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How Does Burst Silencer/exhaust Affect Fuel Consumption? - Car Talk - Nairaland

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How Does Burst Silencer/exhaust Affect Fuel Consumption? by abes(m): 1:49pm On Jul 20, 2009
This is a question i'm yet to get a technical answer on. What i keep hearing is because it makes more sound/noise, therefore it consumes more fuel.
Please can anyone explain this for us to understand,
ATM, i'm not convinced that a burst exhaust affects fuel consumption.
Over to you guys
Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by jolaogun(m): 3:04pm On Jul 20, 2009
I really wouldn't want to stress you about the technology but look at it from the double silencer vehicles. i want to believe yu know that they consume more fuel than the single silencer vehicles. so in the same vein, if there's an additional opening {thru burst} additional fuel is emitted thru it thus increasing fuel consumption of the vehicle coupled with the fact that they make more noise. If you're not satisfied with this yu can call me on 08028552222 for technical explanations.
Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by abes(m): 6:24am On Jul 21, 2009
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Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by Immune1(m): 11:27pm On Jul 21, 2009
So long the silencer or muffler is well tested and confirmed not to induce too much back pressure,i dont see how it can affect fuel consumption.May be increase in fuel consumption you referring to is the increment that normally follows when cars perform better due to enhanced and more spontaneous breathing of engine.
Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by abes(m): 5:42pm On Jul 22, 2009
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Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by sulazzi: 6:19pm On Jul 22, 2009
Never had any experience with a diesel engine ! heard they do not use spark plugs ! is that true and if so why??
Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by Midas02(m): 2:28am On Jul 23, 2009
Abes,

This is one of those myths about cars that are unfounded.

Exhaust systems only have two functions:
1. To reduce and refine noise emitted
2. To reduce and refine harmful gas emission

When you have a bursted muffler or pipe, the worst that can happen is that your car will loose its ability to control one or both of those factors listed above (depends on where it is bursted). The engine is unaffected and therefore the rate of fuel consumption is not a factor and is consequently NOT affected.

As a matter of fact, under the right circumstance, a bursted exhaust system may bring about a decrease in back pressure which gives the engine a very slight increase in power output which may or may not translate to a very very slight improvement in fuel consumption! (although, it depends more on the driving habit).

Truth is, most people tend to floor the pedal with reckless abandon when the rumbling sound of a bursted exhaust rears its ugly head. (perhaps out of fustration or they simply love the loud menacing sound). Apparantly the rumbling sound is a catalyst that ensures more aggressive driving and the consequent reduction in gasoline economy. But generally speaking, broken exhaust systems simply DO NOT affect fuel economy!

Jolaogun,

The type of exhaust system a car is fitted with is a reflection of the objectives of the engineers. Like I explained earlier, exhaust systems create back pressure which robs the engine of a few horses (horsepower). If and when it is the objective of the engineering department to maximize engine output, then a less restrictive exhaust system which allows faster gas flow is specified and fitted. A less restrictive exhaust system always ensures an increase in engine output. When you see a vehicle with dual or quad(4) exhaust tips, it is most often the telling sign of a more powerful engine.

A 4 cylinder engine that is tuned to maximize power output will most definitely consume more fuel than another 4 cylinder that has been designed to maximize fuel economy. For example, a Toyota Corolla's engine is tuned for economy rather than maximum power and thus the exhaust system is consequently designed to handle the limited power. However, a Toyota Celica GT or a Honda Prelude SI, although both fitted with 4 Cylinder engines, are sport cars and thus have been designed to maximize their engine output by using free flowing dual exhaust systems along with a host of other high performance features and components.

Having said this, it is also important to remember that most cars that spot dual exhaust systems are 6 cylinders or even 8 cylinders! Most 6 cylinder engines are fitted with an exhaust manifold that channels the exhaust from each set of 3 cylinders into a single pipe (on different sides of the block if the engine is configured as a V6). You really can't expect any 6 cylinder to match the fuel economy of a 4 cylinder engine. In recent years, powerful V8 engines have been fitted with quad exhaust systems to handle the power output which is often in excess of 300BHP!

In conclusion, you need to remember that the exhaust layout is more a function of design and intent rather than a parameter for economy. The fact that dual exhaust fitted car's usually consume more fuel is really a direct consequence of the more powerful and potent engines with which they may be fitted and NOT becos the exhaust system itself causes more consumption! The type of exhaust system a car is fitted with stems from the type of engine car is equipped with! I hope this clarifies it.

