So I don't know a ton about the diesel VWs, used to race the gassers (late 70s Rabbits or MK 1 Golfs if you prefer) but I know that doesn't translate directly.

My father has expressed an interest in a kit car that uses a Jetta as a donor, with their flagship model utilizing the TDI (much newer than I have nut and bolt experience with).

From what I have read (here and elsewhere) newer is generally better for NVH and power both.

The kit in question ditches the rear seats and re-locates the engine and transaxle to behind the driver and front seat passenger.

Being a retired truck driver he has expressed an interest in the TDI (as opposed to the turboed VR6).

I have ridden in a TDI Jetta ('09 or a '10 IIRC) and the narrowness of the powerband isn't something I expect he will like.

I liked the torque, and I don't expect he would rev it to the moon, but what kind of power improvement would you expect to sustain on one of the newer (commonrail?) TDIs?

Would 200-250 Hp be out of the realm of reason?

Do they maintain the ~2 Lb-Ft / Hp ratio at any level (so 200-250 Hp as 400-500 Lb-Ft)?

In a 2,000-2,300 Lb car I expect that would be more than "enough" ("enough", [eee nuff] the ability to leave two black stripes from any one turn to the next, Mark Donahue).

But would the engine survive (presuming we were able to cool and feed it properly)?

I'm not nearly as worried about the transaxle, axles or hubs, we had to do some "fun" (not really) upgrades on our stuff back when, I'm sure we can reinforce that enough (that and being a retired commercial truck driver, pops isn't hard on gearboxes).

I don't mind having to replace the lift pump, head or main studs, bottom end girdle, performance overhaul, etc; as long as it stays put together after the break in runs.

Or is this a fools errand?

Should I try to track down 3L TDI from a larger VW (Toureg?) instead?

All academic at this point as we both need another project like a hole in the head, but I prefer gathering information before parts.