View Poll Results: Flowmaster restricts more than stock muffler?

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Flowmaster Restricts more than stock?

This is a discussion on Flowmaster Restricts more than stock? within the External Engine forums, part of the LSx Technical Help Section category; Originally Posted by nhraformula reminds me of a garbage truck Reminds me of a farm truck...

  1. #61
    Just me Y2KPewterSS's Avatar
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    Quote Originally Posted by nhraformula View Post
    reminds me of a garbage truck
    Reminds me of a farm truck

  2. #62
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    Quote Originally Posted by nhraformula View Post
    reminds me of a garbage truck
    an aftermarket catback for our cars makes our exhaust quiet and the sound of a large turbo?

  3. #63
    member since may 2000 nhraformula's Avatar
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    Quote Originally Posted by Speed Psychosis View Post
    an aftermarket catback for our cars makes our exhaust quiet and the sound of a large turbo?
    no, it sounds unrefined. its just loud
    2000 nhra edition formula
    a few bolt ons, 379 rwhp
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  4. #64
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    Quote Originally Posted by nhraformula View Post
    no, it sounds unrefined. its just loud

    thats why i love my magnaflow..very refined but can be a loudmouth when i get on it.

  5. #65
    NIUK! NIUK!..WOO!WOO!WOO! LIGHTNINGMCQUEEN's Avatar
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    Quote Originally Posted by nhraformula View Post
    when you have headers and off road pipe, i dont see how anybody can say its like stock.

    Well thats different. I was commenting on the muffler its self with out any other add ons.

  6. #66
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    2 cent time.
    Mufflers primary job......
    -control sound (thats why its called a muffler)
    -Create some sort of back pressure
    ....... mission complete

  7. #67
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    Quote Originally Posted by JoshuaGrooms83 View Post
    2 cent time.
    Mufflers primary job......
    -control sound (thats why its called a muffler)
    -Create some sort of back pressure
    ....... mission complete
    backpressure is a myth..exhuast is all about scavaging..gmhtp and every major exhaust company said so.

  8. #68
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    ^ porsche and ferrari say otherwise. you need some pressure. open headers does make you loose power. but the piping itself does a good enough job. you don't need a restrictive cat or muffler. and although a variable exhaust would be better, we already have so much low end it doesn't matter. thats for the engines built for high rpms that don't have much power in the low.

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    well this is what gmhtp said and i have to agree...in a exhaust system ..you want the spent fumes to be exited from the system as fast as possible..so why would you want backpressure ? also on the open header part they say run the headers a little farther out ..the lost can be attributed to the exhaust fumes not smoothing out ..so they dont flow as well. i dont know though...i'm no exhaust expert..but if gmhtp and magnaflow ect tell me backpressure is a myth and not need then i shall believe them.

  10. #70
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    Quote Originally Posted by shady milkman View Post
    backpressure is a myth..exhuast is all about scavaging..gmhtp and every major exhaust company said so.
    Whomever told you backpressure was a myth...lied to you! Different exhaust setups undoubtedly will alter low-speed grunt.

  11. #71
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    Quote Originally Posted by N20LT4 View Post
    Whomever told you backpressure was a myth...lied to you! Different exhaust setups undoubtedly will alter low-speed grunt.
    they said that has to do with the savaging..different exhausts have different scavaging points/levels..so some header/exhaust will have more low-end grunt compared to others.

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    Quote Originally Posted by shady milkman View Post
    they said that has to do with the savaging..different exhausts have different scavaging points/levels..so some header/exhaust will have more low-end grunt compared to others.
    yes, I agree with that theory, but at the same time from experience you can and will alter the low-end power, atleast in the case of running open headers vs. a closed exhaust. Not to say you won't gain any...in most cases you actually gain more power up top, but you will lose some low-speed pull.

  13. #73
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    this is a writeup i found take it with a grain of salt. but it backs up gmhtp and the exhaust manufacturers' statments ..sorry for the long read


    There is a common misconception that engines need backpressure in order to run properly, generate low end torque, etc. That is simply untrue. Backpressure is a bad thing. Always. Take a look at a top fuel dragster...how much backpressure do you think those zoomie headers make? Very little, and those engines produce 6500 hp.

    So, what is backpressure? Any fluid flowing through a pipe experiences drag on the walls of the pipe. This depends on a number of factors, including the diameter of the pipe, the smoothness of the inside of the pipe, the viscosity of the fluid, and the velocity of the fluid. This drag results in a pressure drop through the pipe. In order for the fluid to flow at all, the pressure on one end of the pipe must be higher than at the other. In an exhaust system, that pressure drop is what we refer to as backpressure. It's pretty obvious that the engine has to produce this pressure differential, so the less power it has to spend making pressure to push the exhaust out, the more power it can send to the wheels.

    Given that exhaust pipes are pretty smooth, and that we can't change the viscosity (thickness) of the waste gas being forced through the pipes, we are left with basically 2 parameters we can have any control over: The pipe diameter and the gas velocity.