2 Likes

Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by Midas02(m): 4:23am On Jul 23, 2009
Sulazzi,

Diesel engines are quite different in design from petrol or gasoline engines. Unlike gasoline engines, diesel engines do not need or use spark plugs becos the fuel is ignited by the heat generated when air is compressed to a very high pressure. Gasoline engines use either 'Otto' cycle or 'Miller' cycle for the process of internal combustion. Gasoline internal combustion engines can either be a 4 stroke design or 2 stroke design. Essentially, most gasoline engines used in cars are designed with a 4 stroke process which means - Intake, Compression, Combustion and Exhaust strokes or stages.

Diesel engines however use a diesel cycle and can be designed either as a 2 stroke or a 4 stroke process. Most automobile diesel engines use the 4 stroke process. However, the difference between the gasoline 4 stroke and the diesel 4 stroke is in the Compression and Combustion strokes. In the Diesel engine the air intake is compressed to a very high pressure consequently generating heat. Vaporized diesel fuel is injected at this high pressure causing it to ignite (because of the heat that was generated). Diesel engines use injectors with very sensitive nozzles (becos of the need to vaporize) and this is why replacing the diesel fuel filter is an important maintenance procedure.

I hope this information has been useful.

1 Like

Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by oranges(m): 8:32am On Jul 23, 2009
@ Midas02, that is a job well done!!!. your contribution is very educative. I usually follow your contributions to topics to the last word. Pls keep up the good work.

1 Like

Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by abes(m): 4:47pm On Jul 23, 2009
@midas,
thanks so much for your contribution, i now have the facts i need to defend myself anytime this argument springs u again.
cheers wink
Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by abes(m): 8:21am On Sep 08, 2009
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Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by mdautotec(m): 12:07am On Sep 24, 2009
Hello! A busted / broken exhaust, we are assuming will be either of the following comoponents: exhaust manifold, intermediate 'A' pipe, catalytic converter. resonator, intermediate 'B' pipe, muffler, and any additional piping. These items generally rust due to age, water (road salt) etc. A hole or severe leakage (gasket), in any of these components will directly affect fuel economy.
The back pressure maintained at the engine is reduced; hence energy is sapped in pumping losses of, eg. a 4 stroke motor. The pumping loss is the negative / positive efficiency the engine is allowed to inhale air (intake), and exhale (exhaust) gasses, after the combustion process.
The faulty exhaust will create a negative backpressure on the exhaust side (ports) of the cylinder head, and the 4 stroke (cylinder) motor will automatically inhale (intake) more air to make up for the faster exit of the exhaust gasses.
Think of a four stroke (cylinder) engine as an air pump, intake ,and exhaust. Both sides have to maintained to create a steady (balanced) line pressure. Any restriction or leakage will upset the flow, and directly affect line (air) pressure.
The above is only a basic explanation on intake / exhaust. This is not what determines whether the engine is running lean (too much air), or rich (too much fuel).
All electronically controlled vehicles have an ELECTRONIC CONTROL MODULE / POWERTRIAN CONTROL MODULE, which work in conjunction with various sensors on the engine e.g. MAP (manifold absolute) pressure sensor, throttle body sensor, camshaft sensor etc.These sensors relay tiny voltages back and forth to the control modules to maintain proper ignition timing, efficient fuel curve etc.
The MAP (located on air intake) & oxygen sensor located in the exhaust manifold will determine the oxygen contect in the exhaust.
The negative back pressure created by the faulty exhaust will give a lean (too much air) reading back to the ELECTRONIC CONTROL MODULE. The ECM will then try and correct this by adding more fuel into the combustion chamber, by increasing fuel injectors duty cycle, in order to create maximum fuel efficiency.
Unfortunately, due to the busted / broken exhaust the high negative pumping loss is too excessive for the oxygen sensor (it cannot adjust), to give balanced readings to the ECM, the air is too much: hence the reading back to the ECU will be lean (too much air).
Since the ECM has no accurate reading it will increase the injector duty cycle, and dump more fuel into the engine, to keep it running, until the problem is fixed (THE LEAKING EXHAUST)!!!
THERE YOU HAVE IT, THIS IS HOW A FAULTY EXHAUST SYSTEM WILL AFFECT FUEL ECONOMY.
There are many other factors on racing / performance automobiles, and their less restrcitive exhaust systems, that despite being less restrictive, will actually slightly improve fuel economy, but that is another topic!!
Also, please note, that more exhaust oulets on a vehicle does not determine the most powerful naturally aspirated motors. This is a misconception, and is solely based on exhaust design, and structure.

