ok,
if the new exhaust system is 100% there, i.e down pipe to the back box
and it all put together before putting on the car then its a stright forward bolt on job.
if however you have the indevidual parts / sections of the exhuast system then you may require some welding down to connect it all together.
i find its eaiest to fit a new exhaust system when its all assembaled on the floor 'off' the car, then you simply get some help or a stand to rest in on and slide car over it, lift it onto surrport clips (strong, flexible silicon clips work best - i think). bolt on front down pipe, connect lamda senors back up and your done..
However, this is not ganrenteed to resolve all of your problems... there are many things that couse the poor acceraltion and Mpg. it could be a blocked filter - a blocked air filter can reduce air into engine meaning its running on alot of petrol - resutls of this are: sluggish acc and reudced mpg.
also damaged lamda senors may result in poor engine performance...
Best bet is to check all filters & oil levels before forking out alot on a new exhaust system