    Unfortunately, the pipe diameter controls the gas velocity since the volume of gas is prescribed by the engine. So, we really only have one thing we can change. So, bigger pipes allow less pressure drop for a given volume of gas because the velocity is lower. The pressure drop (backpressure increase) is proportional the gas velocity squared, so if I double the gas velocity (by reducing the cross sectional area of the exhaust pipe by half) then I quadruple the pressure drop.

    Well, there's an easy solution for that: Just make the exhaust pipe bigger. Bigger pipe, lower gas velocity, less pressure drop, so less backpressure. Wow, that was easy. After all, this is the way it's done for basically any type of commercial plumbing system. Need less pressure drop on a chilled water pipe or a natural gas line? Just make the pipe bigger.

    But wait, there's a problem....Having a huge exhaust pipe has killed my low end torque!!! What's different? Oh, there's no backpressure!! Therefore backpressure makes torque!

    Wrong.

    An exhaust system is different than just about any other plumbing situation. How? Because the flow is pulsed, and this turns out to be a big deal. Every time a pulse of exhaust gas runs through the pipe, a strange thing happens: it as it passes, it has a little area of vacuum behind it. Just like a NASCAR stocker running around the track, the pulse generates a little bit of a vacuum behind it. In NASCAR, a driver can take advantage of another driver's vacuum by getting right behind him and driving in it. The wind resistance is drastically reduced. This is called drafting.

    Well, how big the vacuum behind each pules is depends on the gas velocity. The higher the velocity, the bigger the vacuum the pulse has behind it.

    Now, this means that I can "draft" the next pulse, just like in NASCAR. In NASCAR, it's called drafting, in an exhaust system, it's called scavenging. You've probably seen this term used when talking about headers, but the same concept applies in the pipe.

    I get the maximum scavenging effect if the gas velocity is high, so the pipe needs to be small. By maximizing the scavenging effect, I help to pull pulses out of the combustion chamber, which means the engine doesn't have to work as hard to do that.

    This has the most effect when there's a bunch of time between pulses...in other words, at low rpm. As the revs rise, the pulsed flow becomes more and more like constant flow, and the scavenging effect is diminished.

    So, at low rpm I need a small pipe to maximize scavenging, and at high rpm I need a big pipe to minimize pressure drop. My exhaust pipe can only be one size, so it's a compromise. For a given engine, one pipe diameter will make the most overall power (i.e., have the largest area under the curve on a dyno chart).

    So, the loss of torque has nothing to do with backpressure, and everything to do with gas velocity. So you need exhaust components that are not restricive (manifolds/headers, mufflers) and that are sized correctly for your application.

    To further dispel the "backpressure is necessary" theory, try this if you want. If you have access to a vehicle with open headers, make a block off plate that will bolt to the collector. This plate should have only a 1" hole in it for the exhaust to flow through. That will give you PLENTY of backpressure, and zero scavenging. Then you can report back on how much low end power it has.

    The one exception to sizing an exhaust is for turbo cars. Since the turbo is in the exaust stream, the gas flow spinning the impeller tends to come out of the turbo with the pulses greatly diminished. In this case, you can get away with running a larger pipe than on an equivalent HP N/A engine because you can't take as much advantage of the scavenging effect.

  14. #74
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    let me make this clear tho..i have ALOT of respect for you N20LT4..i dont have really any hands on experience like you..so i am not calling you a lier or anything like that just trying to share some of the knowledge i have read about with people and even you.

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    Quote Originally Posted by shady milkman View Post
    let me make this clear tho..i have ALOT of respect for you N20LT4..i dont have really any hands on experience like you..so i am not calling you a lier or anything like that just trying to share some of the knowledge i have read about with people and even you.
    That is a great write up! You know, the whole back pressure issue has always been a debate. I've always believed in it, but there has never been any solid proof - or any real way to prove that it does contribute to low-speed torque. Nonetheless, that right up speaks on several key points that forces me look at the issue in a different light. Thanks for sharing that!

  16. #76
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    Quote Originally Posted by N20LT4 View Post
    That is a great write up! You know, the whole back pressure issue has always been a debate. I've always believed in it, but there has never been any solid proof - or any real way to prove that it does contribute to low-speed torque. Nonetheless, that right up speaks on several key points that forces me look at the issue in a different light. Thanks for sharing that!
    anytime man.

  17. #77
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    soooooo? was i right?

  18. #78
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    no on the backpressure ..but yes on sound.

  19. #79
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    ok.

  20. #80
    member since may 2000 nhraformula's Avatar
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    Quote Originally Posted by N20LT4 View Post
    Whomever told you backpressure was a myth...lied to you! Different exhaust setups undoubtedly will alter low-speed grunt.
    why is it that all drag cars run open headers if its a myth?
    any amount of low end tq you may lose will quickly be made up.

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