The Oldsmobile Connection

[andrewk]

I thought we all might be able to learn something here-

I have always heard conflicting views from different people in this hobby, regarding headers and exhaust volume. It seemed to me the guys with more time in all said the same thing, but given the following quote-

91parkave wrote: Ive installed long tubes on a couple of cars before, and ive heard manifolds....Headers are louder than manifolds, the exact reason..im not sure of but they were louder.

Can there be any truth to this?

I always thought the purpose behind headers, other than the under-hood bragging right, was to make the removal of spent exhaust gases more efficient. Some headers do this much better or worse than others, but the good designs tune the length of the pipe to the pulse of the engine so that the scavenging effect is amplified.

I have never been able to tell a difference in amplitude between open manifolds and open headers. Open headers sound deeper to me, but manifolds are just as loud.

I haven't put a db meter on an engine, but thought it might be a good topic for discussion.

Thoughts?

[91parkave]

To the best of my knowledge Headers....when designed properly are supposed to create a vacum of some sort to scavenge exhaust gasses from their respective cylinders, faster, than manifolds will. so i guess in theory this is supposed to speed up the exhaust flow out of the cylinders, but at the same time change the tone (louder??) because of this effect, im curious to see any factual data behind this as well.

[aron115]

well i dont know much about all that technical stuff but if you thinking basic, if you have headers that are bigger and have more volume inside sounds waves will be able to travel longer from the start so by the time they get to the end of the exhaust system they may be a tad loud from the combination of more exhuast going through a bigger space and the engine exhuast noise being able to travel further before going out the end of the system

[88 Coupe]

91buickman wrote: To the best of my knowledge ........
You seem to be growing up.

91buickman wrote: ........ when designed properly are supposed to create a vacum ........
They do not "create" anything.

91buickman wrote: ........ of some sort ........
Is this the same engineering concept, that went into the design of these headers?

And inspired the following comment?

On 3800 Pro, Ron Vogel wrote: ........ I've seen much worse, a guy on the Thunderbird forums was using plumbing pipe on his.
He has probably been around more than I have.

91buickman wrote: ........ to scavenge exhaust gasses from their respective cylinders, faster, than manifolds will ........
All other factors staying the same, there should be little, if any, difference.

91buickman wrote: ........ so i guess in theory this is supposed to speed up the exhaust flow out of the cylinders ........
In some cases, headers can reduce back pressure in the same manner, and to the same extent, as dual exhausts.

91buickman wrote: ........ but at the same time change the tone (louder?) ........
Tone will vary with the size of the collector. The same can be done by changing the size of the head pipe.

91buickman wrote: ........ because of this effect ........
What effect?

91buickman wrote: ........ im curious to see any factual data behind this as well.
Then again, maybe you are not growing up. Consider the following, from your CAI hijack:

88 Coupe wrote: 91parkave wrote: ........ actually theres been many studies on how turbulent flexible tubing is. smooth bends and couplers get the best results ........ Again, cite a couple.
I asked you first.

Norm

[88 Coupe]

aron115 wrote: ........ from the combination of more exhuast going through a bigger space ........
Unless something else has changed, the volume of exhaust gases will remain the same.

Norm

[andrewk]

88Coupe wrote: They do not "create" anything.

This means that headers are merely maximizing what potential is already there, correct?

88Coupe wrote: Tone will vary with the size of the collector. The same can be done by changing the size of the head pipe.


Does using smaller head pipes only affect tone?

[88 Coupe]

andrewk wrote: ........ This means that headers are merely maximizing what potential is already there ........
Instead of mixing the pulses from each cylinder, in a manifold, they are mixed in the collector.

Due to the increased distance, it is possible that the gases might be cooler (less volume flow and velocity) when they enter the collector.

But how could that affect the corresponding sound waves?

Quote: ........ Does using smaller head pipes only affect tone?
Since the pressure and volume flow exiting the manifold are unchanged, velocity will be increased.

Reshaping it to a megaphone, or horn, could increase the sound volume.

Norm

[91parkave]

So then what about headers with stepped primaries? 4-2-1, Types?

[andrewk]

91parkave wrote: So then what about headers with stepped primaries? 4-2-1, Types?

What about them, would make them sound any different than any other header?

[91parkave]

Also thought i'd include this article for any clarifaction or to sum up anything mentioned above

This article is from Burns Stainless Headers co.



burns stainless wrote:
Before we delve into the dark art of exhaust theory, let's take a quick journey through the exhaust system from the perspective of the exhaust gases.

As the piston approaches top dead center, the spark plug fires igniting a fireball just as the piston rocks over into the power stroke. The piston transfers the energy of the expanding gases to the crankshaft as the exhaust valve starts to open in the last part of the power stroke. The gas pressure is still high (70 to 90 p.s.i.) causing a rapid escape of the gases (blowdown). A pressure wave is generated as the valve continues to open. Gases can flow at an average speed of over 350 ft/sec, but the pressure wave travels at the speed of sound (and is dependent on gas temperature). Expanding exhaust gases rush into the port and down the primary header pipe. At the end of the pipe, the gases and waves converge at the collector. In the collector, the gases expand quickly as the waves propagate into all of the available orifices including the other primary tubes. The gases and some of the wave energy flow into the collector outlet and out the tail pipe.

