U mean the OM447-series the pistons have a short stroke? Cause i
remember engines with longer strokes have higher torque, engines
with shorter stroke have higher RPM. Is that true? 
You're right in saying that an engine with a longer piston
stroke will have more torque and run at lower speeds. The OM
447-series engines have a bore diameter of 128mm and a piston
stroke length of 155mm compared to 122mm x 140mm on a Volvo
9.6-litre engine - hence the difference in piston displacement and
therefore power/torque.
Btw ya, the OM447 has low down torque, cant remember with
version, the engine only has 900Nm, quite low for a 12litre engine
, as compared with 1700Nm for the new 12litre D12E engine from
Volvo. 
You cannot compare engines from different generations. The OM
447 hA engine was developed and marketted for Euro 1. The engine
was turbocharged (without intercooling) and developed what was then
a very high maximum torque output of 900 Nm @ 1000 to 1700 rpm.
What was more impressive about this engine was the fact that it
reached 90% of it's maximum torque at a mere 800 rpm - more than
what can be said about the new Volvo D12/DH12-series engines as
well as the comparitively sluggish Volvo engines of the time.
The OM 447 hA engine was eventually replaced by the OM 447 hLA
turbocharged intercooled engine, although both were sold
side-by-side until the Euro 2 regulations came into force in
Europe. This engine produced an incredible 1100 Nm @ 1000 to 1400
rpm of maximum torque and 1050 Nm @ 800 rpm - that's more than 95%
of peak torque at that engine speed, even though the power curve
was almost identical to the OM 447 hA.
Regards,
Dave
