is a muffler good for your engine?
#11
11-22-2010, 09:07 PM
#12
11-22-2010, 09:55 PM
Nothing mentioned about "backpressure" in that blurb from wikipedia. I must find a bit of irony in your attempt at validating the whole "backpressure" thing...by using an internet source.
The problem with the internet is that there isn't an authority anywhere that makes sure CORRECT information is the only information ever "published" on any articles written on the internet. While I find no fault in what wiki says about scavenging, I do have a problem with false information being posted.
I have numerous dyno-proven instances where I have personally seen and been involved with the effects of backpressure and the positive results that have been awarded after getting rid of it. Yes, a certain amount of piping IS necessary for gains to be had across the board.....but to make the engine WORK to rid itself of exhaust is not the way to make power.
Besides, think of what you're getting at with the scavenging/backpressure claims....
How can an exhaust system that restricts flow have the ability to essentially "suck" more exhaust from the cylinders?
Just a friendly question....
The problem with the internet is that there isn't an authority anywhere that makes sure CORRECT information is the only information ever "published" on any articles written on the internet. While I find no fault in what wiki says about scavenging, I do have a problem with false information being posted.
I have numerous dyno-proven instances where I have personally seen and been involved with the effects of backpressure and the positive results that have been awarded after getting rid of it. Yes, a certain amount of piping IS necessary for gains to be had across the board.....but to make the engine WORK to rid itself of exhaust is not the way to make power.
Besides, think of what you're getting at with the scavenging/backpressure claims....
How can an exhaust system that restricts flow have the ability to essentially "suck" more exhaust from the cylinders?
Just a friendly question....
#13
11-22-2010, 10:10 PM
YES, backpressure WAS mentioned in the fact that exhaust design and diameter affects scavenging. Read again, Bucko.
http:// en.wikipedia. org/wiki/Manifold_%28automotive%29
If this doesn't butter your bread, I'm not sure what will? Do you want me to perform a telephonic recorded convo with Henry Ford or something?
So you mean to tell me, you've seen dyno test results of a gasser with a 20" exhaust pipe as compared to a 3" exhaust pipe, and there is ZERO performance differences?
It's not so much a "restriction" as it is an "imperative to a properly running motor".
Read the Scavenging section 3/4 to the bottom of the new page I presented. It elaborates a little better than I can.
Also, take note to the design in headers; haven't you ever wondered why gassers headers are so awkwardly designed? It's to help this scavenging effect
If reading that section doesn't explain everything, then quite frankly my friend, I'm not sure that Ferruccio Lamborghini could explain it himself.
http:// en.wikipedia. org/wiki/Manifold_%28automotive%29
If this doesn't butter your bread, I'm not sure what will? Do you want me to perform a telephonic recorded convo with Henry Ford or something?
So you mean to tell me, you've seen dyno test results of a gasser with a 20" exhaust pipe as compared to a 3" exhaust pipe, and there is ZERO performance differences?
It's not so much a "restriction" as it is an "imperative to a properly running motor".
Read the Scavenging section 3/4 to the bottom of the new page I presented. It elaborates a little better than I can.
Also, take note to the design in headers; haven't you ever wondered why gassers headers are so awkwardly designed? It's to help this scavenging effect
If reading that section doesn't explain everything, then quite frankly my friend, I'm not sure that Ferruccio Lamborghini could explain it himself.
Last edited by 85_305; 11-22-2010 at 10:12 PM.
#14
11-23-2010, 08:18 AM
Ok.....
So explain to me how we went from you saying, "Well yes, NA motors needs backpressure" to the subject of scavenging. Remember, you brought it up first. I am in no way disputing what you are getting at with scavenging because I have been somewhat (albeit not by myself) involved in quite a bit of exhaust tuning work and header design. I don't make a living at it, and I am not the end-all, be-all authority on the subject. At the same time, I am trying to tell you that the subject of "backpressure" (as it relates to internet "technical discussions") is a very misunderstood subject. Since we're on the subject of internet discussions, that is one subject that is always brought up where you get these internet experts that claim the more restriction your exhaust has, the more low end torque you make. These are the people that get the "internet forum facts" rolling and spreading like the birthrate in India.
The term "backpressure" means, in no more words, "restriction". If we're trying to make the engine as efficient as possible, then why would we want the engine to actually have to work harder to expel the spent gasses? Obviously, you want to have the smoothest, most free-flowing path for the exhaust to take; minimal amount of bends and abrupt transitions. Your example of 20" exhaust is a bit over-the-top as there is hardly any need for a production vehicle to have an exhaust of that size....and yes, at that point, the size of the pipe would become a problem, much the same way as open exhaust manifolds or headers create.