Hope this was helpful!

Best regards

4 Likes

Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by abes(m): 6:54pm On Mar 11, 2012
bump
Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by ikeyman00(m): 9:49pm On Mar 11, 2012
@@@@

i think this might make more sense

there is ECU intergrated circuit; meaning there is a programme on a chip; meaning it has a critical air fuel mixture; which is the manufacturer factory settings.

so if it is rich/ high fuel and less air meaning more unburn carbon the catalyst tell the ECU then more fuel obviously burn

more air less fuel?

so i would assume that any blow on the exhaust line may have effect on the catalyst converter/oxygen sensor thereby the ECU will be feeding misreadings figure
Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by abes(m): 9:50pm On Jun 16, 2012
x
Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by Ninilowo(m): 8:58am On Jun 17, 2012
Midas02: Sulazzi,

Diesel engines are quite different in design from petrol or gasoline engines. Unlike gasoline engines, diesel engines do not need or use spark plugs becos the fuel is ignited by the heat generated when air is compressed to a very high pressure. Gasoline engines use either 'Otto' cycle or 'Miller' cycle for the process of internal combustion. Gasoline internal combustion engines can either be a 4 stroke design or 2 stroke design. Essentially, most gasoline engines used in cars are designed with a 4 stroke process which means - Intake, Compression, Combustion and Exhaust strokes or stages.

Diesel engines however use a diesel cycle and can be designed either as a 2 stroke or a 4 stroke process. Most automobile diesel engines use the 4 stroke process. However, the difference between the gasoline 4 stroke and the diesel 4 stroke is in the Compression and Combustion strokes. In the Diesel engine the air intake is compressed to a very high pressure consequently generating heat. Vaporized diesel fuel is injected at this high pressure causing it to ignite (because of the heat that was generated). Diesel engines use injectors with very sensitive nozzles (becos of the need to vaporize) and this is why replacing the diesel fuel filter is an important maintenance procedure.

I hope this information has been useful.
Good explanation from an automobile engineer. You brough back the memory of my school days.
Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by Somorin1(m): 4:44am On Feb 26, 2013
A few plausible attempts but here is the low down.

The simple answer is that the fuel consumption is affected because of lack of back pressure.

It has nothing to do with o2 sensors, etc The pre and post cat sensor doesn't know calculate exhaust flow after the last sensor.

On my non commute cars, the first thing I do is install a less restrictive cat back performance exhaust system, then a freeer flowing intake system and then program the ecu.

Basically the pistons will use less energy to push the exhaust gas out of the tailpipe.
Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by mdautotec(m): 10:29pm On Feb 26, 2013
Somorin#1:
A few plausible attempts but here is the low down.

The simple answer is that the fuel consumption is affected because of lack of back pressure.

It has nothing to do with o2 sensors, etc The pre and post cat sensor doesn't know calculate exhaust flow after the last sensor.

On my non commute cars, the first thing I do is install a less restrictive cat back performance exhaust system, then a freeer flowing intake system and then program the ecu.

Basically the pistons will use less energy to push the exhaust gas out of the tailpipe.


