is exhaust back pressure a myth?

[TitanRev]

I think everyone is sharing based on experience and trial and error....well here I want to share mine...this is based on observation and my theory....

From the exhaust port to the primary runner down until the bottom of the engine. This section the exhaust gas will be at the hottest since it's the closest to the exhaust port. That's why you see most headers on turbos or NA they start to glow hot 1st around this area....so as the exhaust gas travels further away from the engine it starts to cool down. The whole exhaust acts as a cooling conductor and in physics "heat will always conduct to the a cooler area"

So to improve scavenging, flow or velocity of the exhaust out of the port is very important because you want the exhaust to exit the chamber as much as possible before the valve closes and the intake stroke starts.

So we go back to the temperature 1st, hotter gas have higher pressure and higher flow in a confined space. So at the start of the primary runner you want the runner diameter to be bigger because the gas is super hot at that stage and it will need as much space it have to flow out of the chamber as much as possible...but after it gets under the engine it starts to cool down and in order to maintain the flow you reduce the piping diameter...this forces the hot exhaust that trying to cold down won't have a too steep temp drop...you force hot air into a smaller area it's velocity increase and it's temp drop will reduce....(just like heater use in winter, the pipe where the heat is given out is small instead of big) By doing this, you maintain the flow of the exhaust in a control area. But this does not mean you reduce the size to 1 inch is good because it will cause pressure to build up also....the reduction is size needs to be calculate and done in tandem with the intake.

That's why, when you use a bigger pipe at the rear, the exhaust gas have much more area to expand and cool down (cool air is heavier) and when you use a smaller exhaust the temp drop won't be too steep....a very good actual test is, you put your leg at a small medium size muffler, you can feel the exhaust gas pushing and blowing against your leg at a distance...compare that to a big muffler, the exhaust that exit is slow and sometimes you can feel it blowing on your leg.....

For those drag car that is posted by member here especially the 3rd picture, you can see that the exit diameter is smaller. Some what tapered...this maintain the exit velocity of the gas....

 

[DeaconFrost]

I think everyone is sharing based on experience and trial and error....well here I want to share mine...this is based on observation and my theory....

From the exhaust port to the primary runner down until the bottom of the engine. This section the exhaust gas will be at the hottest since it's the closest to the exhaust port. That's why you see most headers on turbos or NA they start to glow hot 1st around this area....so as the exhaust gas travels further away from the engine it starts to cool down. The whole exhaust acts as a cooling conductor and in physics "heat will always conduct to the a cooler area"

So to improve scavenging, flow or velocity of the exhaust out of the port is very important because you want the exhaust to exit the chamber as much as possible before the valve closes and the intake stroke starts.

So we go back to the temperature 1st, hotter gas have higher pressure and higher flow in a confined space. So at the start of the primary runner you want the runner diameter to be bigger because the gas is super hot at that stage and it will need as much space it have to flow out of the chamber as much as possible...but after it gets under the engine it starts to cool down and in order to maintain the flow you reduce the piping diameter...this forces the hot exhaust that trying to cold down won't have a too steep temp drop...you force hot air into a smaller area it's velocity increase and it's temp drop will reduce....(just like heater use in winter, the pipe where the heat is given out is small instead of big) By doing this, you maintain the flow of the exhaust in a control area. But this does not mean you reduce the size to 1 inch is good because it will cause pressure to build up also....the reduction is size needs to be calculate and done in tandem with the intake.

That's why, when you use a bigger pipe at the rear, the exhaust gas have much more area to expand and cool down (cool air is heavier) and when you use a smaller exhaust the temp drop won't be too steep....a very good actual test is, you put your leg at a small medium size muffler, you can feel the exhaust gas pushing and blowing against your leg at a distance...compare that to a big muffler, the exhaust that exit is slow and sometimes you can feel it blowing on your leg.....

For those drag car that is posted by member here especially the 3rd picture, you can see that the exit diameter is smaller. Some what tapered...this maintain the exit velocity of the gas....

Very interesting I can see the point here.

