The old Mustang dyno we used was about 15% lower than a Dynojet - we know that because the same car was taken from that dyno to all the local dynos to check on that. But, one thing to keep in mind with a Mustang dyno - and to some extent with a Dynojet, the operator can play games with some of the settings so a Mustang dyno can actually give higher numbers than a Dynojet.
The new dyno here is a brand new Dynojet - I like them SO much better than any other dyno and we've used probably all of them. The software is a lot better.