I wish to state Oxygen sensors and air/fuel sensors are a vital part of the system. These sensors measure the oxygen content in the exhaust and adjust the short and long term fuel trims in closed loop control.
Any alteration to a stock exhaust system will immediately affect your short term fuel trim. Lack of exhaust back pressure is not the only instance that will affect fuel consumption.
These sensors whether the system is running rich or lean relay oxygen content information via tiny voltage signal pulses to the engine control module.
If these sensors were not there then what information would the ECM use to control and maintain the fuel trim at 14.7:1 (perfect air fuel ratio - stoichiometric)?
In open loop control these sensors are not used, but only in closed loop; however that's another topic. These sensors are crucial for peak engine performance and yes, they will affect fuel economy if they go bad, as they will relay wrong information to the ECM.
Exhaust systems and design are a very vast topic.
Placing a free flow exhaust system and less restrictive intake system may yield slight performance gains in some vehicles, but putting the same set up in a different motor may actually hurt engine performance and fuel economy. You have to try different set ups based on engine design.
For example on a Honda motor a basic air intake, exhaust upgrade, performance plugs, headers etc will yield about 10 - 12 horsepower. In reality place your vehicle on a dynamometer and you will not see more than 7 - 9 hp due to friction and drivetrain losses.
You will likely not notice any deviation in fuel economy because the ECM can adjust injectors duty cycle up to 3 - 4% to compensate for the additional airflow in and out of the engine. Once again I highlight here there is more exhaust flow out of the engine which is measured by the oxygen sensor. The necessary adjustments (injector duty cycle) is carried out by the ECM, along with ignition timing curve etc.
For those who are interested it is difficult getting huge horsepower gains from a Honda motor just by adding aftermarket bolt on parts. Honda engines (intake runners, intake & exhaust head ports, manifold designs etc) are already designed and tuned to extract every ounce of power from small displacement engines.
Sorry to go off topic. It might interest some.
I used to drag race in Florida about 14 years ago running a Honda Prelude Si 96 model. Ported and polished cylinder head, performance intake, headers, cat back exhaust system, adjustable cam gears, high flow AEM fuel pump, fuel rail, fuel injectors and to top it off a 50 shot of Nos (Nitrous Oxide).
This is where I derive my knowledge from to a certain extent.
This is a great topic and it's good to learn from.

Good luck
Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by Somorin1(m): 9:56pm On Feb 27, 2013
md_autotec:


I wish to state Oxygen sensors and air/fuel sensors are a vital part of the system. These sensors measure the oxygen content in the exhaust and adjust the short and long term fuel trims in closed loop control.
Any alteration to a stock exhaust system will immediately affect your short term fuel trim. Lack of exhaust back pressure is not the only instance that will affect fuel consumption.
These sensors whether the system is running rich or lean relay oxygen content information via tiny voltage signal pulses to the engine control module.
If these sensors were not there then what information would the ECM use to control and maintain the fuel trim at 14.7:1 (perfect air fuel ratio - stoichiometric)?
In open loop control these sensors are not used, but only in closed loop; however that's another topic. These sensors are crucial for peak engine performance and yes, they will affect fuel economy if they go bad, as they will relay wrong information to the ECM.
Exhaust systems and design are a very vast topic.
Placing a free flow exhaust system and less restrictive intake system may yield slight performance gains in some vehicles, but putting the same set up in a different motor may actually hurt engine performance and fuel economy. You have to try different set ups based on engine design.
For example on a Honda motor a basic air intake, exhaust upgrade, performance plugs, headers etc will yield about 10 - 12 horsepower. In reality place your vehicle on a dynamometer and you will not see more than 7 - 9 hp due to friction and drivetrain losses.
You will likely not notice any deviation in fuel economy because the ECM can adjust injectors duty cycle up to 3 - 4% to compensate for the additional airflow in and out of the engine. Once again I highlight here there is more exhaust flow out of the engine which is measured by the oxygen sensor. The necessary adjustments (injector duty cycle) is carried out by the ECM, along with ignition timing curve etc.
For those who are interested it is difficult getting huge horsepower gains from a Honda motor just by adding aftermarket bolt on parts. Honda engines (intake runners, intake & exhaust head ports, manifold designs etc) are already designed and tuned to extract every ounce of power from small displacement engines.
Sorry to go off topic. It might interest some.
I used to drag race in Florida about 14 years ago running a Honda Prelude Si 96 model. Ported and polished cylinder head, performance intake, headers, cat back exhaust system, adjustable cam gears, high flow AEM fuel pump, fuel rail, fuel injectors and to top it off a 50 shot of Nos (Nitrous Oxide).
This is where I derive my knowledge from to a certain extent.
This is a great topic and it's good to learn from.

Good luck


The muffler does not have any sensor attached and is not part of the ECU process stream.

Any car/engine can benefit from performance upgraded if done with planning.

I have measured 7hp gain from just exhaust and intake alone. 7hp gain on a car that weighs 1100 pounds is heady.
Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by mdautotec(m): 11:02pm On Feb 27, 2013
Somorin#1:


The muffler does not have any sensor attached and is not part of the ECU process stream.

