Where have my Horses gone?

[MantaMike]

It seems rather a few of my horses have bolted

I was at an MG rolling road day this morning, and did a power analysis run in my ZT and i'm rather dissapointed with the results..

174bhp @ 6360rpm
160 lb/ft @ 4560rpm

when it should be nearer

187bhp @ 6500rpm
181 lb/ft @ 4000rpm

The car is 5 years old and has done 51k, and is run on Shell Optimax.

I know it is rare for a car to make the manufacturer figures, but i wouldn't expect it to be this much lower, especially as there was a ZS180 there which is the same engine in 180bhp tune and that made 176bhp.

Also the car is due a service in a couple of thousand, but again, i wouldn't expect it to make that much of a significant difference.

Any ideas where my power has gone and how i can get it back!