The problem comes when atmospheric pressure can force it's way back into the pipe between exhaust pulses (or in the case of the large sewer pipe, the pressure in the pipe from the exhaust is insufficient to maintain velocity against the atmospheric pressure). This is a situation that you want to avoid at all costs when designing an exhaust system because at that point, your lack of velocity is costing you power. Maybe this is where the term "backpressure" came from....I don't know. But it is a great example of a horrible misnomer.
My favorite example to use when talking about this subject is my friend Phil's 1966 Chevelle with a worn out 327 and TH350. When I say worn out, I mean 25-30% leakage past the rings worn out. It was tired. It had a nice set of equal-length, long tube headers that transitioned into a factory style dual exhaust with 2.5" pipe all the way to the rear of the car. Sure, the car ran pretty good and sounded very nice. He wanted a different exhaust and there wasn't a shop around that would put dual 3" pipes out the side that exited in front of the rear wheels. The shops didn't want to be responsible for making the car "lose low end torque". Ha ha. What a bunch of morons.....even the people that work with exhaust pipe for a living had accepted the blind "truth" that the engine needed "backpressure". My friend built his own. Should I tell you the before and after effects? Numbers mean very little to most people nowadays, so I will simply tell you that the carburetor required MAJOR jetting changes to run properly and the car would absolutely roast both back tires from a dead stop (no power-braking) when before the change it would require a ton of effort (and power-braking) to do the same thing.
The moral of the story is that in more instances than I care to think about, a group of guys have absolutely debunked any theories that backpressure is a necessity for making any kind of performance gain. Is there a limit? Of course there is. Are there simple rules to follow? Of course. My experience shows that a well-designed single exhaust will put to shame ANY dual exhaust you can think of simply because of SCAVENGING properties due to exhaust pulse flow. However, for most any street-driven, large displacement engine, 3" pipe is sufficient. It MAY be wise to enlarge the diameter to no more than 3.5" after the merging point, but only if it is a high performance application. Your Honda CRX isn't going to benefit from a 3" exhaust at all. There simply isn't enough exhaust VOLUME (talking quantity here, not loud fart cans) to maintain exhaust velocity in the pipe.
It is a balancing act. There are trade-offs between flow and velocity. The bottom line is that RESTRICTION (everyone's favorite term "backpressure") IS BAD. Any reduction of backpressure can do nothing but help....as long as you have a well designed length of pipe that safely and effectively routes the exhaust from the manifold to the rear of the vehicle while maintaining a high enough velocity to keep the exhaust from slowing too much on it's journey.
---AutoMerged DoublePost---
By the way, you do know that Wikipedia entries are not written by "professionals", but mere mortals such as you and I. The only changes that ever get made to the entries come from people who know more about it than most......
Otherwise Wikipedia entries are taken for gospel. Even if they're blatantly wrong.
So explain to me how we went from you saying, "Well yes, NA motors needs backpressure" to the subject of scavenging. Remember, you brought it up first. I am in no way disputing what you are getting at with scavenging because I have been somewhat (albeit not by myself) involved in quite a bit of exhaust tuning work and header design. I don't make a living at it, and I am not the end-all, be-all authority on the subject. At the same time, I am trying to tell you that the subject of "backpressure" (as it relates to internet "technical discussions") is a very misunderstood subject. Since we're on the subject of internet discussions, that is one subject that is always brought up where you get these internet experts that claim the more restriction your exhaust has, the more low end torque you make. These are the people that get the "internet forum facts" rolling and spreading like the birthrate in India.
The term "backpressure" means, in no more words, "restriction". If we're trying to make the engine as efficient as possible, then why would we want the engine to actually have to work harder to expel the spent gasses? Obviously, you want to have the smoothest, most free-flowing path for the exhaust to take; minimal amount of bends and abrupt transitions. Your example of 20" exhaust is a bit over-the-top as there is hardly any need for a production vehicle to have an exhaust of that size....and yes, at that point, the size of the pipe would become a problem, much the same way as open exhaust manifolds or headers create.
The problem comes when atmospheric pressure can force it's way back into the pipe between exhaust pulses (or in the case of the large sewer pipe, the pressure in the pipe from the exhaust is insufficient to maintain velocity against the atmospheric pressure). This is a situation that you want to avoid at all costs when designing an exhaust system because at that point, your lack of velocity is costing you power. Maybe this is where the term "backpressure" came from....I don't know. But it is a great example of a horrible misnomer.
