one length of pipe will create more back pressure the longer you make it, as it's got more of a load of gas building up.. Staging a header lets the gas start expanding out to the sides, so it doesn't create such a large wall at length.... It softens the blow, while keeping the gasses IN the pipe, to have SOME back pressure...
Lets it dump the exhaust faster, without just running an open block... It'll be able to snap to life faster, yet have enough back pressure to run good.. Kinda like an expansion chamber on a 2 stroke..
Lets it dump the exhaust faster, without just running an open block... It'll be able to snap to life faster, yet have enough back pressure to run good.. Kinda like an expansion chamber on a 2 stroke..
Quote" Step-Header Designs
Many of you who are reading this article may never have heard of a step-header. This is because step-headers are used almost exclusively in race-only applications. A step-header design is that which has more than one size (diameter) of primary tubing. You start with a smaller header tube diameter at the cylinder head, and then have one or two larger sizes which begin at various distances from the flange and previous step. Where the steps (increases in tube diameter) are placed depends on the engine type, engine size, operating RPM, and other factors.
You will find a few websites that bad-mouth step-header designs as a waste of money. They claim that they do not work, the theory is bad, no one uses them, etc. You have to decide why these people are condemning this design and look for any bias in this source. Are they selling something different? Well, if the step-header designs were as crappy as these websites describe, heavily funded race teams would NOT be using them on championship winning engines. It is my opinion that there are uses and benefits from step-headers, but not every engine is going to show gains in using the design. Over the years I have talked many people out of step headers as a waste "for their specific application." I have also recommended step headers those who felt they did not need them.
A step-header is built by starting with a slightly smaller tube, then going up in size in one more (2-step), or two more (3-step) sizes. If you look at the exhaust port of your cylinder heads you will notice that they typically are NOT of the same size as your header tubes. You won't even find a header flange that is a direct match in dimension to your exhaust port unless it is a race only application that has been user/builder modified, or someone looking to spend the time and expense to fine every available horsepower. If the exhaust ports on your cylinder heads get too big you lose air velocity and torque, and take the chance of increasing the possibility reversion. As the exiting exhaust gases travel through the headers they are expanding until they cool enough to where expansion stops. The longer you can keep the exhaust velocity up, the better the scavenging of the cylinders, and the more power and torque the engine can make.
By starting with a slightly smaller tube at the cylinder head flange. This step is necessary to ensure the exhaust velocity stays UP. As the gases expand, they get to the next size, or the second step. This allows for a contained (managed) control of the expansion of the spent gases while still keeping an efficient exhaust velocity. The manufactured deign may include a third step (increase in tubing size), and then the tubes connect to the collector. This gradual increase in size provides the maximum balance of exhaust velocity and volume. The data below was created using Meaux Racing's PIPEMAX software. You can see that this is based upon a 500" (8.19L) engine with an optimum speed (where the engine will spend the majority of time) of 9,000 RPM. The example below shows the best single stage, two step, and three step header dimensions."
Bottom line you want negative pressure at the exhaust valve during overlap. Properly done header can create a much GREATER pressure drop at overlap than when the piston is descending during the intake stroke. This depression during overlap is what can give you a head start in getting the air moving in the intake port. This is a oversimplified explanation but you get the idea.
Many of you who are reading this article may never have heard of a step-header. This is because step-headers are used almost exclusively in race-only applications. A step-header design is that which has more than one size (diameter) of primary tubing. You start with a smaller header tube diameter at the cylinder head, and then have one or two larger sizes which begin at various distances from the flange and previous step. Where the steps (increases in tube diameter) are placed depends on the engine type, engine size, operating RPM, and other factors.
You will find a few websites that bad-mouth step-header designs as a waste of money. They claim that they do not work, the theory is bad, no one uses them, etc. You have to decide why these people are condemning this design and look for any bias in this source. Are they selling something different? Well, if the step-header designs were as crappy as these websites describe, heavily funded race teams would NOT be using them on championship winning engines. It is my opinion that there are uses and benefits from step-headers, but not every engine is going to show gains in using the design. Over the years I have talked many people out of step headers as a waste "for their specific application." I have also recommended step headers those who felt they did not need them.
A step-header is built by starting with a slightly smaller tube, then going up in size in one more (2-step), or two more (3-step) sizes. If you look at the exhaust port of your cylinder heads you will notice that they typically are NOT of the same size as your header tubes. You won't even find a header flange that is a direct match in dimension to your exhaust port unless it is a race only application that has been user/builder modified, or someone looking to spend the time and expense to fine every available horsepower. If the exhaust ports on your cylinder heads get too big you lose air velocity and torque, and take the chance of increasing the possibility reversion. As the exiting exhaust gases travel through the headers they are expanding until they cool enough to where expansion stops. The longer you can keep the exhaust velocity up, the better the scavenging of the cylinders, and the more power and torque the engine can make.
By starting with a slightly smaller tube at the cylinder head flange. This step is necessary to ensure the exhaust velocity stays UP. As the gases expand, they get to the next size, or the second step. This allows for a contained (managed) control of the expansion of the spent gases while still keeping an efficient exhaust velocity. The manufactured deign may include a third step (increase in tubing size), and then the tubes connect to the collector. This gradual increase in size provides the maximum balance of exhaust velocity and volume. The data below was created using Meaux Racing's PIPEMAX software. You can see that this is based upon a 500" (8.19L) engine with an optimum speed (where the engine will spend the majority of time) of 9,000 RPM. The example below shows the best single stage, two step, and three step header dimensions."
Bottom line you want negative pressure at the exhaust valve during overlap. Properly done header can create a much GREATER pressure drop at overlap than when the piston is descending during the intake stroke. This depression during overlap is what can give you a head start in getting the air moving in the intake port. This is a oversimplified explanation but you get the idea.
