Shorty Headers Versus Longtube Headers

[BlueOvalBlood]

I have the MACs with a MAC offroad X...I can def feel a differenc and I am naturally aspirated. See my thread on this whole topic, it has a lot of factual numbers and all diff setups guys on here are running. LTs are gonna be more and more powerful the more you modify your car. Meaning, you will get all of your mods capabilities with the better flowing LTs. PLus, they make your car sound PISSED! lol, I have had non stop compliments since I had them installed. Shorties will give you gains as well, just if you plan on adding more things, you will get the best results with LTs. If you want to go to my youtube and hear for yourself, i can leave the links once again. I need to go make some new ones now that they LTs have broken in a lil more

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[SirKnightTG]

Wow this thread was old. 2006!

[Nichoms]

I did a final project on exhaust scavenging in my thermal fluids lab so I had to do a lot of research on scavenging. I'm not saying I know everything about it at all but I will expand on what was mentioned earlier about scavenging:

Well first, there are two kinds of scavenging; Wave scavenging and Inertial scavenging. I will briefly explain what both of them are.
Wave scavenging is caused by the energy wave exiting your exhaust chamber when your exhaust valve opens. The rapidly expanding gases exiting your exhaust chamber cause a very fast energy wave (~1500 ft/sec) to go pass through your exhaust pipe (starting through your manifold). This wave has negligible mass and is pretty much just energy. When this wave hit the first low pressure zone it finds (could be a step up in size of your primaries, your manifold collector, and prochamber, your muffler, or just when it exits to atmosphere) it sends back a reversion wave in the opposite direction. This reversion wave that gets sent back is moving at pretty much equal velocity (~1500 ft/sec) as the energy wave that caused it. This wave has two nodes to it. The front of the wave (Compression node) is at high pressure, and the back of the wave (Rarefaction node) is at low pressure. This next part is what matters most in inertial scavenging... When the reversion wave reaches the exhaust valve one of three things can happen, which one of these three things depends on the location of the first low pressure zone that causes the reversion wave. 1. The reversion wave hits the exhaust valve when it is closed and bounces back and out of the exhaust pipe (no scavenging effect) 2. The high pressure (Compression node) hits the exhaust valve when it opens and pushes exhaust back into the chamber (losing power by making you force that exhaust back out) and 3. The compression node hits the closed exhaust valve and bounces back, then it opens while the low pressure (Rarefaction node) is next to it and the low pressure sucks the exhaust out of the chamber (Wave Scavenging effect)
So the key is to get the perfect length pipe, so that the Reversion wave's rarefaction node is next to the exhaust valve when it opens. Some custom tuned formula headers can pull as much as -6 psi, sucking all the exhaust out of the chamber, and with valve overlap, sucking new fresh air/fuel into the chamber. This is why scavenging has such a great effect on NA cars, because it is literally sucking in the intake charge.

The second type of scavenging is more basic:
Inertial scavenging is just caused by the mass of exhaust gas moving through the manifold. As you know each piston isn't firing at all times, so there are pulses making gaps in the exhaust flow. These masses of moving gas have inertia and they pull the surrounding exhaust gasses with it. Since the exhaust valve closes behind it this moving mass of gas causes a vacuum (low pressure) behind it. This vacuum, depending on where it is in the manifold, either sucks the exhaust out and intake into the chamber the next time the exhaust valve opens, or it pulls the gas behind it so it all moves quicker.

So pretty much any header you get will have better inertial scavenging than your stock manifolds but to get properly tuned pipe length for your particular engine to achieve perfect Wave scavenging it is a lot harder. No header you will buy can get perfect wave scavenging, the only way to get that is with custom hand-made headers, that have been tuned on a dyno for your exact engine. Pretty much only if you have a racing team with a large budget.
And also if the tubes are all the same length but they are the wrong length then every one of your cylinders is getting incorrect scavenging. But after all that I would still go with longtubes because they make more power on dynos', so obviously they are closer to the correct length than the shorties.

I know that is a crapload to read but I thought some of you might enjoy the information

sorry if there are any mispellings or anything, it was too long to proof-read haha

[East87]

Originally Posted by Nichoms

I did a final project on exhaust scavenging in my thermal fluids lab so I had to do a lot of research on scavenging. I'm not saying I know everything about it at all but I will expand on what was mentioned earlier about scavenging:

Well first, there are two kinds of scavenging; Wave scavenging and Inertial scavenging. I will briefly explain what both of them are.
Wave scavenging is caused by the energy wave exiting your exhaust chamber when your exhaust valve opens. The rapidly expanding gases exiting your exhaust chamber cause a very fast energy wave (~1500 ft/sec) to go pass through your exhaust pipe (starting through your manifold). This wave has negligible mass and is pretty much just energy. When this wave hit the first low pressure zone it finds (could be a step up in size of your primaries, your manifold collector, and prochamber, your muffler, or just when it exits to atmosphere) it sends back a reversion wave in the opposite direction. This reversion wave that gets sent back is moving at pretty much equal velocity (~1500 ft/sec) as the energy wave that caused it. This wave has two nodes to it. The front of the wave (Compression node) is at high pressure, and the back of the wave (Rarefaction node) is at low pressure. This next part is what matters most in inertial scavenging... When the reversion wave reaches the exhaust valve one of three things can happen, which one of these three things depends on the location of the first low pressure zone that causes the reversion wave. 1. The reversion wave hits the exhaust valve when it is closed and bounces back and out of the exhaust pipe (no scavenging effect) 2. The high pressure (Compression node) hits the exhaust valve when it opens and pushes exhaust back into the chamber (losing power by making you force that exhaust back out) and 3. The compression node hits the closed exhaust valve and bounces back, then it opens while the low pressure (Rarefaction node) is next to it and the low pressure sucks the exhaust out of the chamber (Wave Scavenging effect)
So the key is to get the perfect length pipe, so that the Reversion wave's rarefaction node is next to the exhaust valve when it opens. Some custom tuned formula headers can pull as much as -6 psi, sucking all the exhaust out of the chamber, and with valve overlap, sucking new fresh air/fuel into the chamber. This is why scavenging has such a great effect on NA cars, because it is literally sucking in the intake charge.

The second type of scavenging is more basic:
Inertial scavenging is just caused by the mass of exhaust gas moving through the manifold. As you know each piston isn't firing at all times, so there are pulses making gaps in the exhaust flow. These masses of moving gas have inertia and they pull the surrounding exhaust gasses with it. Since the exhaust valve closes behind it this moving mass of gas causes a vacuum (low pressure) behind it. This vacuum, depending on where it is in the manifold, either sucks the exhaust out and intake into the chamber the next time the exhaust valve opens, or it pulls the gas behind it so it all moves quicker.

So pretty much any header you get will have better inertial scavenging than your stock manifolds but to get properly tuned pipe length for your particular engine to achieve perfect Wave scavenging it is a lot harder. No header you will buy can get perfect wave scavenging, the only way to get that is with custom hand-made headers, that have been tuned on a dyno for your exact engine. Pretty much only if you have a racing team with a large budget.
And also if the tubes are all the same length but they are the wrong length then every one of your cylinders is getting incorrect scavenging. But after all that I would still go with longtubes because they make more power on dynos', so obviously they are closer to the correct length than the shorties.

I know that is a crapload to read but I thought some of you might enjoy the information

sorry if there are any mispellings or anything, it was too long to proof-read haha

That was incredibly informative and well-composed. Thanks.

[loots06]

I have JBA shorty headers and I'm pretty happy with them. I also have a whipple SC HO kit on my car too, its alright.