exhaust knowledge

[jdm92_accorn]

if anyone is interested, if your car is daily driven and you want to get good gas mielage and performance the best exhaust to use is a 4-2-1 header, 2.25" mandrel bent piping, stock converter and a high flow "chambered muffler". best i found to use is a 3 chamber one like flowmaster 60 series or a magnaflow or the obx dtm with the 2" tips. just make sure when you look into the converter you can see strait through the honeycomb, make sure its not clogged. if it is replace it. the "high flow" converters are more less a hollowed out resonator. if you hollow out a converter you will loose too much back pressure and prematurely wear out seals. you ever notice these old cars with strait pipes start to smoke like freight trains then soon after give up. thats because like the man said you need a certain amount of backpressure to keep everything together. about 1lb of back pressure is the bare minimum for a street driven car. and that is even more serious for stock f22 owners because of our low compression ratio( 8.8:1 ). if you use the setup i described above on an f22a1 it makes a hell of a diference in acceleration. personally i used an ebay 4-2-1 header, ebay 2.25" catback exhaust i took the canister off sold it to a kid with a civic then ordered an obx dual 2" tip muffler and a 16" resonator and took it to a local muffler shop and had him weld the muffler on and put the resonator after the first 90 deg bend in the pipe and used the stock converter.

[owequitit]

if anyone is interested, if your car is daily driven and you want to get good gas mielage and performance the best exhaust to use is a 4-2-1 header, 2.25" mandrel bent piping, stock converter and a high flow "chambered muffler". best i found to use is a 3 chamber one like flowmaster 60 series or a magnaflow or the obx dtm with the 2" tips. just make sure when you look into the converter you can see strait through the honeycomb, make sure its not clogged. if it is replace it. the "high flow" converters are more less a hollowed out resonator. if you hollow out a converter you will loose too much back pressure and prematurely wear out seals. you ever notice these old cars with strait pipes start to smoke like freight trains then soon after give up. thats because like the man said you need a certain amount of backpressure to keep everything together. about 1lb of back pressure is the bare minimum for a street driven car. and that is even more serious for stock f22 owners because of our low compression ratio( 8.8:1 ). if you use the setup i described above on an f22a1 it makes a hell of a diference in acceleration. personally i used an ebay 4-2-1 header, ebay 2.25" catback exhaust i took the canister off sold it to a kid with a civic then ordered an obx dual 2" tip muffler and a 16" resonator and took it to a local muffler shop and had him weld the muffler on and put the resonator after the first 90 deg bend in the pipe and used the stock converter.

Cite your sources. The exhaust system and associated size is highly dependent on the engine. Not the other way around.

Also, I have NEVER seen any evidence of an exhaust system having anything to do with an engine failure, unless it was way too short and the exhaust valves burned.

It was much more likely a failure due to abuse, neglect, or just plain poor manufacturing tolerances.

Everything here is blatantly false.

[deevergote]

You don't need backpressure.

You want flow velocity.

End of story.


The key to making a performance exhaust system is to get as much exhaust gas out of the engine as possible, as quickly as possible. Piping that is too large will create stagnation and turbulence. Enough of that will result in reversion. Too small... well... that one should be obvious.
Noise reduction, fitment, and emissions are where the tradeoffs happen. You can't legally run a car that makes too much noise. Many tracks won't even allow an unmuffled car (especially on "street nights"). To be emissions legal, you need a catalytic converter. Many people remove them. I, personally, like breathing clean air... and the 1-2hp that I lose by having a cat doesn't kill me. And, of course, you can't really run a straight pipe to the back of the car, so you have to bend the pipes.

[PakaloloHonda]

I'm just gonna mark my spot in this thread like an old dog ..

As I'm just gettin ready myself to install a DC Sports Header, a cat (I removed it a few years back)
and hopefully retain my 2 resonators, along with a new MagnaFlow double tip muffler.
My Ractive double tip has just started to show signs of fatigue (small hole)
and while I'm havin the cat installed for *legal* purposes, I thought it'd be great
to do all this work at once ..

