Thanks for the long post.
enigma57 wrote:Some things we learned and ran up against......
* Allow end of collectors to extend 2" to 3" into termination chambers. Same for exit pipe at opposite end.
* Ideally, you want each termination chamber to have volume equal to twice the displacement discharged into it. More doesn't hurt and even if you cannot get more than 75%, its worth the effort.
* Entire interiour volume of termination chamber (less volume taken up by entry and exit pipe stubs extending into chamber at either end) counts towards necessary volume.
* Muffler(s) should be located downstream of chambers (can be directly behind chambers or anywhere between ends of chambers and ends of exhaust system.
* Chambers can have round, oval, square or rectangular cross section. And a square cross section of same size as a round cross section will obviously have greater interiour volume for same length. However...... In actual practice, we found straight sided (square or rectangular) chambers of same wall thickness are more likely to flex, work harden and be affected by metal fatigue over time than round or oval cross sections.
* Final configuration...... We pulled round termination chambers and hand drilled beaucoup 3/16" diameter holes in them (360 degrees on 3/4" spacing to within 1" of each end). This took a while and was no fun at all. When done, we made new end caps (like large flat washers) to accommodate larger outer shell 7" in diameter, slid one over front stub and welded it in place, leaving original cap and the tubing we had drilled in place. Slid outer shell over tubing that we drilled and welded outer shell to front end cap. Then went to a machine shop where they had lots of stainless steel shavings they had saved for us and packed them into the annular space between tubing we drilled and new outer shell using a piece of 3/4" square bar stock a couple of feet longer than our new outer shell. Once we had it packed tight in each, we slid the washer shaped rear end cap piece over stub and welded it in place. The end result was that we made our termination chambers double as straight through steel packs in addition to the DynoMax Super Turbo mufflers we already had just ahead of rear bumper. These DynoMax mufflers were sized for flow and gave us the 2.2 cfm per HP recommended by David Vizard for zero sum loss muffled exhaust system. It was still pretty throaty when you got on it but was quiet enough not to drive you nuts on long trips and not loud enough to draw unwanted attention from police.
* Crossover (balance) pipes connecting left and right bank...... We found no advantage between 'X' type and 'H' type so long as 'H' type was same size as collectors. Crossover pipe can be placed anywhere after primaries enter collectors and it can even be placed between termination chambers if you wish. We placed ours about 6" behind front of termination chambers. Later added a 2nd crossover joining left and right side tailpipes behind chambers in area just before top of bend going over rear axle. Each crossover pipe seemed to help lower noise level a bit and smoothed out exhaust note some, as well.
* One thing we found on chassis dyno regarding full length muffled exhaust was that if your pipe size is sufficient for power generated but you cannot get flow you need through mufflers any other way...... By using tube size increasers/reducers (like a bell reducer), if you install free flowing mufflers having one size larger internal flowpath than pipe system size...... They will flow same as if you ran straights (no mufflers). But they will be louder than mufflers same size as pipe system.
It seems to me that the extending the pipe inside the expansion chamber changes the frequency response in a major way. The simple expansion chamber gives a transmission loss that even I can kind of understand intuitively.
SimpleExpansionChamber.png
Expanding the pipe inside the expansion chamber seems to retain some of the weak spots of the shorter chamber, but there's now an extra frequency that gets muffled really well:
LongerChamberWithExtendedInlet.png
Somehow pipe extension into the expansion chamber that is 1/3 of the total chamber length resulting in 2/3 of free chamber length before outlet really kills that one frequency extremely well.
I'm not sure if we should think about the volume of the chamber or think about the length and the diameter separately. I'm currently thinking that the length detemines what frequencies the expansion chamber muffles and the diameter how much it muffles them. More specifically, I think that h=(m-1/m)^2 where m is the inlet area (in this case the same as outlet area) divided by the chamber cross-sectional area is the measure that seems to drive the magnitude of muffling. So bigger pipe needs a bigger can (shocker there).
One question is that if you have a 3" pipe and run that to a perforated core with 5" diameter and then put that inside a 7" pipe with fiberglass or stainless shavings packing, does the sound wave see that more as a 5" diameter expansion chamber or as a 7" diameter expansion chamber?
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