Based on the above visualization, two basic phenomenon are at work in the exhaust system: gas particle movement and pressure wave activity. The absolute pressure differential between the cylinder and the atmosphere determines gas particle speed. As the gases travel down the pipe and expand, the speed decreases. The pressure waves, on the other hand, base their speed on the speed of sound. While the wave speed also decreases as they travel down the pipe due to gas cooling, the speed will increase again as the wave is reflected back up the pipe towards the cylinder. At all times, the speed of the wave action is much greater than the speed of the gas particles. Waves behave much differently than gas particles when a junction is encountered in the pipe. When two or more pipes come together, as in a collector for example, the waves travel into all of the available pipes - backwards as well as forwards. Waves are also reflected back up the original pipe, but with a negative pressure. The strength of the wave reflection is based on the area change compared to the area of the originating pipe.

This reflecting, negative pulse energy is the basis of wave action tuning. The basic idea is to time the negative wave pulse reflection to coincide with the period of overlap - this low pressure helps to pull in a fresh intake charge as the intake valve is opening and helps to remove the residual exhaust gases before the exhaust valve closes. Typically this phenomenon is controlled by the length of the primary header pipe. Due to the 'critical timing' aspect of this tuning technique, there may be parts of the power curve where more harm than good is done.

Gas speed is a double edged sword as well, too much gas speed indicates that that the system may be too restrictive hurting top end power, while too little gas speed tends to make the power curve excessively 'peaky' hurting low end torque. Larger diameter tubes allow the gases to expand; this cools the gases, slowing down both the gases and the waves.

Exhaust system design is a balancing act between all of these complex events and their timing. Even with the best compromise of exhaust pipe diameter and length, the collector outlet sizing can make or break the best design. The bottom line on any exhaust system design is to create the best, most useful power curve. All theory aside, the final judgement is how the engine likes the exhaust tuning on the dyno and on the track.

Various exhaust designs have evolved over the years from theory, but the majority are still being built from 'cut & try' experimenting. Only lately have computer programs like X-design or high end engine simulation programs been able to help in this process. Practical tools like adjustable length primary pipes and our B-TEC and DynoSYS adjustable collectors allow quicker design changes on the dyno or in the car. When considering a header design, the following points need to be considered:

*
1) Header primary pipe diameter (also whether constant size or stepped pipes).
*
2) Primary pipe overall length.
*
3) Collector package including the number of pipes per collector and the outlet sizing.
*
4) Megaphone/tailpipe package.

There are many ideas about header pipe sizing. Usually the primary pipe sizing is related to exhaust valve and port size. Header pipe length is dependent on wave tuning (or lack of it). Typically, longer pipes tune for lower r.p.m. power and the shorter pipes favor high r.p.m. power. The collector package is dependent on the number of cylinders, the engine configuration (V-8, inline 6, etc.), firing order and the basic design objectives (interference or independence). The collector outlet size is determined by primary pipe size and exhaust cam timing.

[andrewk]

88 Coupe wrote: But how could that affect the corresponding sound waves?

Wouldn't the sound waves be moving faster and before the gases move from the cylinder?

I don't think it would affect the sound waves at all-

[andrewk]

91parkave wrote: Also thought i'd include this article for any clarifaction or to sum up anything mentioned above

This article is from Burns Stainless Headers co.


How does that article, on the design of headers, clarify, sum up anything, or have anything to do with what is mentioned above, regarding the thread topic? (Which is the discussion of whether or not headers make a car louder)

If you would like to discuss header design, or how they work, you are more than welcome to start a thread about it.

[91parkave]

andrewk wrote: 91parkave wrote: Also thought i'd include this article for any clarifaction or to sum up anything mentioned above

This article is from Burns Stainless Headers co.


How does that article, on the design of headers, clarify, sum up anything, or have anything to do with what is mentioned above, regarding the thread topic? (Which is the discussion of whether or not headers make a car louder)

If you would like to discuss header design, or how they work, you are more than welcome to start a thread about it.

Think outside your box, Everything you and 88 brain cells have been discussing, Cylinder exhaust pulses ,etc....just to name a few, are all in this article, how do you not see that? Not to mention wouldnt a clear perspective on how headers work give a clearer picture to better understand the topic at hand?

[andrewk]

Quote: Think outside your box, Everything you and 88 brain cells have been discussing, Cylinder exhaust pulses ,etc....just to name a few, are all in this article, how do you not see that?

I wasn't trying to be semantic.

We never were discussing "Cylinder exhaust pulses ,etc". The information that was provided on them by Norm was more than enough than we needed for the topic, in order to determine whether or not headers make a car louder. They don't.

The reason I posted that is because a more in depth discussion on that, or any other article regarding the design for headers, is a subject for a different thread, and it could make for some good discussion. That's all it meant- nothing more, nothing less.

Quote: Not to mention wouldnt a clear perspective on how headers work give a clearer picture to better understand the topic at hand?

A new topic would put the focus on that facet of discussion, rather than just lump it in with another subject. This would make using and/or finding the information later easier. It seems you haven't figured that out yet.

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Returning to topic, here it is again-

Quote: So then what about headers with stepped primaries? 4-2-1, Types?

What about them, would make them sound any different than any other header?

[91parkave]

Understood. I wasnt calling you out or anything, just trying to understand where your coming from. Going back to the discussion of Sound levels though, I was ^asking^ if 4-2-1 designs or stepped primary designs, offer more sound db's over a regular header or manifold design.