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Prokart2000

Exhaust uses more fuel?

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Posted · Original PosterOP

Hey everyone 

 

I'm not sure if anyone will know but recently I installed an exhaust to my fiesta (I'm not a boy racer I just like a good sounding car lol) which is basically the same as the oem straight pipe but the muffler is alot smaller. I think the newer exhaust is a slightly bigger diameter but not by much 

 

Would my mpg be effected at all? I haven't driven much but my average mpg is down a couple and the gauge seems to be going down quicker to me. This could be entirely placebo or me driving with higher revs more often but I was wondering if it could actually be an issue and if so how would I solve it? 

 

Many thanks again guys

 

Pro


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Well, lambda sensor (usually somewhere around engine exhaust manifold) may get different readings with exhaust different than what manufacturer specified, resulting in different mixture being produced in cylinders, resulting in different fuel consumption.

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Posted · Original PosterOP
1 minute ago, RejZoR said:

Well, lambda sensor (usually somewhere around engine exhaust manifold) may get different readings with exhaust different than what manufacturer specified, resulting in different mixture being produced in cylinders, resulting in different fuel consumption.

That's a good point actually, I didn't think it would effect it that much though. I guess there's not really an easy way to tell that or fix it


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if you got a ODB2 reader (something like ELM327) monitor your cars LTFT (long term fuel trim), it should fix itself over time. I ran my car with just exhaust manifold with cat and I was getting -%15 fuel trim.

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Posted · Original PosterOP
3 minutes ago, Levent said:

if you got a ODB2 reader (something like ELM327) monitor your cars LTFT (long term fuel trim), it should fix itself over time. I ran my car with just exhaust manifold with cat and I was getting -%15 fuel trim.

I have a Bluetooth one somewhere which I could try. 

 

How long would you say it takes to fix it, just so I know when it should be okay. 


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14 minutes ago, Prokart2000 said:

I have a Bluetooth one somewhere which I could try. 

 

How long would you say it takes to fix it, just so I know when it should be okay. 

No clue, my car was so damn obnoxious that I only drove around for 10 minutes and put rest of the exhaust back on. 

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Posted · Original PosterOP
2 minutes ago, Levent said:

No clue, my car was so damn obnoxious that I only drove around for 10 minutes and put rest of the exhaust back on. 

Ah okay no worries, I've done about 25 miles but it may take a while for it to adjust. 

 

Anything else I should measure or check? 


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32 minutes ago, RejZoR said:

Well, lambda sensor (usually somewhere around engine exhaust manifold) may get different readings with exhaust different than what manufacturer specified, resulting in different mixture being produced in cylinders, resulting in different fuel consumption.

Exhaust changes past the sensors wont make a difference to the readings


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Posted · Original PosterOP
7 minutes ago, iDeFecZx said:

Exhaust changes past the sensors wont make a difference to the readings

Hmm I guess that won't be it then, it's all past the cat. 


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25 miles is like 1/4 of 1/4 of the fuel gauge, you can't gauge your gas mileage off 1 gallon of driving. See what you're averaging after 4 full tanks.

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Posted · Original PosterOP
2 minutes ago, Bitter said:

25 miles is like 1/4 of 1/4 of the fuel gauge, you can't gauge your gas mileage off 1 gallon of driving. See what you're averaging after 4 full tanks.

Yeah that was the plan, I was gonna see how the mpg was differing after a while. 

 

I just noticed so wondered if the exhaust could make a difference 


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Posted · Original PosterOP
11 minutes ago, Bitter said:

Could be you like hearing it more so you're stepping on it a little harder.

Yeah that was my thoughts too, I'll see how it goes for a while and see what I think 


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27 minutes ago, Bitter said:

Could be you like hearing it more so you're stepping on it a little harder.

Part of it will be this and also the exhaust is now less restrictive allowing the engine to breathe better and *very slightly* adjust fuel trims for better performance as a result.

 


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Posted · Original PosterOP
7 minutes ago, iDeFecZx said:

Part of it will be this and also the exhaust is now less restrictive allowing the engine to breathe better and *very slightly* adjust fuel trims for better performance as a result.

 

I will try to drive it normally then lol

 

Will the fuel trims adjust or will that be how it is now consumption wise? 


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2 hours ago, iDeFecZx said:

Exhaust changes past the sensors wont make a difference to the readings

He said the new exhaust pipe is narrower. Gases can push back into the engine in such scenarios.

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23 minutes ago, RejZoR said:

He said the new exhaust pipe is narrower. Gases can push back into the engine in such scenarios.

No he said the muffler is smaller and the piping is slightly larger


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Posted · Original PosterOP
1 minute ago, iDeFecZx said:

No he said the muffler is smaller and the piping is slightly larger

Yeah the centre pipe as they called it is slightly larger in diameter but the actual muffling bit of the muffler is alot smaller which makes the sound. 

 

I will see how it adjusts, would there be any way to return it to the original mpg if it has dropped or do I have to live with it lol


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If you've changed the back pressure you'll have changed how well the cylinders fill. The intake and exhaust system is engineered around the engine and desired power delivery.

 

There is overlap between the intel and exhaust valves so that the flow of gasses out of the engine pulls more mixture in. In theory the exhaust valve closes just as the last of the exhaust gasses leave the cylinder, with minimal fresh charge loss. If the exhaust is more free flowing it dumps some of that mixture out of the exhaust reducing power and using more fuel. It also effects the air velocity through the intake tract and changes how much air gets drawn in in relation to the amount of fuel that's been metered.

