Originally Posted by Dessauer
The JTD is a 120bhp 8v SOHC engine.
http://pictures.autotrader.co.uk/img...a?id=671931306
The JTDm includes an 8v 120bhp version (available in pre and post facelift models), a 16v 140bhp (pre-facelift) DOHC version and a 16v 150bhp (post facelift) 16v DOHC version.
http://picnic.ciao.com/uk/8582742.jpg
http://pictures.autotrader.co.uk/img...a?id=679469910
All are common rail direct injection diesel engines but the JTDm (red m-jet badge on the rear boot lid, and in the case of the 16v, additional 16v letters on rear boot lid and engine cover - see above picture) has uprated injectors which operate at a higher pressure than those in the earlier non-m JTD. The 8v JTDm engines never reached the UK though.
There's also a 16v 170bhp version of the 1.9 JTDm engine scheduled for inclusion in the Ducati version of the 147

All correct, but this is on a 147. This thread is about the differences between the JTD and JTDm engines fitted to the GT. Yes, there are more variants fitted to the 147, there's also other variants in the Vauxhall Astra, Vectra, Saab 9-3 and Saab 9-5.