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Backpressure: The MYTH and Why It's Wrong

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Old 03-25-2010, 08:23 PM
  #31  
gtracing
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i get it now....your vehicle is actually propelled forward by the flow velocity/thrust of the exhaust....so if i point my exhausts down, will my rear end lift up?

haha jk
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Old 03-25-2010, 08:23 PM
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MaxToTheG37
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nice post... you would be suprised at how many basic mechanics I have ran into that misuse "backpressure"
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Old 03-25-2010, 11:42 PM
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that was really eye opening. thanks!
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Old 03-25-2010, 11:57 PM
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nice post.
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Old 03-26-2010, 02:35 AM
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ahh, gotcha. Totally agree, for a manifold it's definitely different on a turbo, bigger is not better there.

Originally Posted by Mike
for an exhaust, yes. manifold, not necessarily.
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Old 08-08-2010, 04:59 PM
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Gazan37
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Great find mike. Its amazing how much you can learn in the 5-10 minutes it took to read that
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Old 08-21-2010, 08:24 AM
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dc44
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Hello Mike,

Good information on this post, and by coincidence good choice of video clips. In the first clip (of the 08 vette) at around 00:11 to 00:13 when the car decelerates, what causes the cracking/popping?

I was about to head over to corvetteforum.com to ask, but saw this here so figure I'd ask you as well.

Thanks in advance.

DC

Originally Posted by Mike
I'm not sure what the difference between X and Y pipes are for net gains, but I do know that properly engineered H-pipes will have the same performance gain as a X pipe. The key is that the exhaust pulse overlap on the H-pipe has to be the same as an X pipe for the performance gain to be the same. The difference is the sound; X-pipes give a higher pitched sound, while H-pipes give a lower sound. (Think regular Vette with a catback and stock H-pipe [which btw is crap], and a Vette with a X-pipe and catback)

Z06 with Exhaust

YouTube - 2008 Corvette Z06 with Corsa Exhaust and CAI - Auto Addiction ltd

Z06 with Exhaust and X-pipe

YouTube - 2008 Corvette Z06 With Corsa Mufflers and X Pipe By Serious Autosport


Note how the first clip has that typical "beefy american muscle" sound, while the second one doesn't.
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Old 08-21-2010, 12:47 PM
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cvt
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Originally Posted by Modme
If you expect all comments to be "oh mike you're so great", and bark at anyone that challenges your ideas, then I think it's time to grow up.
I lol'd at this...the jury is still out on mike if he's a brilliant mad scientist or a kid with wicked google skillz...lol
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Old 08-21-2010, 01:06 PM
  #39  
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Originally Posted by dc44
Hello Mike,

Good information on this post, and by coincidence good choice of video clips. In the first clip (of the 08 vette) at around 00:11 to 00:13 when the car decelerates, what causes the cracking/popping?

I was about to head over to corvetteforum.com to ask, but saw this here so figure I'd ask you as well.

Thanks in advance.

DC
It's usually unburnt gas combusting somewhere in the exhaust. You may let off the gas pedal, but if the injector cycle is already started, it will still finish, causing the engine to run rich, and that extra gas is pushed out with the exhaust. Once the exhaust is hot enough, it'll ignite as its coming out. (Usually the cat takes care of this, but with HFCs or a test pipe, the popping is much more noticeable).

I don't have any firsthand experience with V8's.
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Old 08-21-2010, 06:13 PM
  #40  
Ivoidwarranties
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Originally Posted by Mike
It's usually unburnt gas combusting somewhere in the exhaust. You may let off the gas pedal, but if the injector cycle is already started, it will still finish, causing the engine to run rich, and that extra gas is pushed out with the exhaust. Once the exhaust is hot enough, it'll ignite as its coming out. (Usually the cat takes care of this, but with HFCs or a test pipe, the popping is much more noticeable).

I don't have any firsthand experience with V8's.
That's part of it. Another part of it is the immediate effects from staying in gear and getting off the throttle. Google "engine braking".
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Old 08-21-2010, 08:33 PM
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This post explains what I want to tell a lot of people on the forums, but you have to overlook ignorance on here or you'll drive yourself insane trying to set the story straight all the time. Article is spot on, but it didnt mention anything about the two different pulses. The first and by far fastest traveling pulse is the energy pulse that exits when the valve opens. This is where muffler, cat, and x,y,or h pipe placement is crucial. This wave travels much much faster than the spent gases and will reflect (hence its name reflective wave) or resonant many times, thus timing its frequency helps scavenge the gases. The second pulse is the obvious gas pulse. Good write up and I don't know why its referred to as back pressure either. Its just a pressure differential between the cylinder and ambient pressure. When referring to a valve or anything involving different pressures "back pressure" is never used, only pressure differential.
Last edited by G_Thang; 08-21-2010 at 11:50 PM.
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Old 10-09-2011, 07:17 PM
  #42  
kaoticdemize
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I know this is an old thread but had a question about this. Would there be any benefit (on an N/A car) to go cat back to straight pipe?
(no resonators, no mufflers)
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Old 10-09-2011, 08:09 PM
  #43  
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My old truck was a cat to just pipe, it ended halfway too. I lost a ton of power
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Old 10-10-2011, 12:50 AM
  #44  
Mike
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Originally Posted by kaoticdemize
I know this is an old thread but had a question about this. Would there be any benefit (on an N/A car) to go cat back to straight pipe?
(no resonators, no mufflers)
Only with a tune.
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Old 10-10-2011, 06:06 PM
  #45  
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nice thread
hard to find technical stuff like this around
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