which is heavier, less powerful and longitudinal, rather then transverse).

The XUD was converted into an aircraft engine, and the time between overhauls is the longest of any piston aircraft engine at 12,000 hours. R-R Merlin engines need a rebuild evern 500 hours, I think. Lycomings etc need rebuild every 1000-2000 hours. It's very common for the XUD to cover 300,000 miles without trouble. It will easily cruise at 80mph, returngin decent MPG while it does it.

What van is it going in? The size and weight will make a big difference to the final fuel consumption.

XUD 1.9, bosch fuel pump, oily but incedible. Last 306 d-turbo I had was bloody fast at 130,000 miles and on country roads you can't beat murdering the environment with thick black overfuelled fury.

Another vote for then Pug lump here
TBH i've had more Isuzu engines in with H/G problems than Pug lumps but again it's ni-on allways down to lack of antifreeze/maintenance .