The theory of getting long tube headers. - Mustang Evolution

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Old 10-07-2014, 06:54 PM   #1
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The theory of getting long tube headers.

When we put on long tube headers using the same straight pipe after the x pipe ( catted or not ) and same mufflers how are we getting gains? I understand that the new long tube headers are less restricting then stock headers but why does that even matter when you are channeling that exhaust into the same stock straight pipe ? Shouldn't you increase the diameter in your straight pipes and mufflers to really get any gains ?

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Old 10-07-2014, 08:18 PM   #2
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It's all about the velocity of the gasses going through the tube. Trying to put it in the most layman terms I can think of. The smaller and longer the tube the faster air will travel through it.

Fluid dynamics concepts.


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Old 10-07-2014, 09:49 PM   #3
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I thought it had to do with giving each cylinder a little more "breathing room" so the exhaust gasses aren't hitting each other as much. You do also want to increase the overall diameter and flow all the way down also if possible.

Its like they (exhaust gases coming from each cylinder) are waiting in line for the next guy to move out the way. Long tubes give them longer lines to hold/expand the queued gases with out getting backed up. If that makes sense.
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Old 10-07-2014, 11:09 PM   #4
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Yeah I hear what u guys are saying but For sake of argument don't those same gasses get forced together before the x pipe regardless of the how long the headers are . So I guess I mean to say is since it's the same diameter of piping shouldn't any given square inch of exhaust leave the tail pipe at the same rate regardless of the headers ?

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Old 10-07-2014, 11:11 PM   #5
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Stock header compare to BBK long tube.
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Old 10-07-2014, 11:34 PM   #6
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The theory of getting long tube headers.

Quote:
Originally Posted by c_rizzle View Post
I thought it had to do with giving each cylinder a little more "breathing room" so the exhaust gasses aren't hitting each other as much. You do also want to increase the overall diameter and flow all the way down also if possible.

Its like they (exhaust gases coming from each cylinder) are waiting in line for the next guy to move out the way. Long tubes give them longer lines to hold/expand the queued gases with out getting backed up. If that makes sense.

Keep in mind that regardless of whether you have shorties or long tubes, the gasses are all traveling the same distance from cylinder head to muffler. The long tube headers require a modified midpipe to accommodate their length. So they both have the same "breathing room".


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Originally Posted by geepoons View Post
Yeah I hear what u guys are saying but For sake of argument don't those same gasses get forced together before the x pipe regardless of the how long the headers are . So I guess I mean to say is since it's the same diameter of piping shouldn't any given square inch of exhaust leave the tail pipe at the same rate regardless of the headers ?

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It's fluid dynamics. A physics principal that is a lot more than I could explain in a forum post. The long tube headers will increase the velocity, therefore leaving at a higher rate.

There's a balance between the diameter and length of the tubes. If the diameter is too large it will make the exhaust gas expand and cause them to slow down.

I understand thinking it's about volume, but it's really about velocity.






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Old 10-08-2014, 12:08 AM   #7
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I seem to have a better understanding thanks guys

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Old 10-08-2014, 08:46 AM   #8
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Velocity, turbulance/vector of gases & volume of pipe(s) all affect how well an exhaust system works.

Lets say you have 3 long tubes at 1.5" diameter that merge to a 3" pipe. (i'm not sure about the sizes of this particular set up, but the same math generally applies... more pipes = more volume.)

(diameter x pi x # of pipes)

That 3" pipe is a bottleneck at (3 x 3.14 x 1 ) = 9.42 square inches of space

The three 1.5" pipes have a combined size of ( 1.5" x 3.14 x 3 ) = 14.13 sq inches

So longer headers give them 50% more room to expand from the engine and get moving in the right direction..... AND then the part you're talking about with velocity... having a longer pipe decreases turbulence, so the air is heading the correct direction by the end of the long header... so they mix easier at the better joint, so better air flow.

Also some stock headers like the one pictured aren't optimal, b/c the headers aren't of equal length. Usually you want the section of pipe from the block to the merge point as equal as possible, which is why you often see the cylinder closest to the rear of the car (shortest distance to go) have extra bends in it to make the distances all the same.
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Old 10-08-2014, 08:46 AM   #9
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Whew... here we go, from the top.

