Cone_Junky wrote:
Sounds like you want to build a resonator/front muffler out of a megaphone welded to a glass pack. Your theory is that the megaphone going into the glasspack will "tune" the exhaust more than just the glasspack alone (correct?)
I don't see how that little difference will give any noticeable results. I think a glasspack flows better than the typical front muffler anyway, so no need for a megaphone.
Not so much that the megaphone+glasspack will work better than just the glasspack, I'm just interested in if/how the megaphone would work, placing it upstream of the glasspack just makes sure that the exhaust pulses have passed through as little as possible. Ideally, it would even go upstream of the cat, but without designing /fabricating a new header, that's not possible. I know that the exhaust works as a system rather than just a collection of components, but the root of my question lies is less about how the system as a whole works, and more about whether exhaust tuning theories from tuning a single cylinder 4 stroke could carry over to tuning a multi-cylinder 4 stroke, or would things that work fine on a single cause successive exhaust pulses fight each other (aka one reflected pressure wave hitting the successive one) and cause a metric E36 M3 ton of backpressure right at the header that wasn't present in the factory system
Slyp_Dawg
Since no one else has ventured into the 'tunability' I will. The meagphone ahead of your packed core will do 2 basic things. The megaphone will slow the flow down and allow more heat energy to be transferred to the front end of the packed core. Reducing this energy will reduce the volume at the exhaust exit more than just having the flow go thru the same packed core. The expansion at the megaphone, when used at the exit of a system, effectively acts as an extractor. The gasses are expanded and help to draw the rest of the xhasut (if done prpoerly). That tends to increase the volume at the exhaust exit since the amount of energy removed to the system is reduced by increasing flow speed.
The idea of thinking in terms of a musical instrument is not a bad one, just try to keep inmind the energy side of the system as well. The energy changes with rpm, mixture, exhaust temp and a f ew others. Most musical instruments are intended to be played at a reasonable constant by comparison. This difference is why exhaust systems are notoriously hard to design to be 'perfect' at all times...
So, in theory, I could make the packed core more effective at sound-attenuation by increasing the inner diameter of the reverse cone (aka the outlet of the reverse cone+megaphone assembly being larger diameter than the inlet) and increasing the diameter of the perforated tubing in the packed core (at least at the front of said packed core) to match? Based on my understanding of fluid flow through a cylinder (hold fluid volume constant, expand cylinder ID, and fluid velocity/pressure will decrease, opposite effect if you taper down the cylinder), it makes sense, since the exhaust gas will spend more time in/around the packing, allowing the packing to absorb more energy out of the exhaust.
Unless you meant volume as in "volume of a solid/liquid/gas", not volume as in decibel, in which case I'm lost.