Any car/engine can benefit from performance upgraded if done with planning.

I have measured 7hp gain from just exhaust and intake alone. 7hp gain on a car that weighs 1100 pounds is heady.

The sensors are pre (air fuel sensor) and post (oxygen sensor) cat. converter and NOT attached to the muffler. These sensors are part of the Ecu process stream in conjunction with other sensors map, cam, crank etc to adjust ignition timing, fuel curve etc. Without the presence of these sensors the engine will never run at peak efficiency. It will surely run, just not efficiently.

Yes, any vehicle will benefit bolt on performance parts. How much one gains from a particular motor depends on the design of the motor itself and the type of systems (PARTS) used.

Once again you cannot generalize on what hp gains are
achieved. Each engine's characteristics are different.

Weight and friction losses rob horse power.

As a matter of fact it was actually closer to 8hp gain at the wheels on my 96 Prelude using an Aem cold air intake, dc sports stainless steel (light weight) headers, NOLOGY performance plugs and wires (with external ground straps) and a Greddy cat back exhaust system with 3.5 inch mandarel bent piping and a 5 inch outlet on the stainless steel muffler.

Hope this explains a bit better.

Regards
Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by Somorin1(m): 5:58am On Feb 28, 2013
md_autotec:

The sensors are pre (air fuel sensor) and post (oxygen sensor) cat. converter and NOT attached to the muffler. These sensors are part of the Ecu process stream in conjunction with other sensors map, cam, crank etc to adjust ignition timing, fuel curve etc. Without the presence of these sensors the engine will never run at peak efficiency. It will surely run, just not efficiently.

Yes, any vehicle will benefit bolt on performance parts. How much one gains from a particular motor depends on the design of the motor itself and the type of systems (PARTS) used.

Once again you cannot generalize on what hp gains are
achieved. Each engine's characteristics are different.

Weight and friction losses rob horse power.

As a matter of fact it was actually closer to 8hp gain at the wheels on my 96 Prelude using an Aem cold air intake, dc sports stainless steel (light weight) headers, NOLOGY performance plugs and wires (with external ground straps) and a Greddy cat back exhaust system with 3.5 inch mandarel bent piping and a 5 inch outlet on the stainless steel muffler.

Hope this explains a bit better.

Regards

You just repeated what I said.

Removing the muffler does not have any effect on fuel combustion as controlled by the ECU.

And you can absolutely generalize on horsepower gain from proven mods and I've never installed a bolt on that did not give me the advertised gain according to my GTech Pro. But I don;t buy the cheapest product out of China though. But that is not what I said on my post, I stated the exact horsepower gain I got from a specific mod on a specific car.
Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by mdautotec(m): 12:11pm On Feb 28, 2013
Somorin#1:


You just repeated what I said.

Removing the muffler does not have any effect on fuel combustion as controlled by the ECU.

And you can absolutely generalize on horsepower gain from proven mods and I've never installed a bolt on that did not give me the advertised gain according to my GTech Pro. But I don;t buy the cheapest product out of China though. But that is not what I said on my post, I stated the exact horsepower gain I got from a specific mod on a specific car.
Somorin#1:


You just repeated what I said.

Removing the muffler does not have any effect on fuel combustion as controlled by the ECU.

And you can absolutely generalize on horsepower gain from proven mods and I've never installed a bolt on that did not give me the advertised gain according to my GTech Pro. But I don;t buy the cheapest product out of China though. But that is not what I said on my post, I stated the exact horsepower gain I got from a specific mod on a specific car.

Firstly, did you mention you were using a GTech pro for HP calculation? If you use speed and power measuring devices then you can generalize on absolutely anything. GTech pro is a decent accelerometer, but a little optimistic on hp readings; good for generalization though. I say this because of the pitching of a vehicle under braking / acceleration. The difference in Hp readings (marginal error) are factors of suspension travel, chassis stiffness etc. That's again another topic. If you want real time readings then a vehicle dynamometer is the way to go. Although, yes, Gtech pro is fair, but you will never get an exact specific HP gain form a mod, as explained above. Again this is generalization. If you do not believe in this just try both variations and you will be pleasantly surprised. Although I do believe that G-Tech Pro has some new designs out that are pretty good, although I have not yet tested or received feedback.