---------- Post added at 08:16 PM ---------- 6 hour anti-bump limit - Previous post was at 08:08 PM ----------

It's not the rule. If you look closely at an F1 car, they have this 2 huge exhaust pipe coming out of the body and terminated before the end of the car. Here's why I prefer no.2 if I am not a dragster. The exhaust air amount from an F1 car is not little. This hot air, blowing out from the exhaust like a jet actually helps in giving more downforce to the car as it hits the rear wing.

This is why the following rule was enforced:
Also shown here are the exhaust tailpipes (red arrow, centre left), which must extend at least 170 to 185mm behind the rear axle line (and have a single exit).

Formula 1® - The Official F1® Website

It can be seen that the difference between F1 cars and NHRA dragsters is the distance - lots of laps vs. one run down the straight. In F1 cars, outright performance need to make some compromise for practicality.

 

[TitanRev]

Just my input for race cars, the tail pipe is bigger at the tip example like F1 because their engines are what V8 or V10 so you have a lot of primary runners joining up together at each side and in a very narrow space...the bends from the exhaust ports is much more angled that our road car....in velocity term...bend creates pressure and hence the bigger exhaust tips at the end so that all the pressure can be let off as much as possible but this does not apply to our road going car with puny little 4 bangers....Also race cars have different gear ratios than our daily car which can be made to make use of the engine powerband....

 

[Waiora_ProTuner]

nice discussion here.

regarding the heater/radiator thing, where it have smaller piping..it actually have lots of small piping rather than 1 big pipe..purpose? more area for heat exchange...and the total area should be more than inlet so the fluid inside would be slower thus better heat exchange..its not a good comparison/example here btw...

the rules for road car is = exhaust must exit at the back.
and reduce noise..

regarding the temperature drop, yes...
cooler air are heavier, yes..
but why they didn't coat it with ceramic coating...or thermal wrap? why the complexity?
and even it drops so much, its still higher temperature than atmosphere...

Ferrari 458 have 3 exit..GTR have 4...no problem..
even though all comes through 1 pipe in the center...for scavenging..

regarding the 2rd dragster picture...i bet the bigger piping is only 'cover'..no welding there..
its all same diameter..see the braided tubing goes inside?

 

[TitanRev]

nice discussion here.

regarding the heater/radiator thing, where it have smaller piping..it actually have lots of small piping rather than 1 big pipe..purpose? more area for heat exchange...and the total area should be more than inlet so the fluid inside would be slower thus better heat exchange..its not a good comparison/example here btw...

the rules for road car is = exhaust must exit at the back.
and reduce noise..

regarding the temperature drop, yes...
cooler air are heavier, yes..
but why they didn't coat it with ceramic coating...or thermal wrap? why the complexity?
and even it drops so much, its still higher temperature than atmosphere...

Ferrari 458 have 3 exit..GTR have 4...no problem..
even though all comes through 1 pipe in the center...for scavenging..

regarding the 2rd dragster picture...i bet the bigger piping is only 'cover'..no welding there..
its all same diameter..see the braided tubing goes inside?

The heater for winter use have smaller diameter piping because they want to reduce the temp drop across the heater surface...because the heated steam comes from a boiler and is fed throughout the entire house. Imagine you use the same diameter as the delivery pipe at the heater the temp would have drop more already...that's why heater pipe is smaller than the delivery pipe. This increase the steam velocity and pressure which in turn heat up the steam.

Bro, engine capacity different between R35 and daily sub 2 liter engine with 4 bangers.....the exhaust temp at the muffler tip is not so much higher than atmo....try testing with a temp meter you will see....regarding coating....it's also an option but if we do not consider coating then you need to find another way. Actually tapered or stepped system Supersprint is using you can check it out....It's not something entirely new....

About the dragstar tubing, notice the burn marks at the braided line....it's not just a cover....

Also R35 exhaust is not totally single pipe from the downpipe all the way to the back....the joint into 1 pipie section is very short only then split into 2 again. Some have longer 1 pipe design like Meistercraft. Also you can notice the smaller diameter after the split pipe compare to the single diameter. The most important is still the primary runners out from the exhaust port section. For the Ferrari 458 is you notice the center exhaust pipe is smaller in diameter than the 2 at the sides. There's a valve system in the 458 exhaust. When idling and sub 3K RPM only the center exhaust is functioning. The outer 2 is only activated at RPM above 3K. The center exit is the joining from 2 muffler while the 2 at the side is directly from the 2 muffler...

