Has de-catting my car made increased my mpg

[Lew_C]

Hello everyone,
last week had my car de-catted and coming to fill up this week ive noticed it was cheaper than usual for the amount of miles ive drove.

the price of petrol hasn't changed since last time either and ive been driving it quite hard but the only thing to change is the de-cat exhaust..

i know they are restrictive and performance seems more available and more responsive but i didn't think it would boost mpg

or is this all in my head? (most likely) :homme:

Cheers everyone
:)

[wilsss]

hi ate defo in your head if you said you have been driving it hard aswell i dont think your gunna have a boost on mpg

[Lew_C]

hi ate defo in your head if you said you have been driving it hard aswell i dont think your gunna have a boost on mpg

well thats what i mean, if i was ragging my car why would it cost me less in fuel than before it was de-catted?

[Boyes]

Wierd this mate, mine uses considerably more decatted just wait a few weeks and you might see the difference.

[Lew_C]

Wierd this mate, mine uses considerably more decatted just wait a few weeks and you might see the difference.

could be down to how its been driven, really weird this is. :geek:

[J222JRA]

Im sure Adsayer saw a slight gain in mpg when he de-catted his vts

[Lew_C]

Im sure Adsayer saw a slight gain in mpg when he de-catted his vts

Adsayer is the mpg man ;)
maybe it might then, but yes definitely seems about 3/4 mpg better than last time, i work it out every week too so quite noticeably better over a short period of time.

[Lew_C]

not to mention the old cat looked fubar'd when i took it off too

[luthor1]

outside of the cylinder head *everything* is a restriction.

If you remove a restriction, you'll increase the efficiency of the engine. You are not increasing the BHP of the explosion, you are increasing the % of that power that finds its way to the wheels.

If your cat was particularly blocked, then it would have taken bhp to push the gas out the exhaust, and therefore in any given situation you'd have had your foot fractionally harder on.

Remove the restriction, lift your foot, go the same speed, increase the MPG. Or, go faster for the SAME mpg.

Kind regards

Andy

[Lew_C]

outside of the cylinder head *everything* is a restriction.

If you remove a restriction, you'll increase the efficiency of the engine. You are not increasing the BHP of the explosion, you are increasing the % of that power that finds its way to the wheels.

If your cat was particularly blocked, then it would have taken bhp to push the gas out the exhaust, and therefore in any given situation you'd have had your foot fractionally harder on.

Remove the restriction, lift your foot, go the same speed, increase the MPG. Or, go faster for the SAME mpg.

Kind regards

Andy

Awesome explanation mate, quite simple when you put it like that.
:hug: brilliant

[redlinerdj]

best way to put it ^^

[RustySkull]

Strange, mine hasn't changed since I de-catted it... Just a lot louder haha :)

Merry Christmas Friends :)

[Lew_C]

Strange, mine hasn't changed since I de-catted it... Just a lot louder haha :)

Merry Christmas Friends :)

and you! take it easy mate

[gouldy87]

normally it will use a very small amount more, i noticed no difference at all on my vts

[gaz4399]

outside of the cylinder head *everything* is a restriction.

If you remove a restriction, you'll increase the efficiency of the engine. You are not increasing the BHP of the explosion, you are increasing the % of that power that finds its way to the wheels.

If your cat was particularly blocked, then it would have taken bhp to push the gas out the exhaust, and therefore in any given situation you'd have had your foot fractionally harder on.

Remove the restriction, lift your foot, go the same speed, increase the MPG. Or, go faster for the SAME mpg.

Kind regards

Andy

couldnt get a better response tbh :y:

[steviee90]

yeah it definately increases it, as andy has said....less restriction the less you need to go at the same speed.

[Slugshead]

Definatley made my consumption worse..........

ONLY for the fact I drive in higher revs for the better noise :D

[Tontsy]

luthor1 for de-cat explanation king?!

[adamm]

outside of the cylinder head *everything* is a restriction.

If you remove a restriction, you'll increase the efficiency of the engine. You are not increasing the BHP of the explosion, you are increasing the % of that power that finds its way to the wheels.

If your cat was particularly blocked, then it would have taken bhp to push the gas out the exhaust, and therefore in any given situation you'd have had your foot fractionally harder on.

Remove the restriction, lift your foot, go the same speed, increase the MPG. Or, go faster for the SAME mpg.

Kind regards

Andy

not completely true that surely im no mechanic or nothing but i know it can loose back pressure and slow the car down and use more petrol for instande you take the whole exhaust system off.?? correct me if im rong just thought it can do that.

edit- and before everyone has a go im not saying that rong but surely theres a limit to how much restriction you can take off before you loose a back pressure?

[Slugshead]

not completely true that surely im no mechanic or nothing but i know it can loose back pressure and slow the car down and use more petrol for instande you take the whole exhaust system off.?? correct me if im rong just thought it can do that.


think the backpressure is generated from where the joins are at the manifold, ensuring that the exahust gases have all the same pressure is whats needed to keep is running smooth... or something around about that

[squeaky]

it defo didnt do anything for my fuel consumption she drinks it like there is no 2moz

[adamm]

ohhh so bascily what he said is true upto a certain extent as obviously an exhaust is necisary but a cat isnt. because if you had just the manifold it would sound like a tractor probably perfrom like a tractor and cain the fuel.

[steviee90]

yes, car needs an optimum back pressure, you can run a car with no exhaust but it sounds shit and you lose quite a bit of power, things like cat and silencers create back pressure... removing these reduce it. There is probably a bit to do with bore sizes and stuff... thats why when all these boy racers fit universal exhausts they get shit consumption. As with everything its all about finding the balance.

[Finchowned]

Interesting article on exhausts:

http://microcarproject.tripod.com/html/tuned_exhaust_system.htm.

Perhaps not entirely relevant here but a good read non the less!

[gazthewolf]

good point the engine work s on pulses , very very complicated stuff lol ..... having my one custom made will put a post up on how it worked out . texico fuel seems to last a lot longer in my one ?