Step Headers

[Scruffage]

Will someone please explain this new step header phenomenon to me? What's the engineering behind this?

[MarylandSpeed]

The stepped design is when a header has primaries that expand from one size to another over their length. With Kooks new headers, the primaries start as 1 3/4" and then a 3rd of the way down the primary expand to 1 7/8". This has an effect kind of like a pinched hose where it increases the exhaust velocity. The faster the moves through the header, the better the engine breathes, and the more power it makes. They do however cost more because of the extra work. So you have to decide if the gains are worth the cost.

Here are pictures of the Kooks Signature Series Stepped header. They had this at PRI and it is the one we tested on our car.

[Apex Motorsports]

Stepped headers are designed to optimize scavenging and create more power and a broader torque curve than standard straight tube headers. The stepped design is acoustically tuned specifically for their application, some math is involved in order to get it right so you can't just put a step any old where you like. I am no expert but the theory behind it has to do with creating a sonic pulse within the tube that increases velocity and scavenging. Below is a picture of the new Stainless Works stepped headers.

[14pilot]

Originally Posted by Apex Chase

Stepped headers are designed to optimize scavenging and create more power and a broader torque curve than standard straight tube headers. The stepped design is acoustically tuned specifically for their application, some math is involved in order to get it right so you can't just put a step any old where you like. I am no expert but the theory behind it has to do with creating a sonic pulse within the tube that increases velocity and scavenging. Below is a picture of the new Stainless Works stepped headers.

Yes, when the shock wave from the exhaust valve opening travels across the step, it reflects back towards the exhaust valve creating a negative pressure. It's like the waves caused by throwing a rock into water, when the waves hit something like the edge of a pool, they reflect back, except in an engine this happens 50 times per second at 6,000 rpm.

When the step(s) are at the correct length for the application, this wave of negative pressure assists scavenging of the next exhaust cycle by pulling it out into the pressure drop created. The negative pressure could be something like 3-5 PSI at the exhaust valve. This is usually at tuned length of either the HP peak rpm of the engine for a drag car, or the mid-range operating rpm of a street or road race car.

This same effect happens in all exhaust systems. The step in primary diameter just increases this effect. If done wrong, the reflected pressure wave could be positive pressure instead of negative pressure. This would result in pushing some of the air-fuel intake charge back up into the intake track.

[ducq]

Originally Posted by 14pilot

Yes, when the shock wave from the exhaust valve opening travels across the step, it reflects back towards the exhaust valve creating a negative pressure. It's like the waves caused by throwing a rock into water, when the waves hit something like the edge of a pool, they reflect back, except in an engine this happens 50 times per second at 6,000 rpm.

When the step(s) are at the correct length for the application, this wave of negative pressure assists scavenging of the next exhaust cycle by pulling it out into the pressure drop created. The negative pressure could be something like 3-5 PSI at the exhaust valve. This is usually at tuned length of either the HP peak rpm of the engine for a drag car, or the mid-range operating rpm of a street or road race car.

This same effect happens in all exhaust systems. The step in primary diameter just increases this effect. If done wrong, the reflected pressure wave could be positive pressure instead of negative pressure. This would result in pushing some of the air-fuel intake charge back up into the intake track.

I think we'll all take your word for it :P

[Scruffage]

Originally Posted by 14pilot

Yes, when the shock wave from the exhaust valve opening travels across the step, it reflects back towards the exhaust valve creating a negative pressure. It's like the waves caused by throwing a rock into water, when the waves hit something like the edge of a pool, they reflect back, except in an engine this happens 50 times per second at 6,000 rpm.

When the step(s) are at the correct length for the application, this wave of negative pressure assists scavenging of the next exhaust cycle by pulling it out into the pressure drop created. The negative pressure could be something like 3-5 PSI at the exhaust valve. This is usually at tuned length of either the HP peak rpm of the engine for a drag car, or the mid-range operating rpm of a street or road race car.

This same effect happens in all exhaust systems. The step in primary diameter just increases this effect. If done wrong, the reflected pressure wave could be positive pressure instead of negative pressure. This would result in pushing some of the air-fuel intake charge back up into the intake track.

So the distance the step is from the head is very critical and will determine how much pressure drop is created or if incorrect may cause back pressure. So are you only seeing a benefit in scavenging every other exhaust cycle per cylinder?

[14pilot]

Originally Posted by Scruffage

So the distance the step is from the head is very critical and will determines how much pressure drop is created or if incorrect may cause back pressure. So are you only seeing a benefit in scavenging every other exhaust cycle per cylinder?

Benefit happens every exhaust cycle. The pressure (shock) wave is not the exhaust gases themselves. The wave contains no mass, it is just energy traveling at roughly 1,500 feet per second. Going so fast that the wave actually reflects multiple times back and forth between the 'step' and the back of the exhaust valve between exhaust valve openings. The distance of the step from the exhaust valve determine at what RPM that the negative pressure wave (vacuum?) will be greatest at.

These shock wave reflections or pulses if you will, happen in non-step headers, as any time the wave traveling down the exhaust tubing hits anything that disturbs it, the disturbance causes the wave to reflect. So a sharp bend, mis-aligned tubes, poor weld, the collectors, a H or X pipe, the muffler and the exit of the exhaust at the tips all cause reflections to go back up into the system. Step headers are used to create a very strong reflection (pressure drop) as they are so close to the exhaust valve pocket.

