something. There is no doubt that exhaust flow is important, but don't forget about scavenging. Exhaust flow is much different from flow in an intake manifold or cylinder head. If exhaust flow was continuous, then flow numbers may be the most important, but exhaust flow is not continuous, it is pulsating. Most muffler manufacturers don't make a scavenging muffler, so they advertise big flow numbers. I am not saying that you should not install a high flowing muffler, but if you want some extra performance, then get a scavenging muffler to help pull out exhaust gases from the combustion chambers. Flowmaster is one company that manufacturers scavenging type mufflers. There are reasons why people install various types of mufflers (looks, sound, price, etc.), but if it's performance you want, then look around.

Don

 

Is Borla a scavenging style muffler?

 

Yeah ok, Flowmaster makes scavenging mufflers, but other don't?

Wonder why there are other mufflers out there that will outflow flowmasters HP wise on a dyno.

And I thought scavengine was all over with after the headers anyways, that's where you need scavenging, not in the muffler, that's where tuning is important at the headers not the muffler.

 

Port flow isn't pulsating? Intake flow isn't pulsating? TB flow isn't pulsating? You better believe they are!

About the only difference is that exhaust gases are hot, changing the speed of sound (requiring longer tubes to tune to the same RPM). Exhaust is also "dry" - unlike a "wet" intake system like carb or TBI, but TPI is dry right up to the intake port in the head (minimizing the effect of changing the speed of sound with varying fuel/air mixture ratio).

If someone is claiming that their muffler is scavaging exhaust gases 10' away from the exhaust port, through numerous bends and a couple of collectors & y's, after 8 cylinders' worth of flow have been mixed together, after passing through an expansion chamber called a catalytic converter, then I'd say it's time to see some test data to back that up.

 

86FyrBrd
Is Borla a scavenging style muffler?

The only scavenging muffler that I know of is made by Flowmaster.


Mark A Shields
And I thought scavengine was all over with after the headers anyways, that's where you need scavenging, not in the muffler, that's where tuning is important at the headers not the muffler.

Put your hand near the opening of your tail pipe (the exhaust gas may be hot). Do you feel a smooth flow or a pulsating flow? Each exhaust pulse that comes down the exhaust pipe brings with it a low pressure area directly behind it. Each low pressure area in the pipe helps to pull (scavenge) the next pulse through the system. The Flowmaster muffler uses the sound and pulse energy contained in the exaust gas to create a low pressure area that is greater than the one created by the pulse alone. That increases the scavenging in the exhaust system.


five7kid
Port flow isn't pulsating? Intake flow isn't pulsating? TB flow isn't pulsating? You better believe they are!

Certainly they are. The engine is an air pump. My intension was directed at the way intake manifolds and cylinder heads and mufflers are tested by the manufacturers. In the shop they use flow benches and as for as the intake hardware is concerned, the flow numbers indicate prettly accurately how the parts will function. But not so for the mufflers.

Don
P.S. I am not affiliated with Flowmaster, but I do believe in their technology.

 

OK everybody.

During the exhaust stroke, a good way for an engine to lose power is through back pressure. The exhaust valve(s) open at the beginning of the exhaust stroke, and then the piston pushes the exhaust gases out of the cylinder. If there is any amount of resistance that the piston has to push against to force the exhaust gases out, power is wasted. Using two exhaust valves rather than one improves the flow by making the hole that the exhaust gases travel through larger.

Backpressure is exactly what it sounds like. It is a high pressure area or system in the exhaust that blocks other gases from getting by. This is in a way related to velocity because the velocity is slowed because of the Backpressure. Velocity is where the power comes from.

What you have to understand is that exhaust leaves the cylinders with a high pressure "front" and and almost vacuum for a "tale". This is what "pulls" the exhaust through the pipes. The vacuum created pulls the pulses through. When one high pressure pulse meets backpressure, another high pressure area, you get a collision that is detrimental to performance. If you think about it, you'll realize that since stock exhausts are so good at restricting that they'll actually ram the exhaust pulses together and actually make pretty darn good low-end torque! But this sacrifices horsepower which is not good nor is it efficient.

What does all this mean?? Well basically backpressure is BAD!

also, exhaust gas is hot. And we'd like to keep it hot throughout the exhaust system. Why? The answer is simple. Cold air is dense air, and dense air is heavy air. You don't want an engine to be pushing a heavy mass of exhaust gas out of the tailpipe. An extremely large exhaust pipe will cause a slow exhaust flow, which will in turn give the gas plenty of time to cool off en route.

