car drinking petrol after changing exhaust?

[AdamDougal]

i changed my twin exit exhaust with a cat on it for a straight through decat standard pipe from the manifold connector to back box,
now all of a suden im geting rubbish MPG?
anyone help me out as im lost here?
i have no idea what could be the problem as i have no idea about exhaust problems etc.

help would be great thanks.

[Lewiswhitlock]

Lose the cat lose the mpg, keep the cat keep the mpg. Well i believe thats the common way it works? Correct me if wrong someone

[Lew_C]

Originally Posted by AdamDougal

i changed my twin exit exhaust with a cat on it for a straight through decat standard pipe from the manifold connector to back box,
now all of a suden im geting rubbish MPG?
anyone help me out as im lost here?
i have no idea what could be the problem as i have no idea about exhaust problems etc.

help would be great thanks.

is it a mk1 or mk2? you havent left out a lambda sensor blank or something have you? doubt it though it should be in the manifold.. strange one. my car was a tiny bit better on fuel after de cat cuz its less restrictive but i hooned around more so it drank the fuel lol x

[AdamDougal]

Its a mark 1 but mark2 exhaust?:/ weired i know lol
And the lambda sensor i have no clue? Lol

[montsta1]

i found the same thing mate, my decat lost me a few mpg, but the sound make up fr it

[stevyj]

sponds better decat didnt notice that much difference in mpg get 35 to 40mpg staedy away. make sure lamdas connected and no blowing on joints

[Steve]

i got better mpg with a de-cat.

You not rev'ing it driving it harder to hear the exhaust more lol?

[atspeedracing]

the problem is usually because people drive different because they like the sound of the exhaust.

the ecu doesnt know what exhaust you have, so doesnt change anything.

if the engine is breathing better, you should be able to apply the same power, with less throttle.... but as i say, people usually apply more throttle because they like the sound lol.

- colin.

[geoffgti88]

I didnt notice a change in mpg, but did notice that it sounded more sexual (well in my opinion) lol

[Boyes]

Possibly blowing?

[Liam_]

Originally Posted by Steve

i got better mpg with a de-cat.

Ditto - both my Saxos have been the same. Can't understand how people often experience the opposite haha.

Check stuff like tyre pressures, give the car a service if it hasn't been done in a while etc.

[Barry123]

It'll be the increased-noise-effect. Basically the decat makes the car sound meatier and you're probably giving it some more often that you realise.

Secondly the decat is going to make the car run a touch richer for the first couple of hundred miles whilst the ECU adjusts the fuel trims to suit the adjustment in back pressure.

decat should give you a bit more mpg if you behave yourself with the right foot.

[bibbles]

well, do u stick to a certain gear-change @ specific rev, for instance, every time my rev's reach 1.5, i change gear, up until im at 30mph in 5th. i get 80 miles out of a tenner, with the total excellium gear, which is roughly 54mpg. so maybe it could be something completely irrelevent. have u checked the tyre pressure recently? im mad for MPG and this is usually the cause. 0-60 in 9.35sec and top speed 117 my little sexo VTR OH BTW i have no CAT and i have a shitty standard £100 exhaust jobby while i wait for my powerflow to be fitted x

[Cammy]

Hmm, i used to get quite good MPG with my Mani + milltek on, full tank would do me about 400 miles doing long runs... but i sat at 60 the whole way as allot of my driving was up north and back most nights.

[rorz_vts]

Originally Posted by bibbles

well, do u stick to a certain gear-change @ specific rev, for instance, every time my rev's reach 1.5, i change gear, up until im at 30mph in 5th. i get 80 miles out of a tenner, with the total excellium gear, which is roughly 54mpg. so maybe it could be something completely irrelevent. have u checked the tyre pressure recently? im mad for MPG and this is usually the cause. 0-60 in 9.35sec and top speed 117 my little sexo VTR OH BTW i have no CAT and i have a shitty standard £100 exhaust jobby while i wait for my powerflow to be fitted x

30 in 5th wouldnt that be puttin strain on the engine/box

[AdamDougal]

thats what i thought lmaoooo

[Gareth_R]

anything less than 30 does, but 30 in 5th is fine

[axsaxoman]

reasons simple --presuming driving is same
you removed cat and now have no box where cat was --Iam guessing no centre box at all .
the placing of the cat /first silencer -expansion box is important ,as that is the tuned length of the exhaust --so by removing the cat and having no box you have lost torque
making a tuned system is all about the primary +secondary lengths up to the FIRST box --after that as long as it is not smaller it makes little difference as long as its not smaller dfia
-,I am guessing it also makes a "bumming noise at around 3-4k if you have no center box --then goes quieter above + below that rpm band

you have screwed up the tuned length and therefore lost efficency

[stedixon]

i used 2 gett good mpg on the vts bu fuked dowt with it tht muck im lucky to get 20 mpg now