Equal-length headers?
Thread Starter
|
Lead Driver
Joined: Sep 2002
Posts: 9,182
Likes: 12
From: Gateway to the West
Equal-length headers?
I realize to some this may be common knowledge and you may be thinking, good grief GS92 is expounding again... Arrrghhh! Well for those who already understand this concept go seek out something more fascinating. For those who may be wondering or not realize what it truly means, I figured I'd try a little explanation. Since so many questions are fielded in this forum regarding headers and exhaust systems I thought it might be a good idea to make folks aware of the benefits of choosing a header that has been designed this way.
So, equal-length headers, what makes 'em different from other headers?
Each tube from the exhaust port at the cylinder head down to the collector at the base of the header is the same length. If you could uncurl them and lay them all out side-by-side they would all be the same length.
And just what is the benfit of this... doesn't that make for a lot more bends and curves for the exhaust to travel through and make the header take up more space?
Well, the latter part of the answer is yes, it does make them a touch bulkier but its worth it and there are units available with this design feature that will fit in place of the OEM manifolds without modifications for space.
And yes, it makes for a few more bends in some cases but they are worth it for this reason. They flow better!
How?
By allowing the exhaust leaving the cylinders a place to go without "bottlenecking" at the collector. Imagine for just a minute that you have four sinks (or six if you happen to have a 300 I6 in your truck with this type of header). Each sink is filled and emptied in succession just like the cylinders in an engine. When the drain (exhaust valve) is opened, the water flows down into the pipe and heads for the sewer (main exhaust pipe). Immediately after that the next drain is opened and the water from it does the same and so on down the line. Now imagine that the pipe from the drain to the main sewer from each sink is the exact same length (like an equal length header would be). So the water from the first sink is in the pipe heading for the sewer. The water from the second sink starts into the next pipe but it has to run the same distance as the water from the first did. Not being slowed down really, just has the same distance to cover before it reaches the sewer. Well, that means the water from the first sink will have enough time to get into the sewer BEFORE the water from the second sink does. This way the water from the second sink will not "collide" with the water from the first inside the sewer which will slow down the flow because more water is trying to flow through the same amount of space in the sewer. The additional benfit to this is the vacuum effect created by the water from the first sink behind it in the sewer pipe. This actually helps PULL the water from the second sink down the pipe and into the sewer. And right behind that there is another sink draining into another pipe and pushing the air in front of it down the pipe which gives the water from sink number two a slight PUSH from behind along with the PULL from sink number one. You can begin to see that if each amount of water is the same and released in succession as exhasut would be in an engine, the movement of the water through the pipes will actually help perpetuate the movement, draw the water from the next sink down and push the water from the previous sink out. Its easier to explain and understand when you think of something you can actually see moving like water. The same thing will happen with exhaust gasses and air.
To add to the explanation just a bit further imagine that the pipes from the drains to the sewer are NOT the exact same length but rather whatever length they need to be to reach the sewer. Well the sink closest to the sewer would then be the logical choice to drain first and then the next furthest and the next. But, since we cannot dictate the order in which the sinks are drained and they MUST drain in the order that is predetermined (firing order), the sinks must still be drained in the order that they were with the egual-length setup. But now sink number two is closest to the sewer but sink number one must drain first. So sink 1 drains and the water is flowing towards the sewer. Problem now is that when sink 2 is drained, the water from it will reach the sewer sooner than the water from sink 1. The result, the water from sink 2 runs into the water from sink 1 as they both get to the sewer at nearly the same time. Now more water is trying ot get through the same sewer than before. The vacuum effect does NOT apply, and while the water from sinks 1 and 2 is trying to stuff itself down the sewer, the water from sink three is already on its way adding its own set of flow-hindering problems. This is what happens in most conventional exhaust manifolds. The exhaust gasses from neighboring cylinders run into each other creating turbulence and bottlenecking which slows down the flow into the main exhaust pipe and serves to keep the heat from them nearer the engine which really doesn't need any help staying warm while its running.