Yes mufflers do scavenge. But IMHO not as well as a properly tuned exhuast system (before the mufflers). If the headers are properly lengthed and sized for your application, pipe diam. is correct and the length is right then really the muffler is just merely aiding and not doing all the work. I prefer flowmasters because they are tried and true. You can show me numbers all day long......But I'll have some of my own to show you nonbelievers!

 

Considering other mufflers have been proven to produce more HP on the same engine a 406ci one. Aero more than some flows, and I believe 2 were listed above the aero.

 

Well mark, I think It really comes down to personal preference. Mufflers IMO are not what makes the horsepower. If you read my previous post you'll understand why (restriction would be the only differing variable). Not sure I've seen that 406 test but I doubt the power difference was all that great.

Later,

Brian

BTW- i didn't know the comps were shorties?? Are you sure they mailed him the right ones? If not then that picture is so damn misleading its not even funny. You only need full length, not long tubes.

 

You're right it was only like 6hp.

Yeah, I said i was gettin those, cause i thought they were long tubes.

 

WHAT?!?!

 

. LOL. ahh the ignorant fools are finally posting. Well buddy......show me the error of my ways. Or here's an idea.... SHUT THE F*CK UP!!

 

You're confused by density, mass and weight. The temperature of a gas has no effect on its mass or weight in a closed system. If you're thinking of the gas inside the fixed volume of the exhaust system, the change in mass due to the change in density is negligible.

 

Thats what I'm talking about. Colder air is denser air. SO......as the air cools it becomes denser (heavier taken as an implication here). Yes there is a change in mass. This would be the reason why people run cold air intakes. My previous post makes sense if you read it again. You still haven't pointed out where exactly I strayed from the truth. I could write a 10 page article on the characteristics of air flow and its negligable properties if you'd like! That qoute was a brief explanation as for why. I didn't give ALL the facts becuase this would have taken me 8 years to damn write. And well......I'm lazy too.


BTW- Sorry about the SHUT THE F*CK UP comment. It was drunkk andd I wa s late. LOL

 

no4njunk, you're overly simplifying and not making any sense with the whole cold air / density thing in the exhaust. Air in the exhaust has a constant mass no matter how hot or cold it is. If the exhaust cools, it doesn't magically grow more mass during transit. It has absolutely nothing to do wit the reason people run cold air intakes. In their case, they have a choice of whether to breathe cold dense air or hot less dense air (i.e. more air, or less air, mass). In the exhaust's case, you have a fixed mass of air with a certain heat and pressure, which leads to....

What you were trying to get at is energy. Energy = heat. Energy is also proportional to velocity. The exhaust's initial velocity depends on the pressure at the exhaust port and the pressure of the exhaust system (as was already covered) If you keep the exhaust hot, then energy is not leaving the system, so velocity also stays high. If the exhaust cools, energy is leaving the system, the exhaust slows down.
This is still simplistic, but IMO it makes the relationship clearer. I can assure you that nothing grows mass by cooling it. In fact, if you want to get REALLY technical, heating an object increases mass, and cooling decreases mass. You may be familiar with E=mc^2. Oh sure applying Einstein's theory to everyday life is ludicrous, but fact is, if you have an accurate enough balance, you can measure a fixed object's mass and observe it to increase exactly as that equation would predict. Energy has mass, and more energy weighs more than less energy.

 

I didn't mean to say that it grows in mass. BUT...you just proved that I was write. Cold air is denser and Hot air is less dense. You guys are just repeating what I initially stated. I'm not sure about the energy theory you have. The entropy law states that as energy changes states, it degrades. Now as it changes from heat to sound it will lose mass right?? according to your statement---

Which by the way totally contradicts what you wrote!!

The energy your refering to takes many different forms. Heat and sound are two. Now according to what you wrote if energy changes form then it changes in mass. BUT as it cools it becomes denser. Now denser air is KNOWN to be HEAVIER. How could you argue this? This in turn slows the speed (velocity) of the air down. This also causes a tumbling in the air path which leads us to........ Crappy flow! Yes it is a fixed system but you say that enery has mass right?? And that this doesn't apply in a fixed system. Well I'll look into this but I believe a little thing called pressure would totally counter that.

Go back and read what I first put!!!