 

[DeaconFrost]

Also R35 exhaust is not totally single pipe from the downpipe all the way to the back....the joint into 1 pipie section is very short only then split into 2 again. Some have longer 1 pipe design like Meistercraft. Also you can notice the smaller diameter after the split pipe compare to the single diameter. The most important is still the primary runners out from the exhaust port section. For the Ferrari 458 is you notice the center exhaust pipe is smaller in diameter than the 2 at the sides. There's a valve system in the 458 exhaust. When idling and sub 3K RPM only the center exhaust is functioning. The outer 2 is only activated at RPM above 3K. The center exit is the joining from 2 muffler while the 2 at the side is directly from the 2 muffler...

Very interesting info bro.

 

[TitanRev]

Very interesting info bro.

You can check those tuning house that offer exhaust to R35 and 458...Kakimoto especially their titanium exhaust for the R35 where the single piping split into 2 section it gets smaller...

While the 458, you can check TUBI or capristo....the stock system also came with the valve thingy just that some people bypass it so that it sounds louder at idle....if you can see the real thing in flesh try to notice the center exhaust....in actual the pipe is a merging of 2 D shape muffler at the end....while the 2 on the side is full pipe....

 

[ixeo]

You can check those tuning house that offer exhaust to R35 and 458...Kakimoto especially their titanium exhaust for the R35 where the single piping split into 2 section it gets smaller...

While the 458, you can check TUBI or capristo....the stock system also came with the valve thingy just that some people bypass it so that it sounds louder at idle....if you can see the real thing in flesh try to notice the center exhaust....in actual the pipe is a merging of 2 D shape muffler at the end....while the 2 on the side is full pipe....

They got titanium exhaust for R35 meh?

Oh wait, this one got R. cabutz.

 

[TitanRev]

They got titanium exhaust for R35 meh?

Oh wait, this one got R. cabutz.

Not this local kaki la...is the one from Japan....this one below...
Š`–{‰ü KAKIMOTORACINGbŽ©“®ŽÔƒ}ƒtƒ‰[“™‚̃p[ƒcƒ[ƒJ[

 

[hex999]

Whats the difference between a resonator and a straight bullet? Are they the same thing? Does a resonator reduce noticeable hp? Currently running with no midbox. Getting sick of the droaning sound when cruising. How do i get rid of that sound but still keep the exhaust sound raspy?

 

[TitanRev]

Whats the difference between a resonator and a straight bullet? Are they the same thing? Does a resonator reduce noticeable hp? Currently running with no midbox. Getting sick of the droaning sound when cruising. How do i get rid of that sound but still keep the exhaust sound raspy?

Actually I don't know why there's so many names.....

Whether it's a oval shape or straight through bullet (local call it) They are all resonator box aka mid box.....just the shape is different...resonator function is to reduce the sound decibel of the exhaust by cancelling off the sound with sound reflection from the wall.

Resonator can come in 2 types, most common is using glass fiber stuff inside it to absorb the sound while some have tubing inside that let the sound bounce back and forth inside it to dampen the exhaust note.....

In actual, a properly made exhaust will only consist of:
extractor>>>CAT>>>downpipe>>>midbox (some cars have 2)>>>rear piping>>>>rear muffler...

For me, I have find that using an oval shape midbox is the best to dampen sound level at the rear muffler because it packs more sound absorbing material than a straight through midbox.

 

[pwhyze]

Actually I don't know why there's so many names.....

Whether it's a oval shape or straight through bullet (local call it) They are all resonator box aka mid box.....just the shape is different...resonator function is to reduce the sound decibel of the exhaust by cancelling off the sound with sound reflection from the wall.

Resonator can come in 2 types, most common is using glass fiber stuff inside it to absorb the sound while some have tubing inside that let the sound bounce back and forth inside it to dampen the exhaust note.....