So by way of an alternate "plumbing" theory the benefits of opting for a set of equal length headers over manifolds or headers that do NOT feature this design should become fairly obvious.
End of rambling for now.
So, equal-length headers, what makes 'em different from other headers?
Each tube from the exhaust port at the cylinder head down to the collector at the base of the header is the same length. If you could uncurl them and lay them all out side-by-side they would all be the same length.
And just what is the benfit of this... doesn't that make for a lot more bends and curves for the exhaust to travel through and make the header take up more space?
Well, the latter part of the answer is yes, it does make them a touch bulkier but its worth it and there are units available with this design feature that will fit in place of the OEM manifolds without modifications for space.
And yes, it makes for a few more bends in some cases but they are worth it for this reason. They flow better!
How?
By allowing the exhaust leaving the cylinders a place to go without "bottlenecking" at the collector. Imagine for just a minute that you have four sinks (or six if you happen to have a 300 I6 in your truck with this type of header). Each sink is filled and emptied in succession just like the cylinders in an engine. When the drain (exhaust valve) is opened, the water flows down into the pipe and heads for the sewer (main exhaust pipe). Immediately after that the next drain is opened and the water from it does the same and so on down the line. Now imagine that the pipe from the drain to the main sewer from each sink is the exact same length (like an equal length header would be). So the water from the first sink is in the pipe heading for the sewer. The water from the second sink starts into the next pipe but it has to run the same distance as the water from the first did. Not being slowed down really, just has the same distance to cover before it reaches the sewer. Well, that means the water from the first sink will have enough time to get into the sewer BEFORE the water from the second sink does. This way the water from the second sink will not "collide" with the water from the first inside the sewer which will slow down the flow because more water is trying to flow through the same amount of space in the sewer. The additional benfit to this is the vacuum effect created by the water from the first sink behind it in the sewer pipe. This actually helps PULL the water from the second sink down the pipe and into the sewer. And right behind that there is another sink draining into another pipe and pushing the air in front of it down the pipe which gives the water from sink number two a slight PUSH from behind along with the PULL from sink number one. You can begin to see that if each amount of water is the same and released in succession as exhasut would be in an engine, the movement of the water through the pipes will actually help perpetuate the movement, draw the water from the next sink down and push the water from the previous sink out. Its easier to explain and understand when you think of something you can actually see moving like water. The same thing will happen with exhaust gasses and air.
To add to the explanation just a bit further imagine that the pipes from the drains to the sewer are NOT the exact same length but rather whatever length they need to be to reach the sewer. Well the sink closest to the sewer would then be the logical choice to drain first and then the next furthest and the next. But, since we cannot dictate the order in which the sinks are drained and they MUST drain in the order that is predetermined (firing order), the sinks must still be drained in the order that they were with the egual-length setup. But now sink number two is closest to the sewer but sink number one must drain first. So sink 1 drains and the water is flowing towards the sewer. Problem now is that when sink 2 is drained, the water from it will reach the sewer sooner than the water from sink 1. The result, the water from sink 2 runs into the water from sink 1 as they both get to the sewer at nearly the same time. Now more water is trying ot get through the same sewer than before. The vacuum effect does NOT apply, and while the water from sinks 1 and 2 is trying to stuff itself down the sewer, the water from sink three is already on its way adding its own set of flow-hindering problems. This is what happens in most conventional exhaust manifolds. The exhaust gasses from neighboring cylinders run into each other creating turbulence and bottlenecking which slows down the flow into the main exhaust pipe and serves to keep the heat from them nearer the engine which really doesn't need any help staying warm while its running.
So by way of an alternate "plumbing" theory the benefits of opting for a set of equal length headers over manifolds or headers that do NOT feature this design should become fairly obvious.
End of rambling for now.
Last edited by greystreak92; Nov 30, 2005 at 01:26 AM.
