Gday all.

I'm just wondering if its possible to get a decent exhaust without having excess noise? My car is currently using about 12-13L/100km which is about 1-2L more than it used too.... I'm not driving any differently than I have in the past and I just can't seem to get it below 12 without sitting on the freeway for a while.....I've been advised that a more free flowing exhaust would lower fuel a bit....

Background info - if it helps:
- Car has been recently serviced - spark plugs changed, timing belt, oil etc everything done about 2000k's ago
- I have placed on some 18" rims with 235/45 tyres - would that account for the increase in fuel usage?
- Car has been sitting mostly unused for a good few months - maybe I need to flush out the oil and replace the filter?

What our thoughts on the issue and if a better free flowing exhaust would help much? (if it does what the recommendations for ones that AREN'T noisy)

Cheers folks - TheKovac

Id change the O2 sensor, really high flowing exhaust wont give you any difference, well at least it didnt in my case. I have large wheels as well with 235/45 & i didn't notice any difference in consumption when they were installed. Any how when my consumption increased it was lazy O2 sensor, will cost you about $150 to get done with genuine one. Id say its really the only thing left since you did you major service just recently.

If the car has been sitting for so long perhaps a new oxy sensor and a good injector flush would assist not to mention fresh fuel as I am sure the fuel will be going stale also

I also keep genuine oxy sensors on the shelf here

Cheers for the replies guy - appreciate it heaps....


Id change the O2 sensor, really high flowing exhaust wont give you any difference, well at least it didnt in my case. I have large wheels as well with 235/45 & i didn't notice any difference in consumption when they were installed. Any how when my consumption increased it was lazy O2 sensor, will cost you about $150 to get done with genuine one. Id say its really the only thing left since you did you major service just recently.


If the car has been sitting for so long perhaps a new oxy sensor and a good injector flush would assist not to mention fresh fuel as I am sure the fuel will be going stale also

I also keep genuine oxy sensors on the shelf here

Seems the verdict is the oxy sensors. Is there anyway to definitively determine if the oxy sensor is at fault? $150 is a bit of an expense and I hate to have wasted my money if that wasn't the issue.

Also I suppose apart from pissing my neighbours off and getting more attention from the cops - a free flowing exhaust will do nothing I'm guessing?

As you recommended Mal I will do a good injector clean - anything else I should replace - i.e. filter/oils? I've gone through about 2 tanks worth of fuel so I pretty sure that is fine. My coolant is a little old so I think I'll buy some genuine coolant and do a full flush as well.

So the extra fuel usage wouldn't be from the wheels then? I did a read a thread or two that mentioned that due to having more tyre on the road combined with the extra weight of the wheels would increase fuel usage. I just wasn't sure if that would 2L's worth per 100km.

Wheels would make a difference if they weigh more, but 2L on top of 10L / 100km is a 20% change, that's not likely at all.

I've found that exhaust and intake mods on a previous car did improve fuel economy. If you don't have a Sports / VRX model, consider swapping in one of those mufflers. They are reasonably quiet and free flowing, giving some extra power to the car.
If a mod doesn't cause more fuel or air to be pumped into the engine but produces more power, then you've just improved the efficiency and hopefully would improve fuel economy too.

But it does sound like something else is odd.

Does the fuel usage change coincide with the service? Did they use the wrong type or too much oil? I'm thinking that a really thick oil would sap power from the engine, needing more fuel to travel the same distance.

Something to look at before O2 sensor maybe.

Oh yeah, compare the new tyre rolling diameter to the old one - if they are a bit smaller, this will make your speedo read less kms travelled, and therefore you'll be using more fuel to travel each 100kms, but you'll really be travelling about 102kms - so that would account for a small %age of increased fuel. If the wheels are heavy, there might be another 2% there. Still a long way to 20% difference, isn't it!
Check your air filter, make sure it's not totally blocked up :)

Kovac, if you are worried about money, factory coolant is not the way to go, you are buying a 5l bottle which is 66% water, not real good way to go

The Injector clean will cost you $150 for it to be done here, the Oxy sensor is $135 if you want to install it genuine.

Coolant will not change fuel economy however and the amount of change you will get with an free flowing exhaust would not account for the amout you claim to be using either unless it is blocked which given it sat for almost a year could I guess be possible

You can test out the oxy sensor before changing it, Correct me if im wrong on this one, basically if its being "lazy" (slow) to send adjusted signal when engine load changes its getting old & needs to be replaced. Thing is some will charge you like $50-$70 just to hook up & check.....

