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Old 12-22-2009, 03:25 PM   #1
OLD MANS 04-RS
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Default Any Benefit To Catless Without Engine Management?

Simple question, if someone only replaces the cat with a trackpipe, will you help or hurt performance without engine management. This on a N/A .
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Old 12-22-2009, 03:33 PM   #2
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It won't make much of a difference either way. Headers will make your biggest difference in the exhaust, everything else stock at least.
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Old 12-22-2009, 03:38 PM   #3
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I have heard headers do nothing more on our cars than make them sound nice.
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Old 12-22-2009, 03:45 PM   #4
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That's if you get unequal length. If you get equal length headers, you will get a bit of an increase in power over pretty much the entire powerband.
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Old 12-22-2009, 03:46 PM   #5
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Quote:
Originally Posted by OLD MANS 04-RS View Post
I have heard headers do nothing more on our cars than make them sound nice.
This isn't true. I got 12whp on the dyno with headers. I got 1 more whp with a track pipe. It was noisy as hell. I took it off the next day and reinstalled my high flow cat.
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Old 12-22-2009, 03:50 PM   #6
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What kind of headers? Is this the Matt Monson who used to live in Harvard Illinois?
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Old 12-22-2009, 04:00 PM   #7
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Anyone on this? Most I have ever seen is 3-4 HP with headers.
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Old 12-22-2009, 04:10 PM   #8
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At BOXER4RACING, they are saying dynos show a consistant 10-12 hp with a trackpipe.
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Old 12-22-2009, 06:31 PM   #9
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what year N/A? the header being replaced will make a difference since they changed to a better, EL-like design in 06.

an old high mileage cat with lots of build up and small ID on the inlet and outlet would most certainly benefit somewhat, but a newer design, like the 06+ cats that are integrated into the exhaust manifold cant be replaced without doing headers or some custom stuff, and gains will be small anyway.
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Old 01-29-2010, 04:50 AM   #10
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I was thinking about doing a full exhaust on my '02 TS with a track pipe. Also wondering about any performance gains. Does anybody have a sound clip with a track pipe?
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Old 01-29-2010, 01:08 PM   #11
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wrong thread...

Last edited by RaceCarRiot; 02-15-2010 at 07:28 PM.
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Old 02-13-2010, 01:28 AM   #12
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your a loser for polluting our air with your catless set up. get a high quality high flow cat bro.
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Old 02-13-2010, 02:09 AM   #13
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u didn't answer his question.
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Old 02-13-2010, 04:54 AM   #14
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correct me if im wrong but on turbo'd cars you will feel a difference going catless, but on n/a cars you need a cat(s) for that needed backpressure.
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Old 02-13-2010, 01:45 PM   #15
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Quote:
Originally Posted by silverbug-i View Post
correct me if im wrong but on turbo'd cars you will feel a difference going catless, but on n/a cars you need a cat(s) for that needed backpressure.
Oh for Frack's sake...

NA CARS DO NOT NEED BACKPRESSURE! BACKPRESSURE IS ALWAYS A BAD THING!
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Old 02-13-2010, 02:19 PM   #16
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Originally Posted by williaty View Post
Oh for Frack's sake...

NA CARS DO NOT NEED BACKPRESSURE! BACKPRESSURE IS ALWAYS A BAD THING!
so your 5 inch exhaust makes your n/a car run like a top
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Old 02-13-2010, 02:59 PM   #17
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No, because the 5" exhaust would allow the exhaust velocity to drop. Backpressure is nothing but parasitic loss. Exhaust gas velocity is everything.

It amazes me that there are still people too stupid to have learned that.
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Old 02-13-2010, 04:02 PM   #18
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Quote:
Originally Posted by williaty View Post
Oh for Frack's sake...

NA CARS DO NOT NEED BACKPRESSURE! BACKPRESSURE IS ALWAYS A BAD THING!

thanks douche for being the cool guy, i wasnt to sure thats why i said "CORRECT ME IF IM WRONG".
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Old 02-13-2010, 04:53 PM   #19
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Quote:
Originally Posted by williaty View Post
No, because the 5" exhaust would allow the exhaust velocity to drop. Backpressure is nothing but parasitic loss. Exhaust gas velocity is everything.

It amazes me that there are still people too stupid to have learned that.
so what you are saying is a 4 stroke engine does not need any back pressure. but wouldnt a smaller exhaust make more exhaust velocity and make more power too
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Old 02-13-2010, 05:19 PM   #20
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Originally Posted by bandit_2017 View Post
so what you are saying is a 4 stroke engine does not need any back pressure. but wouldnt a smaller exhaust make more exhaust velocity and make more power too
Maybe. There's too many variables to make a simple statement like that. Yes, narrower piping should increase exhaust gas velocity. However, it's often hard to increase velocity without something undesirable (like backpressure) coming along for the ride. There's also a point at which the diameter of the piping itself becomes a restriction. Then there's the fact that the engine makes different volumes of exhaust gas at different throttle opening angles and different engine speeds. A tubing diameter that's correct for one engine speed and throttle opening will be incorrect for another. This is where the need to size your exhaust to your desired power band and engine output comes from.