 

You guys aren't debating the relationship between density and mass. You're disagreeing over the ways in which you view the exhaust gas as a system. It appears to me that No4NJunk has set up a control volume, in which mass or gas can enter the pipes in order to fill the volume created by the cooling exhaust gas. I think Ed, on the other hand, is viewing the exhaust system as a system in which the quantity of exhaust gas that we are looking at exists independant of it's surroundings at any given instant. Thus, the mass of the exhaust gasses inside the exhaust system remain constant as the temperature decreases. The result here (holding mass and volume constant while decreasing temperature) would be a decrease in pressure.

Anyways, maybe I've interpreted your arguments correctly, maybe not. I hope I have and that it will help reach a conclusion. I'd write some of my own thoughts on the topic, but am hungry and will have to save that for later...

MikeS

 

ME TO!!!!!! ME TO!!!!!!!

Let's not forget that another reason that you want to keep the exhaust gas temps high is due to molecular activity. The same reason a hot air balloon works. The higher the temp of the air, the more it "moves". Once the air in the balloon cools, it becomes less active. It’s the activity of the molecules that causes the balloon to rise.

The density is what changes, but there is no weight change. I’ll give you an example of another balloon.

Fill a regular ‘party’ balloon with your own air from your lungs. Next place it in a freezer for about 1 minute. The balloon will have appeared to ‘deflate’. That’s because the molecular activity has slowed and the air has become more dense. There is still the same amount of air in the balloon, but now it’s contracted. Once you take the balloon out and allow it to reach room temperature again, the air inside will become more active and will expand again. The weight of the air never changes.

And as far as the “scavenging” in a muffler, that’s bull crap. What happens is what they call ‘pulse wave tuning’. There is no scavenging going on. All that’s happening is the pulses (like you feel at the tailpipe) are used to create a low pressure zone (which is what was said and is correct), but that only lowers resistance to the following pulse wave. The only way to create scavenging is by merging two pulses into one.

And just to give you guys another helpful tip....... Always try to locate the exhaust tip(s) in an area under the car with a low pressure zone. This will further reduce the resistance in the exhaust system.

AJ

 

You said that when the exhaust is cold there's a larger mass of gas inside the exhaust system for the engine to push out.

 

I said what Apeiron??

 

Maybe you do need to take 8 years and 10 pages to explain youself.

 

"and he kicked him in the ding ding!!!!!" :sillylol:

AJ

 

lmao.

 

So where and how far under the car would you recomend for the exhaust tip so that they would be in this low pressure zone?

Ben

 

Whatever. If your gonna make stupid comments instead of providing relevant information then I'm not going to waste my time. You OBVIOUSLY don't know what your talking about. If the best you can do is misqoute me then maybe you shouldn't try so hard.

Hell.....I've had more intelligent conversations with retarded mutes!!

damn, I forgot that heavy is the same as large . Whats sad is, thats not even the only thing you missqouted.

 

i agree with no4njunk except that it is a physics principle that mass never changes. most people confuse the word mass with weight. think of it as pushing a 1 cubic foot piece of plastic versus pushing a one cubic foot rock. the plastic is less dense and will be easier to push. pushing cold air will be like pushing the rock.

 

thank you!! I couldn't have put it better myself. I knew I opened up pandoras box when I said that the mass changes. That was a slip up on my part. But originally that wasn't what I stated. A few on here got me a little side tracked. I was trying to state the temperature change in a fixed system such as an exhuast pipe directly affects the density. Now you can also take into account the energy loss through degradation because of entropy. But i won't get into that.....or maybe I already did.....oh well ....I probably halfassed it like I do everything else. Maybe I should write a 10 page 8 year book on it huh Apeiron?!?!

 

no4njunk, if that's wasn't the point of your comment, please tell me what was because it's unclear. I sympathize with the frustration you obviously feel over not being able to communicate your ideas clearly to others. If I'm really misunderstanding the intent of what you said, why not try to restate your thoughts instead of accusing everyone of ignorance who doesn't agree with you?