Kovac, if you are worried about money, factory coolant is not the way to go, you are buying a 5l bottle which is 66% water, not real good way to go

The Injector clean will cost you $150 for it to be done here, the Oxy sensor is $135 if you want to install it genuine.

Coolant will not change fuel economy however and the amount of change you will get with an free flowing exhaust would not account for the amout you claim to be using either unless it is blocked which given it sat for almost a year could I guess be possible

I agree the factory coolant isn't great value for money if you buy it ouright. From memory its around $50 RRP. I do have a mate that works at mitsubishi and he can get me for about $25 - in which case its pretty good value. I've been recommeneded to buy it because it has a bit of wax in it that lubricates the lines and coats the lines a bit. If I wasn't going to get genuine - what would be your recommendation?

The car was used during the last year - it just wasn't used often... about 1 or 2 a month we made an effort to take it out for a bit of a drive but nothing major......is fuel the only telltale sign of the injectors being blocked? Performance wise the car is great - very responsive and smooth - with the new plugs its better than it was a few months ago....the only thing with the car is when its cold the idle is a little bit rough to the point where it shaking my rear vision mirror quite nosily - although after a few minutes of driving its fine....

Cheers for the prices - I'll probably be in contact soon about them. Just got to find some time as I've currently got uni exams.


Wheels would make a difference if they weigh more, but 2L on top of 10L / 100km is a 20% change, that's not likely at all.

I've found that exhaust and intake mods on a previous car did improve fuel economy. If you don't have a Sports / VRX model, consider swapping in one of those mufflers. They are reasonably quiet and free flowing, giving some extra power to the car.
If a mod doesn't cause more fuel or air to be pumped into the engine but produces more power, then you've just improved the efficiency and hopefully would improve fuel economy too.

But it does sound like something else is odd.

Does the fuel usage change coincide with the service? Did they use the wrong type or too much oil? I'm thinking that a really thick oil would sap power from the engine, needing more fuel to travel the same distance.

Something to look at before O2 sensor maybe.

I will look into the VRX muffler. I got to try and find one first but I have heard that the noise from it is quite bareable. I've just got to first convince the parents - which is no easy task! They're quite against me getting an exhaust system....

I'm going to take my car to my mechanic for him to look at a knocking noise from my front wheel and I'll get him to do bit of a check through the engine to see what he can find...

Appreciate the help everyone :)

lol @ your parents kicking up a stink about a VRX muffler, I can fart louder then one of those, wait until you actually get an aftermarket system or a cannon and THEN hear them complain. VRX muffler is quiet as dude.

Also, your like 20 years old, and its your own car, if they dont like you getting a factory sports muffler for your car, big deal! what are they going to do? Remove it? lol

;1331194']lol @ your parents kicking up a stink about a VRX muffler, I can fart louder then one of those, wait until you actually get an aftermarket system or a cannon and THEN hear them complain. VRX muffler is quiet as dude.

Also, your like 20 years old, and its your own car, if they dont like you getting a factory sports muffler for your car, big deal! what are they going to do? Remove it? lol

LOL Yeah you obviously don't know its like to have wog parents! You cannot give them attitude like "what are you going to do about it" because they will do something about it! .... They'll probs make me park like 1km from home or something lol ....trust me they have their ways - I'm kinda under their roof so yeah need to sort of work with them........VRX muffler sounds like a good compromise - fix the car up a little and then I'll start scouring wreckers to find one...

LOL Yeah you obviously don't know its like to have wog parents! You cannot give them attitude like "what are you going to do about it" because they will do something about it! .... They'll probs make me park like 1km from home or something lol ....trust me they have their ways - I'm kinda under their roof so yeah need to sort of work with them........VRX muffler sounds like a good compromise - fix the car up a little and then I'll start scouring wreckers to find one...

