Will a cat delete and true 3" exhaust to stock mufflers flow close to headers +
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2009-2014 Cadillac CTS-V Performance Mods Discussion, Will a cat delete and true 3" exhaust to stock mufflers flow close to headers + in Cadillac CTS-V Series Forum - 2009-2014; I heard from a local shop that a stock exhaust manifold flow really well like shorty headers from the factory. ...
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    Moparman4444 is offline Cadillac Owners Enthusiast
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    Will a cat delete and true 3" exhaust to stock mufflers flow close to headers +

    I heard from a local shop that a stock exhaust manifold flow really well like shorty headers from the factory. The question is:

    Will stock exhaust manifold plus a cat eliminator and a true 3" exhaust back to stock mufflers will flow almost as well as long tube headers and a catback system for a car putting out 630 to the wheels?

    Has anyone ever done any comparative testing to show the differance?

    I know longtube headers and an open exhaust will flow better at high RPM's but for low to mid range RPM and general street driving, is ther really a differance warranting the cost?

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    Moparman4444 is offline Cadillac Owners Enthusiast
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    Re: Will a cat delete and true 3" exhaust to stock mufflers flow close to headers +

    I need to add one more thing, my 2009 V ran low 11's on slick, hockey puck like PS2 street tires. It was an easy 10 second car with sticks.
    The car had stock manifolds, factory cats and mufflers But had a mandrel bent center section between the cats and the mufflers which came from Jesse at WAIT4ME. Exhaust flowed really nicely and was only about 5% louder than stock IMHO. This is what Im using for comparison to headers and full exhaust.

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    Da V-Man is offline Cadillac Owners Fanatic
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    Re: Will a cat delete and true 3" exhaust to stock mufflers flow close to headers +

    There's no benefit to 3" pipes if you're still pushing the exhaust gasses through 2½" mufflers. All you'll do is make it louder.

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    thebigjimsho is offline Cadillac Owners 10000+ Posts
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    Stock manifolds do flow well. But I still dropped my boost with headers, which, along with the added sound, was my goal...

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    Moparman4444 is offline Cadillac Owners Enthusiast
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    Re: Will a cat delete and true 3" exhaust to stock mufflers flow close to headers +

    DaV Man was right. I measured the pipes going into my rear mufler on my coupe and they are 2 1/2" OD pipes. I thought they were 2 3/4" I guess I was wrong.

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    Re: Will a cat delete and true 3" exhaust to stock mufflers flow close to headers +

    Stock manifolds are pretty good to a certain point.

    I've ran 10.87 @ 127 with the stock exhaust.

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    Re: Will a cat delete and true 3" exhaust to stock mufflers flow close to headers +

    Quote Originally Posted by Da V-Man View Post
    There's no benefit to 3" pipes if you're still pushing the exhaust gasses through 2½" mufflers. All you'll do is make it louder.
    This is wrong. Back pressure is a function of the volume of the flow of gasses, the diameter of the pipe and the length of piping at that diameter.

    10' of 3" pipe with 1' of 2.5" pipe connected together will have less back pressure than 10' of 2.5" pipe with 1' of 3" connected together for the same volume of gas passing through both scenarios.

    When you step down from 3" to 2.5" the exit velocity will increase, simple said the gasses will be flowing out the end of the pipe at a faster speed.

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    Re: Will a cat delete and true 3" exhaust to stock mufflers flow close to headers +

    There are guys who have used stock LS1 manifolds (worse design) and gone 8s in the quarter mile on a turbo setup. Personally I think the V stock manifolds are a work of art and the dollar difference isn't worth:

    1 - the hassle
    2 - the price.

    Just my opinion but I think you're plan is fine and will easily support huge power.

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    Da V-Man is offline Cadillac Owners Fanatic
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    Re: Will a cat delete and true 3" exhaust to stock mufflers flow close to headers +

    Quote Originally Posted by wetcoast View Post
    This is wrong. Back pressure is a function of the volume of the flow of gasses, the diameter of the pipe and the length of piping at that diameter.

    10' of 3" pipe with 1' of 2.5" pipe connected together will have less back pressure than 10' of 2.5" pipe with 1' of 3" connected together for the same volume of gas passing through both scenarios.

    When you step down from 3" to 2.5" the exit velocity will increase, simple said the gasses will be flowing out the end of the pipe at a faster speed.
    The 2½" pipe you're referring to is not a pipe, per se - it's a factory muffler. That means it's a designed restriction. Unlike straight-through aftermarket performance mufflers, it has baffles and other structures to redirect gas flow internally, which causes sound waves to bounce around inside the casing, dissipating their energy. It does not necessarily obey the laws of fluid dynamics. The only way to increase flow through it is to increase the pressure differential across it. That means a larger amount of back pressure.

