Here's the breakdown:
ECODiesel (1991-1992 USA only):
1.6 liter motor
Hydraulic lifters
Turbo (K14 usually) with mechanical wastegate
Catalytic converter (tiny)
Injection pump is NON-compensating (i.e. lacks the LDA boost aneroid on
the top of the pump which delivers more fuel under boost.)
Dual fan setup with 3-speed fans (run by relays and fan temp switch).
Originally mated the the AVX transmission which has RARE 4.25 final drive
Standard 1.6TD (1982-1986)
1.6 liter motor
Mechanical lifters
Turbo (K14, but also Garret T2 or T3)
Straight exhaust
Boost-compensating injection pump:alters fuel ratio under boost
Single fan with 2 speeds
If you have an ECODiesel and want more power, the pump is a quick way to do it. It's plug and play, but you'll have to run a hose to the intake manifold for the boost aneroid. Used injection pumps (for the early TD) turn up on ebay all the time. Figure you'll have to get it rebuilt if you buy a used one. Make sure you GET part numbers off the pump to make sure you don't buy a late (1988-1992) 1.6NA injection pump with the altitude aneroid on the top: it looks the same as the earlier 1.6TD boost aneroid (LDA). I'm not cetain of the part numbers, but perhaps someone here can chime in. If you get a used pump in need of a rebuild, you may have Giles do one of his rebuild mods to it (not sure what he does, but everyone loves it despite the cost).
If you have an ECODiesel and want to put on the earlier injection pump, you may want to hollow out the cat. With the added fuel under boost, you may get excessive particulates that may clog the cat. Just an idea.
This forum is a great place to find out about IDI mods. I'm sure at least another 1/2 dozen people will chime in with cheap power mods.
For more info on the ECODiesel and it's history, check out this webpage. But be sure to turn down your computer volume so you don't have to listen to the goofy music.
http://www.geocities.com/vwecodiesel/