Buddy I'm maltese and yes I do know what it's like. In the end it's not going to cause them any harm, won't cause your car harm and won't cause you to wake up neighbours. it's so quiet they won't know you've changed it. Just go to a mates house and change it, it's 3 bolts and a gasket, very easy to change.
I got kicked out of my garage spot cause I was spending so much on the car, who cares, in the end it's your hobby, in my case my passion and I don't care what they throw at me

** what I mean to say is, your a grown man, no need to bow down to their EVERY command like a 6yo, its a muffler FFS your not having a bunch of groupies live in the garage, i'm sure theres bigger problems for them to deal with in life then their son putting on a VRX muffler

;1331198']Buddy I'm maltese and yes I do know what it's like. In the end it's not going to cause them any harm, won't cause your car harm and won't cause you to wake up neighbours. it's so quiet they won't know you've changed it. Just go to a mates house and change it, it's 3 bolts and a gasket, very easy to change.
I got kicked out of my garage spot cause I was spending so much on the car, who cares, in the end it's your hobby, in my case my passion and I don't care what they throw at me

** what I mean to say is, your a grown man, no need to bow down to their EVERY command like a 6yo, its a muffler FFS your not having a bunch of groupies live in the garage, i'm sure theres bigger problems for them to deal with in life then their son putting on a VRX muffler

I see what you're saying - but I still care about them and what they think - my parents have been really good to me, esp. the last year, for me to give them a I don't care what you say attitude - my parents don't deserve that.........with a bit of 'discussion' I'm sure the vrx muffler should be alright with them - just gotta find one now...

Dude I bought a turbocharger and mum had no idea what it was until iItold her. I just said it was a giant air pump, which, wasn't a lie ;)

If you keep doing that you'll never get anything done as you'll always need permission first, if it's not going to hurt them and you know what your doing, and it's your car and your money, don't see why you need permission, sure if you were going to supercharge it they'd know but a muffler.....how often do your parents check your exhaust tip?

Well have fun with that anyway - Remember I never said to disrespect them, just take it on your own accord, no need to get signed off on everything you do, with your money, to your car.

LOL at this whole conversation, i was only 17 (now 18) and i have a 2000 TJ sports, i got a full 2.5 inch cat back fitted while dad was away knew i he wouldnt really accept it, so stuff it il do it behind is back, i got the bumper cut to house a tip as well as it was a custom job, took him months to even realise, when he finaly realised he drove it up the street and said to me why is ur car so loud! i just said i got an exhaust he asked how much i said 300 lol was really 420 haha

oh and i would suspect this 02 sensor is my issue as well as im gettign only 450, k's out of a full tank of 95 RON, with an average fuel of approximately 15l/100km :/

I would check your tyre pressures given you have got new ones as I have found that it makes a significant difference to fuel ecomony. I run 43psi.

As for exhaust, an easy option would be a Lukey AL4-5597 Ultra Flow Muffler. Just bolts on. It's not intrusive. I asked my neighbour across the street whether he could hear it when I left for work at 6am and he said nup. Seriously, my engine and the fans makes more noise than the muffler.

seems like pretty normal economy to me. im using 12-14L/100, VRX with 18" rims. rims definitely make a difference. seems about the norm with most members

Well i dont have 18, buts 17s with 235 tires & my awesome 4 speed auto, i would never go over 12, 11.8 would be my worst

I would check your tyre pressures given you have got new ones as I have found that it makes a significant difference to fuel ecomony. I run 43psi.

As for exhaust, an easy option would be a Lukey AL4-5597 Ultra Flow Muffler. Just bolts on. It's not intrusive. I asked my neighbour across the street whether he could hear it when I left for work at 6am and he said nup. Seriously, my engine and the fans makes more noise than the muffler.

wow 43 psi is high, i run 35 for around town thats what bob jane recommended

wow 43 psi is high, i run 35 for around town thats what bob jane recommended

Dont worry about what Bob Jane recommended. Find out what works for you! I run 40psi in my 15's and 40psi in my 19's. There's no right or wrong, when it comes to tyre pressure, some may work better then others.

;1331276']Dont worry about what Bob Jane recommended. Find out what works for you! I run 40psi in my 15's and 40psi in my 19's. There's no right or wrong, when it comes to tyre pressure, some may work better then others.

cheers man, might give 40 a try im guessing its the same for the front and rear like 40 front 40 rear

cheers man, might give 40 a try im guessing its the same for the front and rear like 40 front 40 rear

Well I'm not telling you to put 40psi in lol, but you might find with more pressure, the car might handle better and you *might* see better economy, what they "recommend" is merely a compromise between the two to keep there ass's safe

yea alright, il give 38 a try first see if a notice a difference... i use to run 34 lol