Thinking of purchasing a Haltech ECU and diesel turbo for the 1.9 in my T3. Interested in people's thoughts.

your 1.9 is a diesel? If not then the turbo will quickly overheat as they are constructed differently to a petrol engine turbo.

Going for an ECU is a good idea so long as for a minimum you use a crank trigger and MAP sensor. This will at least make full use of a mappable ignition curve for engine load relative to engine speed. Going fuel injection will of course give you the best power as well as MPG.

A well thought out system could pay for itself within 4-5 years too

I can't offer much of an opinion on which ECU to use, because I don't have any experience there, I have always just used piggybacks on a factory system.

Turbos however, the hardest thing is to try and match the boost level with the performance curve and the engine capacity. A 1.9 petrol engine that makes peak torque near 3000 stock and peak power at 4500 will likely use one of the modern diesel turbos very well, but they use a lot of boost generally, so you may have to tame it down a bit.

This website is just the best thing in the world for this type of matching. It has heaps of compressor maps, and you can change engine characteristics for the real world and get a repeatable output.
http://www.squirrelpf.com/turbocalc/ 

I used a 1.9L motor, with target HP pk of 175 @ 5000, TQ pk @ 3500, redline @ 5500, BSFC of 0.5, and pressure reference of 14.0:1. I didn't use an intercooler, so no losses (that's a personal thing, I would use a 2-stage spray instead).
When I plugged in the turbo map from a K03-2072, which is very very close to the K-series turbos used on both the 1.6L Citroen HDi I used to have and also the 1.9L TDi VW, the map suited it beautifully.

Have fun.

PS: OH, and I rekn these people might have what you want for a decent price.
http://stores.ebay.com.au/High-Performance-Turbos/VW-Audi-Turbos-/_i.html?_fs...

Thanks modnrod and psimitar

Oh and as I'm not sure if you're using mechanical or electronic injection then be warned that tuning a mech diesel injector pump is a pretty specialised affair.

Elec injection is far easier and cheaper to tune.

Psimitar I am running a petrol with efi

Cool Well then as ModnRod has said you'll be looking at something similar to an Audi/VW 1.6 TSI KK03 turbo but would need to look thru the different turbos compressor charts to see where the sweet spot lies as at an educated guess the 1.6 will be a better fit for your 1.9 due to the lower RPM available compared to the RPM available to a 1.9 TSI.

You may even have to go 1.4TSI to compensate for the flat 4s compression ratio.

Either way it's a fun subject to get your noodle in a twist