thanks Christian. I too found it for about £200 on the net.
http://www.centrehobbies.co.uk/acatalog/engines_car_os.htmlhttp://www.centrehobbies.co.uk/acata...es_car_os.html
Is more expensive but shows a range of engines. Its interesting to compare them in price and performance to a Magmotor:
._______________|___Mag______|__OS .21 V-R__|
cost____________|___£269_____|___£210_______ |
peak power______|___2234W____|___1875W_____|
weight__________|___1.7kg_____|___0.315kg____|
max revs________|___6000RPM__|___42000RPM__|
peak torque._____|___14Nm_____|___~0.5Nm____|

If the nitro were geared to the same max RPM as the electric it would still only produce a peak torque of 3.5Nm. I think this must be why such light drive-trains can handle such relatively high power in RC cars. It also shows why they have multistage gearboxes.
Mario:I based all my figures on calculations using basic formulas so wouldnt expect them to be too accurate. Ive found a phase diagram for CO2 that basically agrees with what youve said.
Do you have any experience of CO2 being use to power rotary actuaters? Given pnuematic systems high max power to weight ratio they should be good for accelerating a disc.
Mark