Here's what I've found on 2.2 diesel tuning:
Chiptuning Direct £244 26% increase in power & torque ‘Fools’ ecu into upping the common rail pressure.
Tdi Tuning store £235 Power increased to 160 Bhp As above
P-Tronic £419 26% increase in power & torque As above
Racechip.de €129 +27% power & +20% torque. As above
Racechip.de €179 +31% power & +26% torque. As above
Diesel Power Tuning £300 +20% power & + 19% torque As above
(160 bhp & 280lb/ft)
Celtic tuning £306 +31% power & +30% torque Involves re-map of ecu software – they come to you, 14 day money-back guarantee
(178 bhp & 305lb/ft)
Torque Cars £??? +41% power & +40% torque Technique unknown
(192 bhp @ 4150 RPM & 329lb/ft @ 2250 RPM)
Superchips £499 +26% power & + 36% torque Re-map
(172 bhp @ 3520 RPM & 320 lb/ft @ 2450 RPM)
No doubt there's other options out there too. The first group 'modify' the MAP sensor signal causing ecu to increase common rail pressure therby injecting more fuel than it expects. Two thoughts:
1. Bad news for HP pump, constantly straining beyond design limits?
2. Could you do the same thing with a resistor for 5p?
I feel altering the injection duration(s) is the better way to go, but it's expensive.
All options offer little, if any, improvement below 2000 RPM, which is where the 136 is least impressive. The std lump goes really well from say 2250 - 4000 RPM, you just need to keep it spinning a bit more than feels entirely natural.
Anyody got a twin turbo 170 BHP 2.2 they don't want?
), there's a few testimonials but they don't say anything you don't already know. There's also stuff from real people who are still happy many thousands of miles onwards, have a squint on this here forum thread, a couple of happy customers. 
