My Exhaust Muffler Theory, Just thought I might share... 56K BEWARE. Options

[ExSane]

Ok, here is my theory on exhaust mufflers. Basically this... faster exhaust goes out the faster air comes in. Lesser back pressure, the better the exhaust flow. The better the faster the exhaust flow, the better the gains. Here are the designs I used to conclude this theory.



HKS, Apexi N1 type mufflers - Becuz of the design and the edge of the canister is kinda sharp tipped, there maybe a little back pressure on the air flow. HKS Hi-Power has rather a large canister (larger than N1) and can cause a 'slight' back pressure depending on the output of fuel pulses coming from the engine. The stronger and faster the pulses, the less to worry about it. That's probably why most of these mufflers are used for Turbo's. Besides that, people just go for looks with these.

Otto Racing, Blitz type mufflers - The canister designs on these type of mufflers are curved into the tip pipe causing straight through exhaust flow. I don't even think there is any back pressure on this type of muffler design. Everything is pretty much straight through design. I think this is probably the best choice for N/A engines.

Greddy SP, Magnaflow type mufflers - This type of design is known to increase horsepower without ruining the stock look. The only difference between this muffler and the stock one is the piping size. The inlet/outlet diameters are bigger causing a little bit more flow. As you can see up in that picture, there are a lot of back pressure and restrictions made to air flow. This could also be the reason why this muffler isn't that loud and is slightly louder than stock.

Greddy EVO, OBX (EVO wannabe) type mufflers - Now this is an interesting design. From the looks of it, this muffler is design to have no back pressure. But considering the fact that it isn't straight through design, there might be a very slight back pressure on the exhaust flow. I haven't seen anyone with this muffler on at the races but I bet you this muffler will probably be a good add to performance as well as different.

Stock type mufflers - As you can see pictures, the piping for this type of muffler is rather small and they restrict fuel pulses in your exhaust. Back pressure is pretty heavy with this muffler and is probably why you feel so much gain when you take this thing out. As I said about my theory, "faster exhaust goes out the faster air comes in". Basically your engine breathes faster and farts faster. Your heart will beat faster. And then your legs will run faster. LoL. Metaphorically speaking...

Straight Piping type mufflers - Ahhh one of my most interesting ones. This is design is just pretty much straight through design without canister filteration which means no back pressure what so ever. Probably one of the best for choices for 6 cylinders and over. Thus reason being GT mustangs become so freakin quick with this mod. A 2002 Honda Civic EX VTEC coupe burned me and a V6 Firebird (I think stock) out of the streets with his straight pipe. And to think I kept up with that Firebird. The civic sounded like a damn muscle car. Probably one of my most interesting races I've experienced at the street race meets.

So, what you guys think???

This post has been edited by ExSane: Aug 10, 2006 - 12:33 AM

[WH95TE]

So you're saying we should get straight pipes?

I have stock and its lame

[ExSane]

So you're saying we should get straight pipes?

I have stock and its lame

I'm saying Straight Pipe is probably the best choice for 6 cylinders and up. For big size engines. Not small ones like ours.

[vsideboy]

I think you need some back pressure when you've got a turbo engine too?

[soulshadow]

Really with an O2 sensor and all, a straight pipe is fast because it does BURN more fuel and at the same time create power.

My theory, try going straight pipe on a Toyota camry for a month and you will see that your Miles/Gallon ratio has plummeth.

[Bitter]

i have no rear muffler and my milage is just as good as it was with it. from the middle resonator on back its just a pipe.

[playr158]

turbo motors need no back pressure...i run open down pipe daily

[easternpiro1]

interesting turbo motors dont need back pressure plyr? why not? i always thougth they didi have straight pipe (on my 7a). i took off a cat and the resonator...sounds sweet...wonder what it would soundlike with the 3sgte motor on?

[CelicaGT04]

Well i thought i knew that SOME back pressure was needed for N/A cars. I apparently thought that having straight pipe on a N/A motor would= loss of low end torque(which it might do). But as i read a topic on a forum, i read that the only thing that back pressure really does is lower the turbulance. It can, if you do not upgrade your fuel system burn your exhaust valves. But then again that wont happen after the first week, or month of having it. Turbo cars would not need back pressure as you are trying to release the air/fuel as quickly as possible.

