are you talking about turbo-jet a/c or turbo prop??
If you firewall the engines on the PW123a (dash8 300) then it costs a hell of a lot of money, as torque can exceed 199%. This means that the engines have to be replaced as it damages the turbine blades. Not so bad on the PW150a (Dash8 Q400) as it is goverened by FADEC and will only give something like 117% of MTOP (don't quote me on the exact figures).
As a turbo-prop driver I could not comment on the effects on by-pass turbofans...
MM