Let's imagine for a minute and see if we can come up with an estimate of how much mass there is in the exhaust of a car:

Pretend we had a theoretical car whose exhaust system was a 16' long piece of 3" pipe. The exhaust system would then have a volume of about 1357 cubic inches, or about 22.24 litres. Under standard conditions, 1 mole of molecules in gaseous state occupy about 22.4 litres. However, we know that the exhaust system is under pressure, otherwise the gas would never move. Let's say that it's under 2 atmospheres of absolute pressure, or roughly 30 PSI absolute. That seems a little high to me, most exhaust pressure gauges will only read to 15 PSI gauge, but that's ok it will only skew our results upwards. In that case, we'll have about 2 moles of gas inside the exhaust system. Of course our exhaust is hotter than standard conditions too, which as no4njunk has pointed out means that it will be less dense as well, but again this will only skew our results upwards. Let's also imagine that our car doesn't actually burn any gas, but only ejects raw unburned octane molecules in its exhaust. Octane has a molar mass of about 114 grams/mole. This is much higher than the molar masses of molecules that make up the majority of exhaust (diatomic nitrogen @ 28 g/mol, water @ 18 g/mol, carbon dioxide @ 44 g/mol, carbon monoxide @ 28 g/mol, and a smattering of other gases), which yet again means our estimate will be too high. Our theoretical car would have 228 grams of gas in its exhaust system. That's about 8 ounces of gas.

How much horsepower does it take to move that 8 ounces? Not a lot. How much more power will we make if we can reduce the mass of that gas to 6 ounces? or 4 ounces? Not a whole lot. The "little thing called pressure" is responsible for the losses in our exhaust, not mass.

My model is of course a gross over simplification that only took about 5 minutes of thought using high-school physics and totally ignores thermodynamic effects, but anyone may comment on it if they like.

 

Well if you actually wanted to go through the time and effort to find in, you need a special measuring device. I can't for the life of me remember what it's called right now, but I wanna say a manometer? I don't think that's right though.

Most of the low pressure zones under the car would be pretty obvious IMO. Like right behind something, or even next to something. You know how a lot of people would like to put side pipes on their car coming out at a 30* - 45* angle? That's a good spot also because the air rushing by the exhaust tip would cause a low pressure zone right behind the end of the tip. But behind the rear tire is better than in front of it because there's a high pressure zone right in front of the tire.

I attached a pic of that example as well as another of putting the tip just behind the axle, but you have to do it in a way that the air is being "sucked out" per se. Normally that would be just behind the axle.

Actually, out the back of the car is a pretty good place, but not the best. With the shape of the backs of our cars, there is actually a low pressure zone directly behind it at higher speeds, but there are better places under the car.

AJ

 

AJ

 

Nice drawing. I understand what you are saying, but I would think that would have minimal results though wouldnt it. Actually , thinking about it, as long as the tip pointed straight back and was under the car and not sticking back into some spot where the air is wraping around the back of the car or something it would put a low pressure zone behind the tip right. What I'm trying to say is it is going to block air from in front of it's self, and cause there to be a low pressure zone correct?

Ben

 

Yes. You're right. There would be a lower pressure zone directly behind the tips themselves. That's why I said that there are better ones under the car.

To me, this is one of those "don't overlook the obvious" things. I would have never even thought of this until I read a book by Smoky Yunick. He actually said that if you can find the right area, it will have similar effects of a super charger. I think he may have been exagerating a little, but then again, I have yet to see where the guy has made a sarcastic comment.

AJ

 

AJ, Do you know anything about x-pipe distance from the collectors? If so could you make a visit here? https://www.thirdgen.org/techbb2/sho...hreadid=142256

Ben

 

. Well I must have totally misinterpreted your posts. I had the impressioin that you were merely making snaps instead of posting like the previous post (which BTW makes a hell of a lot more sense, even though you didn't calculate the pipe thinkness *if we subtract out the thickness of the walls (because we want to know the inside area) 14 guage pipe- (.064") and subtract you area loss there). But none-the-less I agree. I was just trying to go from the view point of air density. Why I even included mass in my argument I don't know. I think someone tossed the word around and my dumba*s picked it up and said **"Hey, looky here, another COOL word!!"**. I still feel that my original statement stands true and that you and some others just missed the boat.

Now, you said mass doesn't change (change in amount) in a closed system which happens to be fact. BUT it does change in density. Lots of factors contribute to this. This mass changes state (as already mentioned 800 times now) by expanding (more pressure) and contracting (less pressure). Contracting (more dense and heavier) but still occupying the same space because there is a constant flow right?? What one "body" of gas can't provide the next fills thus creating pulses and flow. This would bring pressure in because as I mentioned exhaust gas pulses have a high pressure Front and a vacuum for a tail. This vacuum is what pulls (as already mentioned by me) while the high pressure front surges forward in an effort to equalize itself with a lower pressure area.