In actual, a properly made exhaust will only consist of:
extractor>>>CAT>>>downpipe>>>midbox (some cars have 2)>>>rear piping>>>>rear muffler...

For me, I have find that using an oval shape midbox is the best to dampen sound level at the rear muffler because it packs more sound absorbing material than a straight through midbox.

Good post. I always find terms like 'bullet', 'mid-box', 'resonator' , 'nenas' and such so confusing.

 

[TitanRev]

Good post. I always find terms like 'bullet', 'mid-box', 'resonator' , 'nenas' and such so confusing.

Nenas is different...it's a flexible joint after the extractor or downpipe. The use of the nenas or more proper term flexi joint is to reduce the stress on the exhaust piping from vibration as the flexi joint absorbs it from the rocking of the engine front and back or left to right when you throttle....because if you notice from underneath the car, you whole will shake when you lift off the throttle from a hard acceleration. Imagine a rigid piping without any flexible area...over time, you get crack exhaust mount, crack welding area..etc...

 

[Izso]

Hex99 : a resonator is exactly that. It resonates and reduces the sound. I hate the droning noise which is why I have a resonator and not a bullet. A resonator is a straight pipe that's perforated and has a large padded canister that's usually covered with fibreglass. Absorbs a lot of the noise before it reaches the muffler. I have the raspy noise minus the drone.

There's a few terms that need clearing up apparently. Let's start with the top :

Extractor / header - the thing that the engine breathes out to.

Pineapple / flexible joint / nenas - the thing that the extractor connects to which is connected to the adjoining hoses. This flexible joint is needed so the rest of the piping has some flexibility in terms of movement. Otherwise the machining has to be perfect to have one continuous pipe from the extractor onwards.

Resonator / mid muffler - this thing is exactly that. It resonates or muffles the exhaust. Usually used in the middle in place of the catcon.

Catcon @ catalytic convertor - this thing has trace amounts of platinum and other precious metals and it filters toxins from your exhaust. Most irresponsible people remove it because it's also one of the most restrictive portions of your exhaust. There are such things as high-flow catcons such as those from Magnaflow but they usually cost a lot money.

Bullet - most cheapest alternative to the resonator or mid-muffler. Kinda useless if you ask me unless you don't have much money to spend.

muffler / rear muffler - has two types generally speaking, baffled S-flow or straight flow.

 

[hex999]

Hex99 : a resonator is exactly that. It resonates and reduces the sound. I hate the droning noise which is why I have a resonator and not a bullet. A resonator is a straight pipe that's perforated and has a large padded canister that's usually covered with fibreglass. Absorbs a lot of the noise before it reaches the muffler. I have the raspy noise minus the drone.

There's a few terms that need clearing up apparently. Let's start with the top :

Extractor / header - the thing that the engine breathes out to.

Pineapple / flexible joint / nenas - the thing that the extractor connects to which is connected to the adjoining hoses. This flexible joint is needed so the rest of the piping has some flexibility in terms of movement. Otherwise the machining has to be perfect to have one continuous pipe from the extractor onwards.

Resonator / mid muffler - this thing is exactly that. It resonates or muffles the exhaust. Usually used in the middle in place of the catcon.

Catcon @ catalytic convertor - this thing has trace amounts of platinum and other precious metals and it filters toxins from your exhaust. Most irresponsible people remove it because it's also one of the most restrictive portions of your exhaust. There are such things as high-flow catcons such as those from Magnaflow but they usually cost a lot money.

Bullet - most cheapest alternative to the resonator or mid-muffler. Kinda useless if you ask me unless you don't have much money to spend.

muffler / rear muffler - has two types generally speaking, baffled S-flow or straight flow.

Awesome information. I saw some exhaust shop actually use a rear mufler as the mid mufler.. in the end owner complains on massive power loss..

Some exhaust shop boss even claims that a bullet and a resonator is the same thing. Makes it really confusing .. thanks alot of the clarification.

 

[TitanRev]

Actually bullet and resonator they are resonators just different in design...for "bullet" it has lesser sound absorbing material so it does not absorb much sound like an oval shape resonator...that's why you will see price difference between the 2.

