The dyno of choice in the US is a Dynojet brand. Over here, it's Dyno Dynamics. Both give a significant difference in horsepower as measured at the tyres. This page explains it all
http://www.twinturbov8.com/dynostuff.htm
If you hear of the "Mustang" brand of dyno used in the US, that's the dyno that will give the same results as our Dyno Dynamics version.