I can understand what you are getting at by saying (Removing the muffler does not have any effect on fuel combustion as controlled by the ECU.), but it not accurate to be sincere. There is a reason why your or any vehicle is actually gaining or hurting in performance by removing an exhaust muffler or installing a free flow type. This is the wonder of the OBD II system.

If you remove the muffler you reduce engine back pressure and the exhaust gases expel a lot faster out of the exhaust side of the cylinder head. A lot of car enthusiasts do this to bump the hp rating from their motors. Although NOT ADVISABLE on a daily driven street vehicle. Anything you touch or tamper with on an intake or exhaust system will affect the fuel trim; hence indirectly affect what is available to the engine to ignite / burn (air fuel ratio and combustion). This will determine whether the engine will run rich or lean. This may also be confirmed from the byproducts of combustion (HC, Nox, CO2, CO etc)
Altering the fuel trim is actually done by the ECM from various inputs received from appropriate sensors (A/F, oxygen etc).

Removing an exhaust muffler on some vehicle will hurt the fuel economy more than others. All engines require a certain amount of back pressure to maintain good torque and horsepower. A good exhaust system (cat back) or muffler tuned for a specific motor will reduce back pressure just the right amount to give you good performance gains and at the same time a slight bump in fuel economy. On the other hand the motor will suffer if no or very little back pressure is applied.

Once again this all depends on engine and exhaust system designs.

As you mentioned, the best way is to go for the original tried and tested products from reputable Companies. You will be rest assured the products have been tested for your application!

Once again PLEASE NOTE this is a very vast topic. I am just highlighting a few areas from my personal experience, What works and may have worked for me is not necessary will work for others, vice versa.

All inputs are experiences are valid.

Regards
Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by Somorin1(m): 6:52pm On Feb 28, 2013
md_autotec:

Firstly, did you mention you were using a GTech pro for HP calculation? If you use speed and power measuring devices then you can generalize on absolutely anything. GTech pro is a decent accelerometer, but a little optimistic on hp readings; good for generalization though. I say this because of the pitching of a vehicle under braking / acceleration. The difference in Hp readings (marginal error) are factors of suspension travel, chassis stiffness etc. That's again another topic. If you want real time readings then a vehicle dynamometer is the way to go. Although, yes, Gtech pro is fair, but you will never get an exact specific HP gain form a mod, as explained above. Again this is generalization. If you do not believe in this just try both variations and you will be pleasantly surprised. Although I do believe that G-Tech Pro has some new designs out that are pretty good, although I have not yet tested or received feedback.

I can understand what you are getting at by saying (Removing the muffler does not have any effect on fuel combustion as controlled by the ECU.), but it not accurate to be sincere. There is a reason why your or any vehicle is actually gaining or hurting in performance by removing an exhaust muffler or installing a free flow type. This is the wonder of the OBD II system.

If you remove the muffler you reduce engine back pressure and the exhaust gases expel a lot faster out of the exhaust side of the cylinder head. A lot of car enthusiasts do this to bump the hp rating from their motors. Although NOT ADVISABLE on a daily driven street vehicle. Anything you touch or tamper with on an intake or exhaust system will affect the fuel trim; hence indirectly affect what is available to the engine to ignite / burn (air fuel ratio and combustion). This will determine whether the engine will run rich or lean. This may also be confirmed from the byproducts of combustion (HC, Nox, CO2, CO etc)
Altering the fuel trim is actually done by the ECM from various inputs received from appropriate sensors (A/F, oxygen etc).

Removing an exhaust muffler on some vehicle will hurt the fuel economy more than others. All engines require a certain amount of back pressure to maintain good torque and horsepower. A good exhaust system (cat back) or muffler tuned for a specific motor will reduce back pressure just the right amount to give you good performance gains and at the same time a slight bump in fuel economy. On the other hand the motor will suffer if no or very little back pressure is applied.

Once again this all depends on engine and exhaust system designs.

As you mentioned, the best way is to go for the original tried and tested products from reputable Companies. You will be rest assured the products have been tested for your application!

Once again PLEASE NOTE this is a very vast topic. I am just highlighting a few areas from my personal experience, What works and may have worked for me is not necessary will work for others, vice versa.

All inputs are experiences are valid.