The wave reflections from one cylinder also travel up into the other primaries too. So the design for one cylinder has to account for not spoiling the scavenging in other primary tubes. Lots going on here.

Some Step designs use 2 or 3 steps in the primary to attempt to have a broader power band by having multiple RPM ranges benefiting from the effect. My Harley V-Rod exhaust has 3 steps in it and works very well.

Some header designers will also combine Stepped primaries with larger than recommended primary tube diameters attempting to have broad TQ range from the wave reflections and the peak HP effect from the larger diameter tubes. My V-Rod is such a design, exiting the head at 1.75", then stepping to 1.88" at 9", then stepping to 2" at 9", and finally stepping to 2.125" before it hits the 3.5" collector. Very large tubing diameters here, but I didn't give up any low end TQ due to a sucessfully design. Note that this took over 2 years to perfect and many hours of testing and dyno time.

BTW: Step headers have been around for decades. Guys like Eds, Stahl, Lemmons and others have been playing with stepping headers for like 40 years, maybe more than that. Not all are fans though.

[NVMYSS]

Is ARH working on a set of stepped headers as well? Or just SW and Kooks?

[GEEo]

how much is the price difference between the normal headers and the stepped one??

[Mark Myles]

Holly Shit! lol.....nice!


M

[Scruffage]

Originally Posted by 14pilot

Benefit happens every exhaust cycle. The pressure (shock) wave is not the exhaust gases themselves. The wave contains no mass, it is just energy traveling at roughly 1,500 feet per second. Going so fast that the wave actually reflects multiple times back and forth between the 'step' and the back of the exhaust valve between exhaust valve openings. The distance of the step from the exhaust valve determine at what RPM that the negative pressure wave (vacuum?) will be greatest at.

These shock wave reflections or pulses if you will, happen in non-step headers, as any time the wave traveling down the exhaust tubing hits anything that disturbs it, the disturbance causes the wave to reflect. So a sharp bend, mis-aligned tubes, poor weld, the collectors, a H or X pipe, the muffler and the exit of the exhaust at the tips all cause reflections to go back up into the system. Step headers are used to create a very strong reflection (pressure drop) as they are so close to the exhaust valve pocket.

The wave reflections from one cylinder also travel up into the other primaries too. So the design for one cylinder has to account for not spoiling the scavenging in other primary tubes. Lots going on here.

Some Step designs use 2 or 3 steps in the primary to attempt to have a broader power band by having multiple RPM ranges benefiting from the effect. My Harley V-Rod exhaust has 3 steps in it and works very well.

Some header designers will also combine Stepped primaries with larger than recommended primary tube diameters attempting to have broad TQ range from the wave reflections and the peak HP effect from the larger diameter tubes. My V-Rod is such a design, exiting the head at 1.75", then stepping to 1.88" at 9", then stepping to 2" at 9", and finally stepping to 2.125" before it hits the 3.5" collector. Very large tubing diameters here, but I didn't give up any low end TQ due to a sucessfully design. Note that this took over 2 years to perfect and many hours of testing and dyno time.

BTW: Step headers have been around for decades. Guys like Eds, Stahl, Lemmons and others have been playing with stepping headers for like 40 years, maybe more than that. Not all are fans though.

Very good info, Thanks.

I would like to see some dyno numbers and price to evaluate cost vs gains.

[A.R. Headers]

Guys, The advantage of stepped headers are affected dramatically by the balance of the exhaust system. 14Pilot did a great job explaining why. Stepped headers will work best on open header applications. We build stepped headers all the time and with all the correct information we can custom build a set for you.
The reality is that with cats and about 20ft of pipe afterwards the rewards of stepped headers will be neglegible at best. If you plan on racing your car and will be running with open headers when doing so, then call me and we'll build you a step header that's made to work perfectly with your combination of mods. We can even build triple step headers and adjust the primary lengths to suit.

Nick
A.R. Headers

Nick

[Scruffage]

Originally Posted by A.R. Headers

Guys, The advantage of stepped headers are affected dramatically by the balance of the exhaust system. 14Pilot did a great job explaining why. Stepped headers will work best on open header applications. We build stepped headers all the time and with all the correct information we can custom build a set for you.
The reality is that with cats and about 20ft of pipe afterwards the rewards of stepped headers will be neglegible at best. If you plan on racing your car and will be running with open headers when doing so, then call me and we'll build you a step header that's made to work perfectly with your combination of mods. We can even build triple step headers and adjust the primary lengths to suit.

Nick
A.R. Headers

Nick

I'm not looking to do any racing. I'm just researching before I make my header purchase. Trying to get the most out of a header upgrade. Do ARH headers have the merge spike in the collector and what HP gains are you seeing on a LS3?

[bob vogel]

[QUOTE=A.R. Headers;2719769]Guys, The advantage of stepped headers are affected dramatically by the balance of the exhaust system. 14Pilot did a great job explaining why. Stepped headers will work best on open header applications. We build stepped headers all the time and with all the correct information we can custom build a set for you.
The reality is that with cats and about 20ft of pipe afterwards the rewards of stepped headers will be neglegible at best. If you plan on racing your car and will be running with open headers when doing so, then call me and we'll build you a step header that's made to work perfectly with your combination of mods. We can even build triple step headers and adjust the primary lengths to suit.

Nick
A.R.
thank you very much for this info . now this makes more sense to me..