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    Re: Will a cat delete and true 3" exhaust to stock mufflers flow close to headers +

    Quote Originally Posted by Da V-Man View Post
    The 2½" pipe you're referring to is not a pipe, per se - it's a factory muffler. That means it's a designed restriction. Unlike straight-through aftermarket performance mufflers, it has baffles and other structures to redirect gas flow internally, which causes sound waves to bounce around inside the casing, dissipating their energy. It does not necessarily obey the laws of fluid dynamics. The only way to increase flow through it is to increase the pressure differential across it. That means a larger amount of back pressure.
    Pipe or muffler it will have a definite pressure loss for the volume of gas passing through it. Pressure losses in an exhaust system are cumulative. If you decrease the pipe pressure loss between the exhaust port on the cylinder head and the muffler it will reduce the overall back pressure. Albeit, the pressure loss in the muffler is likely a lot larger than the pressure loss in the pipe leading up to it rendering the improvement from changing 2.5" pipe to 3" negligible.

    I do this for a living applying combustion engines in back up power generation systems into buildings where we have to design exhaust systems into different building configurations everyday.

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    Moparman4444 is offline Cadillac Owners Enthusiast
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    Re: Will a cat delete and true 3" exhaust to stock mufflers flow close to headers +

    Not being an engineer who has a working understanding of fluid dynamics, I was under the imprssion that if you have a factory muffler and add headers, then your flow would not increase because the muffler is more restrictive than the headers and would still cause a backup in the system. IE you need a system that all works together and complements the other components.

    So what Wetcoast is saying is, the addition of a 3" center piping will help if I were to also install better mufflers. I think?

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    Da V-Man is offline Cadillac Owners Fanatic
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    Re: Will a cat delete and true 3" exhaust to stock mufflers flow close to headers +

    Simply stated, compared to the pipe feeding it, the muffler is the restriction that limits flow. Putting a bigger pipe in front of the muffer does not lessen its impact as a restriction. From a street-driven perspective, I would use a better flowing muffler and forego the bigger pipe.

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    Re: Will a cat delete and true 3" exhaust to stock mufflers flow close to headers +

    I think it depends on your power goals. If you are looking for more than 800RWHP then it might be worth it to you. I personally think you can support 800RWHP through the stock manifolds and catless mid pipe without too much trouble. Even into stock mufflers.

    Depends on if the ~2K in cost is worth it to you.

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    Re: Will a cat delete and true 3" exhaust to stock mufflers flow close to headers +

    Quote Originally Posted by Moparman4444 View Post
    Not being an engineer who has a working understanding of fluid dynamics, I was under the imprssion that if you have a factory muffler and add headers, then your flow would not increase because the muffler is more restrictive than the headers and would still cause a backup in the system. IE you need a system that all works together and complements the other components.

    So what Wetcoast is saying is, the addition of a 3" center piping will help if I were to also install better mufflers. I think?
    Just saying that the larger pipe will decrease the total back pressure. It may be so small of a difference that it doesn't make any power difference.

  16. #15
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    Re: Will a cat delete and true 3" exhaust to stock mufflers flow close to headers +

    Best setup you can do is Long tune 1 7/8 with 3" midsecion squeezin down to stock mufflers. YOu will retain stock torque curve but gain on the top.

    The exhaust gas is hot when if comes out of the heads, there for needs more space to move around, as it cools you wanna squeeze it to accelerate it. thus the need to reduce from a 3"-2.5"

    3" is all noise and only top end power, you sacrifice bottom end torque, mind you a SC likes a little back pressure, it helps the sc reach boost quicker than if you run a catless 3" system

    I have seen it on all the sc cars in my area. They do a dyno run then remove the cats and suddenly they lose 10-20hp.

    ----------

    Best setup you can do is Long tune 1 7/8 with 3" midsecion squeezin down to stock mufflers. YOu will retain stock torque curve but gain on the top.

    The exhaust gas is hot when if comes out of the heads, there for needs more space to move around, as it cools you wanna squeeze it to accelerate it. thus the need to reduce from a 3"-2.5"

    3" is all noise and only top end power, you sacrifice bottom end torque, mind you a SC likes a little back pressure, it helps the sc reach boost quicker than if you run a catless 3" system

    I have seen it on all the sc cars in my area. They do a dyno run then remove the cats and suddenly they lose 10-20hp.

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