Regards

I didn’t have to mention that I use GTech Pro, my assumption is that any self-respecting Autoist would have some sort of measuring devices in its arsenal. Regardless of that, GTech Pro does not monitor mpg per se. I don’t understand though why you would casually disregard this device when you haven’t spent time on it. When tuning my cars, either the software parameters or after installing bolt ons or other upgrades even as simple as changing my tires, I use my GTech Pro to aid me. When everything is buttoned down I then go to my local commercial accelerometer for final measurement (I usually wait for club days when one of the automotive clubs I belong to does a dyno day). My figures have never been off more than 0.1 %, so GTech Pro gets me close enough. As a Technical person professionally and an Autoist as a hobby I salute companies that develop and market instantly useful devices like accelerometers. The caveat is that it does require calibration and to be used properly by following the instruction. I have a dedicated section of NON PUBLIC road where I do my testing, my GTech is well installed with zero movements on the device itself and thus I get almost dead on measurements. If you approach any technical device as a flight of fancy then I am afraid that the result will show.

When you remove your muffler (only muffler, nothing to do with suspension, etc) the ECU does not see that since there are no sensors to monitor muffler removal. If back pressure is affected, which is not a total guarantee as some cars do come from the factory with very excellent flowing mufflers (example Mitsubishi Evolution, Corvette Z06), then the ECU accommodates with a different trim. I will wager and say that most modern turbo cars have excellent mufflers and any gain can usually be seen when the downpipe is replaced versus just a catback.

So to answer the OPs direct question, removing your muffler does not affect your fuel performance, mostly. Now if you enjoy hearing the noise of the exhaust and keep revving the engine or take advantage of the new found increase in power by doing jack rabbit starts, enjoying the previously unreachable power bands of the tachometer then fuel mileage will surfer.

I yield this very interesting thread and we’ll meet on another one I’m sure.
Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by mdautotec(m): 8:17pm On Feb 28, 2013
Somorin#1:


I didn’t have to mention that I use GTech Pro, my assumption is that any self-respecting Autoist would have some sort of measuring devices in its arsenal. Regardless of that, GTech Pro does not monitor mpg per se. I don’t understand though why you would casually disregard this device when you haven’t spent time on it. When tuning my cars, either the software parameters or after installing bolt ons or other upgrades even as simple as changing my tires, I use my GTech Pro to aid me. When everything is buttoned down I then go to my local commercial accelerometer for final measurement (I usually wait for club days when one of the automotive clubs I belong to does a dyno day). My figures have never been off more than 0.1 %, so GTech Pro gets me close enough. As a Technical person professionally and an Autoist as a hobby I salute companies that develop and market instantly useful devices like accelerometers. The caveat is that it does require calibration and to be used properly by following the instruction. I have a dedicated section of NON PUBLIC road where I do my testing, my GTech is well installed with zero movements on the device itself and thus I get almost dead on measurements. If you approach any technical device as a flight of fancy then I am afraid that the result will show.

When you remove your muffler (only muffler, nothing to do with suspension, etc) the ECU does not see that since there are no sensors to monitor muffler removal. If back pressure is affected, which is not a total guarantee as some cars do come from the factory with very excellent flowing mufflers (example Mitsubishi Evolution, Corvette Z06), then the ECU accommodates with a different trim. I will wager and say that most modern turbo cars have excellent mufflers and any gain can usually be seen when the downpipe is replaced versus just a catback.

So to answer the OPs direct question, removing your muffler does not affect your fuel performance, mostly. Now if you enjoy hearing the noise of the exhaust and keep revving the engine or take advantage of the new found increase in power by doing jack rabbit starts, enjoying the previously unreachable power bands of the tachometer then fuel mileage will surfer.

I yield this very interesting thread and we’ll meet on another one I’m sure.

Certainly I would like to keep posting on this great thread. Out of respect I do not dis-regard anything or what anyone says. I have my personal experiences as a Toyota and Honda tech for the last 19 years with ASE certifications. I do not know everything, neither does everyone else. We keep learning everyday.
I do not necessarily agree with some of your comments; however I do appreciate the input.
Wishing you the very best and yes hopefully we'll meet on another thread in the near future.

