hey Sholin.
Sorry for any misunderstanding here - all the anacronyms are confusing!
I'm sure I've posted on this before but couldn't find it in the search so (don't worry, I enjoy it
).:
VWs old 90bhp and 110bhp (with variable vane turbo) units are TDis - mechanical pump.
Then they had TDI (PD) 115bhp. Now replaced with 100bhp and 130bhp units. Then 150bhp unit. All still 1.9l with 2 valves/cyl.
These are a high pressure system - like common rail (=CDI) - but without a common rail and instead using an ultra high pressure (30,000 psi) pump - Pump Duse or PD. (vs. 23,500 psi for common rail).
From
http://www.tiscali.co.uk/motoring/roadtests/2002/05/03/story_1.html
"The turbo-diesel, direct-injection (TDi) engine is now quite familiar, but what about the PD bit? PD stands for 'Pumpe Duse' and translates as 'unit injector' - a device that supplants the old distribution pump as the source of back-pressure at the injector nozzle. In effect, PD injectors each have their own little cam-operated pump to produce even higher pressure (30,000 psi) than a common rail system, which uses a thin, tubular reservoir to contain pressurised fuel for feeding on demand to each of the injectors in turn.
The higher the pressure, the more effective and leaner becomes the upper-cylinder burn. Consequently unit injectors (PD) produce more power and torque for a given measure of fuel without cost to fuel consumption and CO2 emissions. As an example, the 130 bhp TDi PD engine in the test car, for the same 1.9 litres as the TDi unit it replaces, generates 13 per cent more power (130 bhp) and nine percent more torque yet returns an identical 52.3 mpg on the combined cycle.
The known facts are:
PD
+ More powerful
Common Rail
+ Quieter
+ Is catching up, though now on it's.. 3rd version?
To drive, I've only driven BMWs 320d 150bhp Common rail. It's quite petrol like, but in a way that actually makes the engine not that lovely. It needs revs somewhat and doesn't have the huge low-down kick that is the nicest feature of turbo diesels.
VWs PD's I've driven a number of. They have great low down punch from 1500 rpm, and don't drop off at high rpms like old TDs. Feel so superior to normal TDIs. And, rarely for a turbo diesel, very nice combined with an Automatic. Fast when fitted in a Golf.
Only VW develops PD (believing it is superior). Technically they are quite possibly right, but with more manufacturers backing common rail, they have competition.
N.B. all VW engines available in Audis too. A8 4.0 is the fastest diesel you can buy (275bhp, 0-60 6.7s, 155mph max limited). Oddly, this runs common rail not PD.
N.B. VW now has a 2.0 4 valves/cylinder PD. They haven't made a high output version yet, but it may replace the 1.9 TDi 150bhp as the highest specific output diesel available.
wow. that was long.
So in short, TD is elderly, no-longer with us and clearly inferior to modern PD and CDI systems.
Russ