Header comparison (1-3/4" vs. stepped)
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From: Gateway International Raceway
What is the point of stepped headers? Not busting just want to know what the result is supposed to be...rationale behind the stepped header? I am using 1 7/8th kooks.
Last edited by ExceSSive; Dec 19, 2007 at 08:00 PM.
i picked up 1/8" at the primary, 1/4" where they are stepped a few inches down the primaries, and then a whole 1/2" at the collector. the big cube motors, especially ones built for FI, love that kind of pick up/flow/volume.
imagine 1/8" at the primary x 8 primaries(another 1"), 1/4" x8 primaries(2")...thats a lot more volume/velocity than what it looks like on paper.
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iTrader: (13)
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From: Gateway International Raceway
im no expert, but i would guess volume and velocity. i went from 1-3/4 all the way to a 3" collector, to a 1-7/8 stepped to 2" to 3.5" collectors.
i picked up 1/8" at the primary, 1/4" where they are stepped a few inches down the primaries, and then a whole 1/2" at the collector. the big cube motors, especially ones built for FI, love that kind of pick up/flow/volume.
imagine 1/8" at the primary x 8 primaries(another 1"), 1/4" x8 primaries(2")...thats a lot more volume/velocity than what it looks like on paper.
i picked up 1/8" at the primary, 1/4" where they are stepped a few inches down the primaries, and then a whole 1/2" at the collector. the big cube motors, especially ones built for FI, love that kind of pick up/flow/volume.
imagine 1/8" at the primary x 8 primaries(another 1"), 1/4" x8 primaries(2")...thats a lot more volume/velocity than what it looks like on paper.
I could be wrong here but I thought if you could fit more volume then the velocity would be lower...like a water hose...pressure from a fire hose down to a garden hose will make it come out faster and harder but not flow as much...go from garden hose to fire hose and the pressure reduces as there is more volume to fill up. Where are the engineers in this place? Seems there is always one of those guys around until you need one. I see how it decreases the amount of restriction but at what point do you need that? Should I have gone with a stepped to 2" for my 408? Now I wonder...
BTW...thanks to the original poster for the info and I hope to see your new heads/cam setup results...wish you could do it with the other headers and then swap again to compare both ways.
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From: Orange Park/ Jacksonville, FL
I could be wrong here but I thought if you could fit more volume then the velocity would be lower...like a water hose...pressure from a fire hose down to a garden hose will make it come out faster and harder but not flow as much...go from garden hose to fire hose and the pressure reduces as there is more volume to fill up. Where are the engineers in this place? Seems there is always one of those guys around until you need one. I see how it decreases the amount of restriction but at what point do you need that? Should I have gone with a stepped to 2" for my 408? Now I wonder...
BTW...thanks to the original poster for the info and I hope to see your new heads/cam setup results...wish you could do it with the other headers and then swap again to compare both ways.
BTW...thanks to the original poster for the info and I hope to see your new heads/cam setup results...wish you could do it with the other headers and then swap again to compare both ways.
So, I'm assuming that after I install the heads and intake, I will have a need for the extra volume. Right now, the extra volume isnt hurting, but isnt really helping either. I think a lot of it has to do with the fact that I have a VERY low restriction exhaust (3" td's with 1-chamber flowmasters). So at my power level, the 1-3/4" headers were not a restriction, therefore the stepped headers didnt have any effect on power. I didn't want to jump to a full 1-7/8" because I was always told that it was too big, and that I wouldnt need that unless I was FI, bigger cubes, or at least HUGE H/C combo. Neither of which I have. But then again, I ignored that advice when I was told the same about running a 3" td setup too, but with my cam, it seems to be working out just fine. So who knows?
Anyways, thanks! Hope to have results from the head swap in a couple of months!
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Guys, the deal with the stepped header is the benefit of the larger tubes while trying to maintain velocity. The critical area is where the primary makes its first bend. This is where reversion is going to occur. The smaller tube size off the flange helps to reduce reversion.
I have a tapered header on my sportbike and the company that makes it said it very well. When the exhaust enters the first bend the exhaust is forced against the outside wall of the pipe and it tends to reverse on the inside wall of the pipe, just like a river when water flows backwards when it enters a bend.
I would like to see automotive headers use this design. Instead of making the 1st part of the primary smaller, make it oval or tapered to keep velocity up but keep the overall diameter the same.
I have a tapered header on my sportbike and the company that makes it said it very well. When the exhaust enters the first bend the exhaust is forced against the outside wall of the pipe and it tends to reverse on the inside wall of the pipe, just like a river when water flows backwards when it enters a bend.
I would like to see automotive headers use this design. Instead of making the 1st part of the primary smaller, make it oval or tapered to keep velocity up but keep the overall diameter the same.