"Tuned length headers" make power because of the way they effect the exhaust gasses. When the cylinder fires, and the exhaust gas starts making its way down the LT runner, it creates a high pressure zone.
When that high pressure zone reaches the collector the other 2 runners are "low pressure zones" in comparison, and the high pressure wave will actually reverse direction back up 1 of the runners (depending on firing order). Once that pressure wave reaches the exhaust valve it will reverse direction again, and if this is timed properly, will be moving away as that exhaust valve is opening and actively put a vacuum on the cylinder which helps pull the exhaust gas out. The reason NA motors like overlap is because when the exhaust is putting a vacuum on the cylinder, if the intake valve is open as well, it pulls more fresh air into the cylinder than it otherwise could on its own. You can see how this is virtually impossible on the stock Log style manifold, as all the gas is basically just being pushed out.

As far as going into the catback. When the pulses are separated like this, and not just all crammed at once, they take up significantly less space in the exhaust pipe.

In regards to velocity, that's where things start getting tricky. In the old days, you always used to hear: "bigger exhaust gives horsepower but loses torque," which is 100% true. Torque is determined by velocity; namely, how fast air enters and leaves the cylinder. A skinny pipe will have a high velocity, and great torque, at the cost of horsepower higher up due to physical flow restrictions. Consequently, a larger pipe would reduce torque for the sake of better flow at the top end.
With the advances in these Ti-Vct motors however, we can manipulate the cam events to match our exhaust set up, and see massive gains in both torque and horsepower by tuning the exhaust gas pulses to be more efficient. Keep in mind also, removing the cats will improve velocity.

Lastly, 2.25" piping is not as small as you think. A single 2.5" catback on a turbo 4 cylinder will support 400 whp, and you have TWO 2.25" pipes trying to support ~300 whp. It is more than enough pipe. Hell, the Terminators use dual 2.5" pipes.
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Old 10-08-2014, 08:56 AM   #10
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With all the fart smellers.. I mean smart fellas in here, we should get our CAD & fluid dynamic computer model simulators out and design a better exhaust system than Ford or any of the after market guys.

Personally, with the money I'm spending on my car with aftermarket parts already (almost $5k) and much more planned in future, I'm kinda wishing I had just ponied up the extra for a Shelby GT500 Convertible. I wasn't THAT far off, with having a loaded GT Premium Convertible at $46k.

Then I'd have all the better parts that I'm going to end up putting on anyway and have them with a warranty... and the big one.... I'd have better resale value.
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Old 10-08-2014, 09:55 AM   #11
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The theory of getting long tube headers.

This is exhausting.
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Old 10-08-2014, 10:04 AM   #12
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Quote:
Originally Posted by VIG View Post
This is exhausting.
People saying exhaust threads are exhausting is exhausting to hear. Even though they are right, it is exhausting to hear about exhaust repeatedly. We've exhausted the exhaust topics.
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Old 10-08-2014, 10:06 AM   #13
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I need a nap.
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Old 10-08-2014, 10:07 AM   #14
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Quote:
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I need a nap.
You exhausted of hearing about the exhaustive exhaust topics?
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Old 10-08-2014, 10:28 AM   #15
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I'm the residual byproducts of hydrocarbon combustion of this conversation .... am i doing it right?
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Old 10-08-2014, 12:23 PM   #16
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This is good stuff

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Old 10-10-2014, 11:21 AM   #17
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What do y'all think about the super beast system by pypes from American muscle. (Long tubes, off road x, and the pype bombs.) is it worth the money to run them on my 4.6 3v??


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Old 10-10-2014, 11:36 AM   #18
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with pipe size also consider water flowing through a garden hose vs the same volume of water flowing through a sewer pipe; which travels faster? the restriction actually makes it move faster out of the system
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Old 10-11-2014, 01:38 PM   #19
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with pipe size also consider water flowing through a garden hose vs the same volume of water flowing through a sewer pipe; which travels faster? the restriction actually makes it move faster out of the system
Bad analogy. A hose generally has a much higher pressure usually from a large elevated reservoir.
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