Interesting opinions here (as usual) I'd like to see where this all goes ..

A Hui Hou !!!
Tomi

[Accrdwgnguy]

high flow cat

if you want a high flow cat or just need a new one Random Technology is the way to go http://www.randomtechnology.com/honda.html They even make a direct fit for our cars. It's a real cat too, which means they are around 300, haven't priced them yet tho.

[johnl]

Before anyone starts reading the following stream of consciousness be warned that it became quite long without my really intending it to be so (I just kept typing as it came to me!). I'm no expert on exhaust system dynamics and make no claims to be one, so bear this in mind before you flame me for any errors in my understanding, I’m doing my best! I’m sure that the info that has been provided in this thread has been provided with the best of intentions, but according to what I think I do know about exhaust systems etc, I think there is at least some incorrect information being disseminated (at least some of what I can actually decipher).

As I understand it; back-pressure never gives more power (with the possible exception of divergent cone two stroke pipes, but we’re not considering two stroke applications), it is always counter productive in and of itself, though it might in some instances be associated with changes that do have a significant affect on engine power.

Testing has been performed (please don't ask me for my sources as I can't recall, stuff I've read in more than one place, from memory I think there's an interesting thread on back pressure on the Eng-Tips.com automotive engineering forum for one) where restrictor plates were placed in the exhaust, the only affect of which was to increase or decrease back pressure depending on the size of the deliberate restriction.

In these tests on given exhaust systems, increased back pressure always resulted in less power across the rpm range.

The more gas pressure there is in the exhaust port as the exhaust valve opens the more difficult it is for the higher pressure exhaust gas to escape the combustion chamber, and this is the case regardless of rpm or throttle opening or whatever. It's simple physics, the more equal two differential gas pressures are, the harder / slower it will be for the higher pressure gas to move into an area of lower gas pressure.

Pressures in exhaust systems comes from two sources, the first being back pressure that is simply high pressure gas trying to escape from an enclosed space, creating a changeable 'ambient' pressure within the pipes that may vary in different parts of the system depending upon where exactly any restrictions lie, and on the 'compressibility’ of the gas, meaning that a high pressure can start at one end but take some time to be seen further down the pipe. Back pressure will be lower the larger the ID of any pipes in the system may be, and the less other restrictions there are. Back pressure makes it harder for exhaust gasses to exit the combustion chamber.

The second is positive and negative harmonic pressure waves that pulse up and down the pipes at more or less the speed of sound (negative pressure waves traveling at slightly less than the nominal speed of sound, positive waves slightly faster then the speed of sound). These pressure waves create mobile localized areas of positive and negative pressure that pulse up and down the exhaust system, both toward the end of the exhaust and ‘reflected’ back toward the exhaust valve. Negative pressure makes it easier for gasses to exit the combustion chamber.

A negative pressure wave traveling back up the pipe is created when a positive wave traveling down the pipe encounters an abrupt increase in the ID of the pipe, ‘reflecting’ a negative wave in the reverse direction. A positive wave traveling back up the pipe is created when the ID of the pipe abruptly decreases significantly, or some obstruction such as a muffler etc is encountered, reflecting some % of the wave back up the pipe.

These pressure waves are more or less independent of ‘ambient’ back pressure, though higher or lower back pressure may cause a slight change in the speed of the waves, with more back pressure meaning a slight (i.e. ‘slight’) increase in wave speed, and the reverse for less back pressure (the pressures involved with back pressure simply aren’t great enough to make a significant difference to the pressure wave speed, though F1 engine designers et al may well take it into account).

An overly large pipe diameter decreases the strength of the returning negative pressure wave, largely because it decreases the strength of the original positive wave (same energy in a larger space), so if the pipe is too big in ID then even though back pressure will be less the affect of harmonic waves on exhaust scavenging will be less, so less power may be produced in all parts of the rev range at which the scavenging affect of the negative pressure waves would otherwise be increasing power (i.e. the effect will still exist just not as strongly as with a more correctly dimensioned pipe).