So it's not that simple. The only real rule is that backpressure is always bad bad and correct exhaust gas velocity is always right. It's just that achieving those two goals at the same time gets really complicated.
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Old 02-15-2010, 11:03 AM   #21
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Ahhh.... my favorite automotive urban-myth.... Backpressure!!

http://forums.nasioc.com/forums/show...p?t=1630548#22
http://www.rs25.com/forums/f5/t37483...kpressure.html

My quest to rid the world of this myth continues!!
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Old 02-15-2010, 11:41 AM   #22
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It annoys me every time someone comes up with the backpressure myth, and then defends it by using extremes such as 5" pipe, or super narrow piping.

Backpressure is basically "clogging the pipes"
Try welding a metal plate to the exhaust manifold and then drill a pinhole.
All backpressure, no exhaust scavenging. I don't think you'll get much power.

In a super perfect hyper technologically advanced world, we would all have exhaust systems that would change diameters as the RPMs change.

The optimal diameter for a given engine is dependent on how much exhaust gas/flow is coming out of the engine. At lower RPMs, it is beneficial to have a narrow exhaust because with the low amount of exhaust gases out, a smaller diameter exhaust would be able to provide sufficient flow while being narrow enough to provide an exhaust scavenging effect. To large and this vacuum pulling effect is lost, decreasing flow. Of course, this would quickly change near redline where the higher volume of gases would not be able to pass through this narrow piping quickly enough, thus creating what we called backpressure preventing flow. A larger diameter will then reduce backpressure and restore the exhaust scavenging effect.

We don't have such magical exhausts, so the only thing we can do is have a diameter that will act as a compromise of sorts. Many here are running 2.25" piping past the headers which pretty much allows for the maximum CFM of our engines.
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Old 02-15-2010, 01:36 PM   #23
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To large and this vacuum pulling effect is lost...
Sorry, I never understood that vacuum thing. If you put a pressure gauge on one of the primaries, will you ever measure pressure lower than outside? Lets say if you drive a car that doesn't even have headers installed, granted it would be laud as hell, will it be slower because the lack of this "vacuum?"
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Old 02-15-2010, 01:42 PM   #24
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Yes, you'll measure near perfect vacuums followed by significant overpressures. However, that's not the effect really being discussed here. There's resonant scavenging and velocity scavenging. In resonant scavenging, the length of the pipes matters. The idea is that the near perfect vacuum "echo" of another cylinder firing arrives at the exhaust valve just as the valve opens, giving the cylinder a vacuum to dump into. Velocity scavenging is the idea that, once you get the exhaust gasses moving, they'd rather not stop. So you let the rush out of the cylinder and the momentum of the majority of the gasses keeps them moving as the cylinder empties eventually resulting in a partial vacuum that helps "suck" the last bit of exhaust gasses out of the cylinder. This effect is dependent on getting the correct velocity (both too high and too low are bad) so the diameter of the pipe matters.
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Old 02-15-2010, 01:47 PM   #25
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Quote:
Originally Posted by Jerry Xu View Post
Sorry, I never understood that vacuum thing. If you put a pressure gauge on one of the primaries, will you ever measure pressure lower than outside? Lets say if you drive a car that doesn't even have headers installed, granted it would be laud as hell, will it be slower because the lack of this "vacuum?"
I'm not sure if we could ever truly test your question, but I do believe that at least in the header, the exhaust isn't a continuous flow but a series of "pulses" in which (in my eyes as a student in Animal Science) is kind of like a bolus of food going down an esophagus. Even when you drink water it's not like a drain, but gulps. In between those gulps, the esophagus closes due to the lack of matter. ("vacuum" i feel like it's really more of a misnomer) Except in this case, the header remains open, and the vacuum is generated by the gas pulse rushing through pushing everything out leaving a vacuum. I almost feel like I should say that it's like slipstreaming in F1. This vacuum then assists in what's generally called exhaust scavenging by helping pull in fresh intake charge during the intake-exhaust valve overlap.

This is why EL headers are "better" than UEL since the exhaust pulses will end up combining at the same time and not ruin the vacuum effect.

Is it truly a vacuum? Probably not, I feel like it's a misnomer. However, I do believe that there is a significantly lower pressure in relative to the surrounding portions of the exhaust tract, and more specifically in between the pulses and the cylinder.
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