1.8 vectra poor MPG (Help)

[ANDYMEATMAN]

hi there my 1.8 Vectra (14k miles) is only doing 21 to the Gallon round town. Not Been Thrashed driven at 30 miles an hour. Filled up on V Power Sheell & done 68 Miles Refilled cost me £16.20. £1.08 litre = £4.75 Gallon 23.5 pence a mile.
Had a Twin Vxr Style Dual exhaust fitted a few weeks a go would this have anything to do with MPG ?
Do you get more BHP with a twin Vxr bak box fitted from the Cat Back?
Any advice Thanks Andy

[merikiito]

thats poor, I get 30-40 depending on usage. Is the airfilter clean? I have a K and N cone type airfilter and dual exhaust as well but I think I have a different 1.8 engine as mine is 2002/3 model 120bhp.

[ANDYMEATMAN]

HI Mate , Not checked air filter will do tommorow raining like hell in
Blackpool. My car is the same as you car 2003 1.8 120 bhp petrol.
The car as only done 14k with full service history from main dealer vauxhall not had her long about 5 weeks and been doing all the mods.

[simac]

My 1.8 rarely drops below 30 MPG, normally get 32 ish. On a run into Wales yesterday it returned 39 according to the comp.

Mines done 65k miles, at just 14k your's could still be losening up LMAO