 

[jeffayn]

wow.. really a great improvement from the 80s...hahaha....

some further correction here....

actually.. a resonator as it sound...it use resonance as tool to cancel out wave length..

so the mid box you guys talk about or the rear box can be a resonator too...

bullet in general is round tubing with pack or un pack, so if pack... it is relying absorption to absorb the sound wavelenght , if is not pack, is actually using resonance theory to lower down the noise, but a perforated pin hole bullet relying on resonance for noise reduction ... well... let just say it wont work right ... a scale hole , or louvred one will work much better...

exhaust, silencer, muffler and bla bla bla... well.. is just the term used in different country, you go to australia, no one know what is a bullet... but they know what is a hotdog... hahaha.... you go to uk , you say muffler they give u a ear muffler, the call them the silencer...... if you go us , you say you wan a silencer... die lor... you get the silence for your gun .... hahhaaa...

japanese vehicle manufacturer hate fiber.... because it cost alot.. and it doesn last long... so 95% of their vehicle , the exhaust system is purely resonance , sound cancelling design.

the europeans in the other hand.. really love their packed muffler.......and seriously.. they do sound much better compare to japanese oem muffler.. but harder to produce and cost alot..... now alot of the european exhaust comes in hybrid mood which combine cancelling and absorption, so that is why their car exhaust sound so little....

the mid muffler, why the oval shape will sound lesser than bullet, is because... they are prettier ? haha.. of course not... given the same size and material, the oval shape will sound lesser because as the sound wave travel it will go back and forward, the oval one give the wave to travel in different direction and back forward in different time.. not like the round one where only uni direction all bound back to center at more or less same time.....

if you pay little more attention... you will seee the european car model muffler is very very weird in shape , with bump here there... well.. these are not just for weird look to make you pay more .. but it custom design to fit in the car and also sound the right pitch.... if you fir an a6 muffler in a4, it will not sound the same.....

true... the american and european exhaust people make million dollar room just to tune the exhaust product to the right pitch, some even hire 3rd party engineering company to create signature sound for specific model of car and also bikes..... but as for the japanese... well.. i don see much coming from there.... maybe i will update myself more... the europeans had been doing this for decades, well before i in automotive line...

regard the catalytic converter ... well is alot of misconception.. the catalytic converter convert , convert harmful gas to less harmful gas so Malaysian, don cut the catalytic converter as soon as you get the car OK ? be more eco friendly please...... and they don filter... what filter in exhaust system is only DPF (Diesel particle Filter) and which is still not enforce in malaysia yet......

 

[Willi3]

hey bros...still new in this field of exhaust but apparently it seems like now there are people that put 2 mid box aka tabung...its said that it will increase power and lowers the FC.... applicant to auto car it seems...like my honda city 09...which by the way is still has virgin exhaust...so from what i read...for AT cars...the backflow have to be higher?....

 

[Izso]

hey bros...still new in this field of exhaust but apparently it seems like now there are people that put 2 mid box aka tabung...its said that it will increase power and lowers the FC.... applicant to auto car it seems...like my honda city 09...which by the way is still has virgin exhaust...so from what i read...for AT cars...the backflow have to be higher?....

First understand what exhaust is.

Exhaust is hot gases being pushed out from the combustion chamber to the atmosphere. By adding restrictions or whatever will not increase power or lower FC because power is generated in the engine, not the exhaust. Having said that however, how efficiently the exhaust is exhaled depends on the exhaust setup and the more efficiently it is exhaled, the better for the engine to 'breathe', therefore be more efficient. There's another thing called scavenging which is essential for an exhaust to work efficiently. Too much or too little and it won't help your engine (Race engines are the exception).

Autos require a little bit of back pressure to shift properly. Put a straight flow and the gear changes will be ridiculously high in the rev range. Too much back pressure and your car will struggle to move. Kinda like you trying to have a shit with a cork plugged up your ass which has a small hole for you to force the shit out from.

Exhausts is subjective (depending on your engine) and listening to every Tom Dick and Harry will not only make you a poor man, it'll also make your car suffer. Take time to do some research and then only make an educated decision.