"basically, theres 2 parts to the equation of airflow, both intake and exhaust- backpressure and velocity. backpressure is always bad. ideally an i/c engine wants no backpressure. however, as most people know, slapping a 3" exhaust on a stock motor generally hurts low end torque... this is thanks to our friend, velocity. air is a fluid, it has fluid properties. if you know what a syphon is, then thats exactly how the intake and exhaust colums of air work. the faster the column is moving, the more air is sucked in the intake using that vaccume, and the more is pulled out on the exhaust. ideally, you want very high velocity with very low backpressure. obviously this is pretty impossible to achieve across the rev range, as the airflow varies widely in its volume and velocity from idle to redline. choosing an exhaust/header/intake/ intake manifold/cams/head port that all work together to put that mix of velocity and backpressure where you want the maximum gain."

this is quoted from a guy on a forum.

I think i have it understood. Hope i am of some service.

This post has been edited by CelicaGT04: Aug 10, 2006 - 1:02 PM

[bufferdan]

I have a theory...put a potatoe in your exhaust and clog it up...then you get infinite amounts of power cause it never comes out and doubles the power everytime it recirculates through the engine

[playr158]

I have a theory...put a potatoe in your exhaust and clog it up...then you get infinite amounts of power cause it never comes out and doubles the power everytime it recirculates through the engine

that was so productive?!

boosted cars don't need back pressure like N/As do because N/A motors use back pressure for scavanging of exhaust gas

This post has been edited by playr158: Aug 10, 2006 - 2:14 PM

[orvillescelica]

Turbo'd motors (if they need back pressure or not) create more back pressure than an NA. this is because you are trying to push a larger volume of air through an outlet (exhaust mani, pipes, etc...) that is not too much bigger than NA stock no matter what you replace it with. Its simply a matter of choking. Well, not really since its all subsonic, its just mass flow restriction. Then again, you dont want an open to atmo set up either, since that would literally eliminate the needed exhaust velocity required to keep everything moving along.

Anyway, your theories on mufflers do not take into account the inside filters, fins and channels within the muffler that are there to eliminate resonace. I am not familiar with most of your brand mufflers, but i know most of them, though they are straight through designs, have complex inerts which aid in eliminating resonance and noise while preserving performance. There is a lot of engineering and design that goes into these mufflers to give you the best performance while staying either race or street legal. I for one would trust them.

[puretone]

expanding gasses (like in a chamber of the exhaust canister...) lose pressure and more importantly heat.

the expanding/cooling gasses thus also drop the back pressure....just like the case with a log-manifold and real built long-runners manifold that has a dedicated runner per cylinder.....

the spent gasses coming out of the chambers (that are still expanding as they enter the exhaust manifold...) and expanding into the manifold as they keep burning also create some vacuum (behind their expansion...) as they move thru, which is also a good thing for NA motors...

turbo motors just need as little restriction as possible, because of the low compression and that its up to the turbo to "feed" the motor the air it needs, so if you make it hard for the turbo to spool up by adding lots of back pressure it will slow the turbo from spooling......the same still-expanding gasses that leave the engine and head into the manifold are also the same still-expanding gasses that help spin up the turbo better.

now it all depends on the engine's volume of course, so say a 1,5 liter engine with a good back pressure exhaust thats built for a 4liter engine would have no effect because the entire volume of the 4liter exhaust is way more volume than a 1.5 liter engine can ever fill up efficiently to build its back pressure correctly....

[x_itchy_b_x]

uh, the best mufller is no muffler. the faster you eject air the faster the motor can injest air. the more flow the better...

[Bitter]

uh, the best mufller is no muffler. the faster you eject air the faster the motor can injest air. the more flow the better...

the best muffler is a turbo

This post has been edited by Bitter: Aug 10, 2006 - 11:57 PM

[puretone]

the best muffler is a turbo

i concur, the gods have spoken!