Header with "bridges" idea

[BoostedDrummer]

Hey guys,


The more I read up on headers and exhaust design, what with scavenging and all that stuff, I keep having these ideas that come to mind that just make me wonder more and more on certain things that I have never seen and I think might work.. although, I am a newb when it comes to technical flow stuff and exhaust pulse energy and whatnot.. so I assume there is a little magical wizard in my exhaust who makes my turbo spin faster.

I drew a simple exhaust header just to illustrate my idea based off the firing order of our cars. My idea being that if there were some exhaust "bridges" leading from one primary that is currently flowing exhaust out to another primary thats next in line on the firing order, the exhaust from the fired primary would help get a pre flow of gasses heading toward the collector in the "next in line" primary. I'm essentially thinking of it as an in place vacuum of sorts. My thinking is that while one primary is filled with exhaust gasses, the others are basically neutral unless they are being scavenged somehow. Eventually I would like to start making my own header designs, not to sell of course, but for fun and learning. Please take a look at my illustration and let me know if there actually is something plausible about this. Please remember that I was just a C+ student in high school and I isn't the one of the smarts

Yellow represents the primary thats currently pushing out exhaust while blue represents the "next in line" primary. The red arrows represent exhaust flow direction.

[turismolover22]

From designs "pulled" from some of the big block headers, it would appear that the bridges idea isnt necessary. From what i understand, the headers and exhaust tubes are welded and made to certain lengths, so that instead of an equal length header style, the exhaust gases are "timed" so that with each pulse or fire, the gases are hitting the collector right after each other. Obviously with a big block or any v motor, the pulses are in an odd order and not "sequential" to each other. If any of my ramblings make sense, please correct anything imay be wrong on.Interested to see how this turns out. With an n/a motor, i can see this being more beneficial. But with forced induction, it would seem we concentrate more on flow than on scavenging.Has anyone tried using a conical type tube for a header, so that when the gases reach the collector, they are at a higher/equal velocity than exiting the head? I know this couldbe applied to an intake, to increase air speed into the motor, can it be applied to the exhaust, to push air faster over the turbine, to potentially decrease spool time?

[Rrider]

Damn you "drew" that idea pretty nicely. :P

[Ondonti]

I am thinking that the volume you are flowing through the small tube will hurt performance because you would take away the effect the main exhaust pulse has as it hits the collector and draws on the other runners. It would probably be impossible for both routes to hit the collector at the same time and that would also hurt performance (including turbo spool). These losses would not make up for potentially zero gains from the small tubes.

People seem to want the longest possible runners that are reasonably fitted which maximizes the effect of what I said above that your design hurts. You would probably turn the exhaust manifold into something that acts more like a log manifold but for way more money and and durability concerns.

So what I am saying is, a tubular manifold properly designed does exactly what you are trying to do. I think your idea will make things worse or just super expensive "exactly the same" performance wise.


I am still tempted to put exhaust evac valves pre-turbo to inject oxygen into the exhaust manifold pre turbo but I sorta doubt I could pull off what is needed to make that work. Crazy idea that would not work at worst and blow turbos at best :P

[BoostedDrummer]

This is good. Again, I'm just throwing this out there as a learning experience, not an actual product lol :P

I wasn't thinking of the small "bridge tubes" to be quite as large as whats on the drawing, I just made them that size to illustrate the concept. If I were to actually make something like this for the heck of it, I'd have them be more along the size of brake line tubing.

I am thinking that the volume you are flowing through the small tube will hurt performance because you would take away the effect the main exhaust pulse has as it hits the collector and draws on the other runners. It would probably be impossible for both routes to hit the collector at the same time and that would also hurt performance (including turbo spool). These losses would not make up for potentially zero gains from the small tubes.

All the gasses eventually head toward the same focal point though, and if the bridges main job is to carry a small pressure wave into the next primary in order to "prime" it, then it should have a positive effect right? I was thinking of it like this, say youre at a hookah bar or even smoking a cigarette and you fill your mouth with smoke. You open your mouth but dont let any smoke out and it just sits there. If I passed my hand rapidly in front of it, some would come out. I recognize this as the scavenging effect I've read about.

For the bridges idea, think of a your kitchen sink filled up with water. As you pull the drain plug out, the water is draining at an amount that the drain opening allows given its size. Now think of the little spray nozzle thats on the side of the sink, you know, the one your wife told you to stop playing with when youre washing the dishes. If you took that and put it under the water and focused the water coming out of the sprayer directly down the drain, it should force the surrounding water to follow since you are, in effect, causing the drain to become a low pressure area. This should, theoretically, cause the sink to drain faster than if it was just being drained via gravity. I don't have a sink with a nozzle out here in the desert to test this or time it, but there's nothing wrong with throwing out a hypothesis

[Reaper1]

If the manifold is designed to actually scavenge, then these tubes aren't needed. The pressure wave that you are looking for to "prime" the next runner is actually the reflected exhaust pulse from the previously fired cylinder. If the runners are made to the correct length, then this pressure wave will do exactly the job you are wanting.

There is a caveat to this: tuned length runners only work under the conditions they were designed under. Any variation in rpm or temperature will alter the length needed for the runners to be "tuned". This is why most people don't bother with making tuned length headers for turbo applications. The temperature varies too much for the design to be worth anything except in the one condition they were designed for.

That being said, equal length runners (not the same as tuned length runners) *can* be a benefit to turbo applications because then the pulses will reach the turbine with the same amount of time between "hits" and this can have the effect of helping spool the turbo faster.

[5DIGITS]

If the manifold is designed to actually scavenge, then these tubes aren't needed. The pressure wave that you are looking for to "prime" the next runner is actually the reflected exhaust pulse from the previously fired cylinder. If the runners are made to the correct length, then this pressure wave will do exactly the job you are wanting. There is a caveat to this: tuned length runners only work under the conditions they were designed under. Any variation in rpm or temperature will alter the length needed for the runners to be "tuned". This is why most people don't bother with making tuned length headers for turbo applications. The temperature varies too much for the design to be worth anything except in the one condition they were designed for. That being said, equal length runners (not the same as tuned length runners) *can* be a benefit to turbo applications because then the pulses will reach the turbine with the same amount of time between "hits" and this can have the effect of helping spool the turbo faster.

This is very well said !