Regards
Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by 9icetoo(m): 12:12pm On Mar 01, 2013
i am not qualified yet to contribute to this thread. though i am very glad to learn a few tips here. Nice one, keep it coming peeps.
Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by mdautotec(m): 10:24pm On Mar 01, 2013
9icetoo: i am not qualified yet to contribute to this thread. though i am very glad to learn a few tips here. Nice one, keep it coming peeps.

You do not need to be qualified to contribute to this thread or any thread for that matter. Comments and questions are an integral part of the learning procedure.

Regards
Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by Trac: 6:29am On Mar 18, 2013
@Somorin

There are two principles in fluid mechanics and fluid dynamics. The Giovanni Venturi effect and Bernoulli's principle. Running unrestricted tubes would reduce velocity according to Bernoulli's principle. One could run free tubes in a forced induction setup because variables have been altered to still subscribe to the physics laws of Bernoulli's principle that pressure decrease in fluid as velocity of the fluid increases. This is the comprehensive summary of what MD' is talking about.

The back pressure and resonance MD_Autotec is stating is principled according to the Giovanni Venturi effect.
Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by Readonee35L(m): 10:21pm On Oct 23
An Educative thread
learned somethings
Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by baaliyah(m): 11:55pm On Oct 23
My car is sluggish and consumes more fuel when I have burst or leaking exhaust. I am no tech person, but I feel some pressure is lost when I drive with leaked pipe.
Re: How Does Burst Silencer/exhaust Affect Fuel Consumption? by lonelydora(m): 12:37am On Oct 24
mdautotec:
Hello! A busted / broken exhaust, we are assuming will be either of the following comoponents: exhaust manifold, intermediate 'A' pipe, catalytic converter. resonator, intermediate 'B' pipe, muffler, and any additional piping. These items generally rust due to age, water (road salt) etc. A hole or severe leakage (gasket), in any of these components will directly affect fuel economy.
The back pressure maintained at the engine is reduced; hence energy is sapped in pumping losses of, eg. a 4 stroke motor. The pumping loss is the negative / positive efficiency the engine is allowed to inhale air (intake), and exhale (exhaust) gasses, after the combustion process.
The faulty exhaust will create a negative backpressure on the exhaust side (ports) of the cylinder head, and the 4 stroke (cylinder) motor will automatically inhale (intake) more air to make up for the faster exit of the exhaust gasses.
Think of a four stroke (cylinder) engine as an air pump, intake ,and exhaust. Both sides have to maintained to create a steady (balanced) line pressure. Any restriction or leakage will upset the flow, and directly affect line (air) pressure.
The above is only a basic explanation on intake / exhaust. This is not what determines whether the engine is running lean (too much air), or rich (too much fuel).
All electronically controlled vehicles have an ELECTRONIC CONTROL MODULE / POWERTRIAN CONTROL MODULE, which work in conjunction with various sensors on the engine e.g. MAP (manifold absolute) pressure sensor, throttle body sensor, camshaft sensor etc.These sensors relay tiny voltages back and forth to the control modules to maintain proper ignition timing, efficient fuel curve etc.
The MAP (located on air intake) & oxygen sensor located in the exhaust manifold will determine the oxygen contect in the exhaust.
The negative back pressure created by the faulty exhaust will give a lean (too much air) reading back to the ELECTRONIC CONTROL MODULE. The ECM will then try and correct this by adding more fuel into the combustion chamber, by increasing fuel injectors duty cycle, in order to create maximum fuel efficiency.
Unfortunately, due to the busted / broken exhaust the high negative pumping loss is too excessive for the oxygen sensor (it cannot adjust), to give balanced readings to the ECM, the air is too much: hence the reading back to the ECU will be lean (too much air).
Since the ECM has no accurate reading it will increase the injector duty cycle, and dump more fuel into the engine, to keep it running, until the problem is fixed (THE LEAKING EXHAUST)!!!
THERE YOU HAVE IT, THIS IS HOW A FAULTY EXHAUST SYSTEM WILL AFFECT FUEL ECONOMY.
There are many other factors on racing / performance automobiles, and their less restrcitive exhaust systems, that despite being less restrictive, will actually slightly improve fuel economy, but that is another topic!!
Also, please note, that more exhaust oulets on a vehicle does not determine the most powerful naturally aspirated motors. This is a misconception, and is solely based on exhaust design, and structure.

Hope this was helpful!

Best regards

Best answer so far. No need to add mine again. You took it out of my mouth. Well done.

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