Pipe lengths don't affect the speed of these pressure waves, but do affect how long it takes for the wave to reach the end of a particular length of pipe where it encounters a significant increase in pipe diameter and as a result is 'reflected' back toward its source as a negative of the original wave. This source is the open(ing) exhaust valve, and if the length of the pipe is X then the reflected negative pressure wave (creating a localized lower pressure as it passes back up the pipe) will arrive at the exhaust valve just as it's opening again and make it easier for the next shot of exhaust gas to exit the combustion chamber, and also for the exiting exhaust gas to 'suck' in more incoming mixture into the chamber (which then in turns allows a bigger bang with more power).

Some fresh intake mixture will typically be lost out the pipe when the exhaust gas is effectively ‘sucked’ out of the exhaust port (keeping in mind that ‘suction’ as such doesn’t really exist and is only used because it can be a convenient term) and ‘pulls’ extra intake mixture in it’s wake (more so with greater valve overlap). However if we’re really lucky we can sometimes have a returning positive pressure wave ‘push’ at least some of that ‘lost’ mixture back into the combustion chamber just before the exhaust valve closes.

=============

Seems I've bumped up against the allowable limit for a single post, so here ends chapter one, chapter two to follow...

[johnl]

Chapter two:

Tuned length headers work by optimizing harmonic pressure waves in different parts of the rpm range (i.e. how short or long the intervals are between the exhaust valve closing and opening). If the pipes are too long this tends to excessively lower the rpm range at which it’s beneficial (because the negative wave will arrive back at the exhaust valve later, so as the valve opens it needs to also be opening later, which is what happens at lower rpm), so you can lose top end power. Note that this isn't because the back pressure is too low, it's because the harmonic frequency of the pipe is too low. Or, if the pipes are too big the pressure wave is too weak.

If the header pipes are too short then the reflected negative wave will arrive at the exhaust valve very quickly, and you need to be at very high rpm for this to arrive at the valve at the correct time. This might not be a problem if the engine is set up for and typically used at very high rpm, but if not then the pipe will be beneficial only outside the usable range of the engine.

It's a myth that using a too large diameter header (or pipe or muffler) causes a loss of performance due to a decrease in back pressure, if such a result occurs then it's a loss in pressure wave strength that will be responsible. This is also the case for the single pipe after the headers because this pipe also has an affect on system harmonics, though to a lesser degree than the header pipes do.

'Tuned length' headers (and there’s no real point in them if they aren’t ‘tuned length’, unless it’s just to decrease the affect of a restrictive manifold) can give improved power over a wide rpm range or a narrow rpm range, depending on the design of the headers. Longer header pipes will tend to give better power at lower rpm, shorter at higher rpm.

A given header can give improved power in a particular part of the rev range, but can also have adverse affects in the parts of the rev range where it's not having a beneficial affect, i.e. rather than a negative pressure wave arriving at the exhaust valve as it's opening (helping higher pressure escape the combustion chamber), a positive pressure wave can arrive, making it harder for the exhaust gas to escape the combustion chamber (hence less power because less intake can then be drawn in). It’s just lucky that returning positive pressure waves tend to be not as strong as returning negative waves.

Many stock (usually cast iron) headers tend to have primary pipes so short they do nothing for power at any particular useable part of the rpm range, especially 'log' style manifolds with very short primary pipes, but also tend to not be 'peaky' because they produce no pronounced enhancement at any particular point in the rev range (or maybe at revs the engine will never see in it’s wildest nightmares). Very short branches on headers also tend to increase 'interference' from one cylinder to another, meaning that unwanted strong positive pressure wave pulses can transfer from one exhaust port to another, longer branches tend to lessen such interference.

Stock cast ‘header’ manifolds also tend to be less than ideal when it comes to the radius of bends etc. i.e. some bends tend to be too tight which caused an effective restriction in the manifold. Some stock cast manifolds are reasonably OK in this regard, Honda manifolds aren’t bad as these things go.