 

It's safe to say that a combination of the noise (leading to more throttle) and exhaust changes will increase fuel consumption.

 

Being a Fiesta though you've pretty much doubled the value of the car ;)


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12 minutes ago, Prokart2000 said:

Yeah the centre pipe as they called it is slightly larger in diameter but the actual muffling bit of the muffler is alot smaller which makes the sound. 

 

I will see how it adjusts, would there be any way to return it to the original mpg if it has dropped or do I have to live with it lol

You are stressing about an inconsequential amount of miles per gallon. You'd get a larger difference of miles per gallon by properly inflating your tires and making sure you don't have excess weight in your car (trash, clothes, change, etc.). Everything being said at this point is only theory and based on one, obtuse data point you have provided. Run the car for 4 or 5 tanks, let the computer adjust, and if you still feel like there is an issue, then diagnostics can be started.

 

12 minutes ago, Prokart2000 said:

would there be any way to return it to the original mpg if it has dropped or do I have to live with it

If you have the same air filter for over a year, you'd see a change in mileage. If you turn on the A/C, you'd see a change in mileage. If you install non-standard tire sizes, run them bald, or low-pressure, you'd see a change in mileage. If you hit all red lights, versus all green lights, you'd see a change in mileage. All of these, in various degrees, will have a larger impact on your fuel mileage than the exhaust you just changed, especially if it is after the catalytic converter.


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Posted · Original PosterOP
6 minutes ago, Curious Pineapple said:

If you've changed the back pressure you'll have changed how well the cylinders fill. The intake and exhaust system is engineered around the engine and desired power delivery.

 

There is overlap between the intel and exhaust valves so that the flow of gasses out of the engine pulls more mixture in. In theory the exhaust valve closes just as the last of the exhaust gasses leave the cylinder, with minimal fresh charge loss. If the exhaust is more free flowing it dumps some of that mixture out of the exhaust reducing power and using more fuel. It also effects the air velocity through the intake tract and changes how much air gets drawn in in relation to the amount of fuel that's been metered.

 

It's safe to say that a combination of the noise (leading to more throttle) and exhaust changes will increase fuel consumption.

 

Being a Fiesta though you've pretty much doubled the value of the car ;)

Ah okay thank you for the detailed explanation, I guess there's no way I can fix that then😂

 

It's a well looked after car really so maybe tripled the value😉

 

5 minutes ago, The1Dickens said:

You are stressing about an inconsequential amount of miles per gallon. You'd get a larger difference of miles per gallon by properly inflating your tires and making sure you don't have excess weight in your car (trash, clothes, change, etc.). Everything being said at this point is only theory and based on one, obtuse data point you have provided. Run the car for 4 or 5 tanks, let the computer adjust, and if you still feel like there is an issue, then diagnostics can be started.

 

If you have the same air filter for over a year, you'd see a change in mileage. If you turn on the A/C, you'd see a change in mileage. If you install non-standard tire sizes, run them bald, or low-pressure, you'd see a change in mileage. If you hit all red lights, versus all green lights, you'd see a change in mileage. All of these, in various degrees, will have a larger impact on your fuel mileage than the exhaust you just changed, especially if it is after the catalytic converter.

Thank you for the reply, I will give it a few tanks and see how it goes and adjusts, it has been with the stock exhaust for years so its probably confused! For the record I do try to keep my pressures in check😂


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if you only changing the muffler part, aka make it louder, not very much. since the purpose of the muffler is absorbing kinetic energy, turning it into thermal energy (speed which the exaust gas leaving the system) by forcing it thru a maze.

 

however the diameter of the exhaust section (the part from exhaust maifold to catalytic converter) is crucial to the engine's performance, dont change it unless you know what you're doing.


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Posted · Original PosterOP
20 minutes ago, zassou said:

if you only changing the muffler part, aka make it louder, not very much. since the purpose of the muffler is absorbing kinetic energy, turning it into thermal energy (speed which the exaust gas leaving the system) by forcing it thru a maze.

 

however the diameter of the exhaust section (the part from exhaust maifold to catalytic converter) is crucial to the engine's performance, dont change it unless you know what you're doing.

The diameter of the pipe is slighter wider but this is after the cat only as my cat is fairly close to the exhaust manifold


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No for several reasons:

- Its fuel injection, so the computer is programmed to add a certain amount of fuel for the amount of oxygen in the engine or something IDK, but its not determined by the exhaust. 

- You aren't changing the whole exhaust, more importantly the headers, so the diameter for the flow coming out of the engine is the same anyway. 

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Posted · Original PosterOP
On 10/26/2019 at 11:52 PM, floofer said:

 

On 10/26/2019 at 11:24 PM, zassou said:

 

On 10/26/2019 at 9:53 PM, The1Dickens said:

 

Hi all again

 

Sorry for reigniting this post but it's been a while and I have some questions. 

 

My biggest issue that I'm finding at the moment is that I find it seems to be lacking some power on acceleration in comparison to what it used to have (I'm not sure if it's placebo but I don't think it is) and i didn't think an exhaust would cause a noticeable difference but I could be massively wrong. 

 

Also I have found the mpg is slightly down on what it used to get although it has got slightly better. It's much worse when the engine is could though. 

 

Would you recommend I purchase an oem backbox and just run that instead? 

 

Many thanks again 

 

Pro


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