Stepped Primary Exhaust Extractors 

Indeed

still trying to get my head around the idea

Shit .... Me too . I thought I found one far enough down the list 😂

​@@vercingetorige400think of sound waves being bouncy balls and the stepped headers being a wall of teeth .... Once that bouncy ball of sound hits the wall of teeth, it bounces back and splits into more bouncy sound waves That are only half the size but are moving twice as fast

So does the sound work in conjunction with a particular firing order?

My man!! ❤

same

Oddly enough same here

I love a nice 2-stroke exhaust note. God, I miss the days when those smoky little torque monsters were a dime a dozen.

Same principal, but on a 4 stroke the step is increasing the negative pressure behind the wave. Sucking out the cylinder. You don't want a high pressure wave pushing into that cylinder during overlap. Also like a two stroke the lengths are critical to valve timing.

Where do I go to learn more about this? Step location, size of increase at step, number of steps etc.

Yep. This is how tuned port injection works. You can increase the VE (volumetric efficiency) to greater than 100%. Meaning you can ‘boost’ your engine or in other words, pressurize your intake air. This uses math to calculate the wave speed based on air temp, air density, and wave speed. Once the speed is known, you can use this to calculate how long your runner has to be for the wave to travel to the end and reflect back. The way to supercharge is to have that pressure wave arrive at the back of the valve the second the valve opens. This creates a pressure pulse that is additional to the manifold pressure and higher than the negative pressure in the cylinder. Causing a greater delta, increasing airflow speed and density. Bingo, you used math to boost an engine. The issue here is that this length is fixed. And only performs well within a very narrow rpm band. Causing a very peaky performance. (See GM TPI) And sometimes, the RPM that are frequency multiples get some of the same effect. So if you tuned it for 2000rpm, you would see some increase at an octave above, or 4000rpm. While at other rpm, it is technically possible to revert air back to the intake manifold instead of the back of the valve. This would be bad, obviously.

It's not the opposite ?

fabrication? And you have to remember that the inside of the pipe does look different than the outside. But if we think about the sound. The radius of the bend (step if you will) does not matter if the lenght of the sound wave is (if I remember correctly) twice the diameter of the radius. So in header scale it does not really matter. For the flow of the gas it does matter if the pipe is smooth, it generally flows better. But as the exhaust gasses are resonating a bit of turbulance might even be beneficial in some situations. It's way over my head thou.

You can see on the lower pipe it has a belled end flange to make it easier to weld. Stepped headers are very hard to build cleanly by not contaminating the inside o f the pipe.

I dont know much but from maisters video it must be done before the collector so each cylinder’s exhaust gases can be amplified once by the step and then again once they reach the collector.

Headers have to be tested on a dyno (combined with anything else that's changed), perfect simulation require data that's hard to determine, so in the end it's quicker and more precise to test if it's of benefit for the specific combination (as well as where they should be, and a number of other things).

I dont think it would have any significant effect

Yes. You just have to realize that the turbo or open wastegate ends up being the terminating point to the wave. That's why it's good to have a secondary coming off of the collector before the turbo - but of course the downside is on the street when the exhaust plumbing can cool it'll introduce a bunch of lag until the primaries and secondaries get hot.

And you need to pay attention to the cam.

hana

No. Uneven headers kill a balanced I6. The only way you get tthat good sound and choppy rumble from a subaru is only enhanced by the headers. On an e46/the M5x platform a set of good even length catless headers make way more benefit than uneven length.

@@MarcusPinhow would you achieve that f1 sound on an I6 then dying to build some headers for my n52 now

I've wondered this, I can't seem to find anyone on RU-vid who has done it, I'm sure it would sound like one but it won't rev as high of course.

Would love to see it on a v6. I have heard some v6s that sounded a teeny tiny bit like v12 but lacked that _something_ . It may be the missing piece of the puzzle

Seconding this, I want to hear it on a 4 Cylinder car motor.

@@Mortal_3j4 That *something* is probably an extra 6 cylinders lol

@@fancyfox3602 lmao, true

You need to press that sideways triangle in the center of the video.

In short. Stepped headers do not cause a high pitched sound. They improve scavenging in the pipe, which when the pipes are all tuned length and put into proper merge collectors with even more scavenging, will make a beautiful sound. Every entire race exhaust ever is built with scavenging in mind, so it's nothing new. Some scavenge better without that design or hence sound. Which is why it had its time and isn't seen much anymore. People like Burns Stainless have known this for years. They have said you could - and they have built one - a header system that is constantly tapered to keep stepping up and up and up all the way along its length. But time and cost do not make this beneficial.

Any sudden change in diameter will change velocity. The change in diameter and velocity creates a pressure wave reflection point. This design does not change the sound of the engine in any significant way. All exhaust designs will only produce optimum performance within a small window of RPM due to gas volume and velocity vs pipe diameter and length. The stepped design, when done correctly, will give a slightly broader RPM range with a higher level of efficiency due to reduced pumping losses and less intake charge contamination due to the pressure wave/pulse/reflection tuning that assists cylinder scavenging.

​@@jdoe9518Isn't sound itself just pressure waves? It should have some effect