My favorite example to use when talking about this subject is my friend Phil's 1966 Chevelle with a worn out 327 and TH350. When I say worn out, I mean 25-30% leakage past the rings worn out. It was tired. It had a nice set of equal-length, long tube headers that transitioned into a factory style dual exhaust with 2.5" pipe all the way to the rear of the car. Sure, the car ran pretty good and sounded very nice. He wanted a different exhaust and there wasn't a shop around that would put dual 3" pipes out the side that exited in front of the rear wheels. The shops didn't want to be responsible for making the car "lose low end torque". Ha ha. What a bunch of morons.....even the people that work with exhaust pipe for a living had accepted the blind "truth" that the engine needed "backpressure". My friend built his own. Should I tell you the before and after effects? Numbers mean very little to most people nowadays, so I will simply tell you that the carburetor required MAJOR jetting changes to run properly and the car would absolutely roast both back tires from a dead stop (no power-braking) when before the change it would require a ton of effort (and power-braking) to do the same thing.
The moral of the story is that in more instances than I care to think about, a group of guys have absolutely debunked any theories that backpressure is a necessity for making any kind of performance gain. Is there a limit? Of course there is. Are there simple rules to follow? Of course. My experience shows that a well-designed single exhaust will put to shame ANY dual exhaust you can think of simply because of SCAVENGING properties due to exhaust pulse flow. However, for most any street-driven, large displacement engine, 3" pipe is sufficient. It MAY be wise to enlarge the diameter to no more than 3.5" after the merging point, but only if it is a high performance application. Your Honda CRX isn't going to benefit from a 3" exhaust at all. There simply isn't enough exhaust VOLUME (talking quantity here, not loud fart cans) to maintain exhaust velocity in the pipe.
It is a balancing act. There are trade-offs between flow and velocity. The bottom line is that RESTRICTION (everyone's favorite term "backpressure") IS BAD. Any reduction of backpressure can do nothing but help....as long as you have a well designed length of pipe that safely and effectively routes the exhaust from the manifold to the rear of the vehicle while maintaining a high enough velocity to keep the exhaust from slowing too much on it's journey.
---AutoMerged DoublePost---
By the way, you do know that Wikipedia entries are not written by "professionals", but mere mortals such as you and I. The only changes that ever get made to the entries come from people who know more about it than most......
Otherwise Wikipedia entries are taken for gospel. Even if they're blatantly wrong.
Last edited by PHPDiesel; 11-23-2010 at 08:25 AM. Reason: Automerged Doublepost
#15
11-24-2010, 08:02 PM
well if you were to blow a saxaphone or clarinet you would know that back presure makes the reed resonate. so if the valve train is the reed and exaust blows through it un restricted it would tear the valve to bits so in my nonprofesional usumption valves need to have something to balence them out. ive seen a cummins dodge dog out with 4" pipes stacked off it blowing black smoke (aka wasted fule) and ive seen my 90 HP VW waste them with a mufler, im thinking that if the factory exaust is too restrictive the dum *** exaust of 4" pipes and wastefull chips is too egotistical but like i said im no expert and am here only to get ideas from other diesel lovers "dont hate" and please dont correct my spelling, im drunk
#16
11-25-2010, 03:34 AM
I've been split on the subject on the TDI. The only person I've seen that seems to know what they are talking about states that the stock turbo will overspeed without a muffler. Mine is straight piped and it sounds like it barks, I guess it just sounds too cool to worry about it. Supposidly aftermarket turbos don't have the problem, which wouldn't surprise me. The whole car is designed so well out of the factory IMO that your making compromises on pretty much antything you do.
Check out tdiforum.
Check out tdiforum.
#17
11-25-2010, 09:33 AM
well if you were to blow a saxaphone or clarinet you would know that back presure makes the reed resonate. so if the valve train is the reed and exaust blows through it un restricted it would tear the valve to bits so in my nonprofesional usumption valves need to have something to balence them out
The scavenging affect is DERIVED from exhaust backpressure. End of story.
I've been split on the subject on the TDI. The only person I've seen that seems to know what they are talking about states that the stock turbo will overspeed without a muffler. Mine is straight piped and it sounds like it barks, I guess it just sounds too cool to worry about it. Supposidly aftermarket turbos don't have the problem, which wouldn't surprise me. The whole car is designed so well out of the factory IMO that your making compromises on pretty much antything you do.
Check out tdiforum.
Check out tdiforum.
EDIT: Just saw you are on tdi forum. Dunno what the hell that is, but go to tdiclub. Thats THE place to go for TDI's Bud.
#19
11-25-2010, 11:44 AM
Diesel Bomber
silly bobcat