'Four into one' headers tend to give a 'peaky' power increase, just where in the rpm range depending on the length of the primary pipes (generally more suitable for racing than street). 'Four into two into one' tend to give a power increase over a wider rpm range, again the specifics depending on the lengths of the pipes involved (generally more suitable for 'performance' street applications).

'Four into one' headers have one point at which the positive exhaust wave encounters a significant increase in pipe size (at the ‘collector’), and this limits the range of rpm at which the header will be effective. 'Four into two into one' headers have two points at which the gas encounters a significant diameter increase (at the first ‘two into one’ collector, and again some distance down the header at the second 'two into one' collector), and this spreads the range of rpm at which the header is effective, though it generally lessens the strength of the affect compared to the ‘four into one’ header.

Both styles of header can improve power in different ways even if their back pressure is identical, i.e. the back pressure isn't responsible for how the headers work, the harmonic frequency is. The only requirement is that back pressure not be excessive or engine breathing will be adversely affected, and possibly not just at higher rpm. The ideal header will have little back pressure but not be so big that the strength of harmonic waves is diminished.

Fitting an improved exhaust doesn't 'require' improving induction, you can get a worthwhile power increase with exhaust without touching the induction system. However the improved induction may work better with improved exhaust insofar as for best results the exhaust, induction and cam timing need to be optimised to all work together in the rpm range at which the engine will be mostly used. It’s all interconnected, and bloody complex!

To the best of my knowledge lack of back pressure can't hurt "seals", by which I assume the original poster means head gasket, piston rings and maybe valves and valve seats (?). It may be that rings etc can fail not long after an exhaust system has been upgraded, but this is most likely due to the engine already being marginal and the driver now taking advantage of the better breathing provided by the improved exhaust (read higher rpm, more lead-footing, i.e. more 'fun').

Feel free to correct any errors you (whoever) feel I may have made, but please supply reasons for any disagreement.

[deevergote]

Good stuff, John... and as far as my own studies go, every word of it seems correct. I'm no expert either, but it's good when educated amateur knowledge coincides.



The best way to look at the entire engine is that it's an air pump. You want to be able to flow as much air through the engine as efficiently as possible. The whole idea of fuel and combustion complicates this a bit, as well as the mechanical efficiency of the engine and transmission... but overall, in it's simplest form, the engine is an air pump.

The F22A's largest restriction in stock form is the exhaust. Mainly because a narrow exhaust promotes low-end power. That's a trick used by the makers of small engines to give the illusion of a torquier (is that a word? ) engine. Opening up the exhaust allows for more power, and opening up the exhaust ports is the most important thing to do when modifying an F22A cylinder head (if you're on a budget, that's the part to do).


Reversion is when the spent gasses push their way back into the combustion chamber due to strong backpressure. Never good.

Stagnation can occur with TOO wide of an exhaust system. Think of it as a wide hallway with people standing around talking on either side... The hallway might be wide, but it's wide enough for people to gather and hang out "out of the way"... when a crowd of people that would nearly fill the hallway wants to come running through, it's not going to work! That wide hallway, thanks to it's size accommodating so many idle people, seems to be a much more narrow space than it really is! This creates a good deal of turbulence as well... which leads to increased backpressure.



I'm just adding on to what John said above. Exhaust theory isn't difficult in the beginning stages. When you get to sound waves, pressure changes, and all that crazy stuff, THEN it gets beyond my knowledge.

[owequitit]

Good stuff, John... and as far as my own studies go, every word of it seems correct. I'm no expert either, but it's good when educated amateur knowledge coincides.



The best way to look at the entire engine is that it's an air pump. You want to be able to flow as much air through the engine as efficiently as possible. The whole idea of fuel and combustion complicates this a bit, as well as the mechanical efficiency of the engine and transmission... but overall, in it's simplest form, the engine is an air pump.

The F22A's largest restriction in stock form is the exhaust. Mainly because a narrow exhaust promotes low-end power. That's a trick used by the makers of small engines to give the illusion of a torquier (is that a word? ) engine. Opening up the exhaust allows for more power, and opening up the exhaust ports is the most important thing to do when modifying an F22A cylinder head (if you're on a budget, that's the part to do).


Reversion is when the spent gasses push their way back into the combustion chamber due to strong backpressure. Never good.

Stagnation can occur with TOO wide of an exhaust system. Think of it as a wide hallway with people standing around talking on either side... The hallway might be wide, but it's wide enough for people to gather and hang out "out of the way"... when a crowd of people that would nearly fill the hallway wants to come running through, it's not going to work! That wide hallway, thanks to it's size accommodating so many idle people, seems to be a much more narrow space than it really is! This creates a good deal of turbulence as well... which leads to increased backpressure.



I'm just adding on to what John said above. Exhaust theory isn't difficult in the beginning stages. When you get to sound waves, pressure changes, and all that crazy stuff, THEN it gets beyond my knowledge.

It also restricts noise, which is something Granny doesn't want to hear.

That is why on a lot of high performance cars, there have been "dual stage" exhaust systems. At low RPM's the system is relatively restrictive, and at high RPM's, a valve opens and the exhaust becomes more free flowing. The Corvette Z06 and Mitsubishi 3000GT are good examples.

I think the new 190HP Accord I4 has one too.

Overall, I thought the information was on the details too. Obviously, it COULD go to a much more complex level, but overall it was awesome for the enthusiast.

[Camurai]

I'm not claiming to be an expert either, but to the best of my understanding, an exhaust can reach a point where it is so high-flowing that it will begin to draw unspent air/fuel mixture out the exhaust valve during overlap, resulting in reduced fuel mileage. Then again, at the level where that is likely to occur, fuel mileage isn't very likely to be at the top of the builder's list of priorities.

[12gage]

eversion is when the spent gasses push their way back into the combustion chamber due to strong backpressure. Never good.

which is why we stick large objects in peoples mufflers.

[Aeromech]

Random Tech CAT price

just thought I would add this since it was talked about before...

oh yeah this is directed to the original poster.... I was wondering what engine seals would be effected by having an incorrect exhaust setup? I really don't understand this claim.

The tech info in this thread is great stuff.

[verderacer]

Thats not always true. Large piping can cause lag and reduce flow efficiency. The science of aero, fluid and thermo dynamics is pretty specific. There is some good info for those who care to read.

http://www.sciencedirect.com/science/journal/0022460X
http://gltrs.grc.nasa.gov/Citations.aspx?id=1692
http://www.nsxprime.com/FAQ/Miscella...austtheory.htm

I had a great link to JPL's low speed dynamics abstract with resonance calculations but they took it down :-(

turbo setup? bigger is better, but you only have so much room. same rules for quiet apply.

there you go

[Accrdwgnguy]

Uh yeah having a gutted cat is going to do nothing bad to your engine. My Dad gutted the cat on his 87 CRX si 10 years ago, and drove it for 65,000 miles with no engine problems. (and 45+ mpg!) Now as for rust, well yeah....
But anyways, you want some real exhaust knowledge, look up David Vizard. http://www.superchevy.com/technical/...exh/index.html He knows what he's talking about. This article is aimed toward chevy V8's, but can be applied universally. And I would just like to add for Johnny Pipes there, Black smoke is from running rich, its unburned gas. Blue Smoke is burned oil, which you would see if your piston rings, valve seals or guides were bad. And white smoke is water.

[NAiL05]

It also restricts noise, which is something Granny doesn't want to hear.

That is why on a lot of high performance cars, there have been "dual stage" exhaust systems. At low RPM's the system is relatively restrictive, and at high RPM's, a valve opens and the exhaust becomes more free flowing. The Corvette Z06 and Mitsubishi 3000GT are good examples.

I think the new 190HP Accord I4 has one too.

Overall, I thought the information was on the details too. Obviously, it COULD go to a much more complex level, but overall it was awesome for the enthusiast.

Ferrari, Lamborghini, Porsche (some aftermarket exhausts) and a few other high end cars have been using the valve technology for quite a while also just to add to the list.