Sometimes "X" pipes can create drone by retuning the "pitch" of the exhaust. The combo of that PLUS more power is likely your culprit. FWIW, Because bigger cams have more duration, they are obviously open longer. That provides more "exposure" to hearing what's going on inside the motor....which is part of "the power" element of the sound increase. More force through the pipes too...

You COULD try a cheaper test before moving the mufflers. Figure out a way to clamp something (even as cheap as heater vent tubing) to your mufflers...or their outlets. Make it long enough to extend beyond the rear of the vehicle. I actually used band clamps and dryer vent material as an extra shield -- against head -- to get my open-header engine to the exhaust shop in 2010. It was cheesy but they stayed on there until I revved it at the shop! LOL

Then you can return the pieces for a refund!....and know if your termination point is really a problem. If that's not it, consider installing some Magnaflow bullet (metallic) cats off the header couplers. I think that would cure it....especially with the description of what you liked when it was stock.

 

Sounds like you're on the right track. Going up a size in pipe does introduce some more sound effects... Greggpenn pretty much said what I would have so, rather than repeating, I'll ask another question. Where abouts in Jersey are you? We may have crossed paths once before just driving around lol.

Edit: almost forgot, you could also try turn downs on the end of the muffler tips. Supposedly that's why the stock 84s were like that... helped with resonance or something. I didn't really notice a difference.

 

Take a look at this exhaust comparison PPT from Marc Haibeck the LT5 guru. Of course this is LT5 specific, however a few things can be learned about exhaust efficiency, drone, performance and some comparisons between popular solutions. I enjoyed this study and maybe you will too.

After reading this article I was able to make a few decisions for both my ZR1 and '89 exhaust that made me happy. On the LT5, I swapped out the restrictive resonator for a MF "X" pipe to go with the MH chip. On the 89, I removed the pre-cats, swapped for a new Hi-perf catalysis. In both cases I left the factory mufflers. I have zero (zero) drone and a nice pick up in exhaust tone that sounds "adult." Thanks Marc for doing the home work.

BTW.... as we have been discussing drone, the study shows that the way to reduce (eliminate) drone is through "pressure wave cancellation" which OEM and Corsa does/

Again... this is LT5 specific, but you may pick up a few exhaust nuggets.
http://www.zr1specialist.com/HAT%20W...%20Systems.pdf

 

OK...I will say it. The PPT is nice but doesn't address drone and why it happens. No discussion of wave cancellation either...or why muffler "X" might be better at it than the next. I wish I spent more time in the Z forum because I'd also know how much of a "guru" you're talking about.

I'll grant that he's been exposed to lots and lots of combos and it's a great PPT in terms of viewing some detail in the choices. At you point out -- from a Z ownership perspective, it's helpful in picking from OEM combos. Some of it is a bit muddied toward the end (resonators), but that's OK. Again, pictures are good.

I will say it's nice you also like that Magnaflow (MF) x-muffler I referenced earlier in this thread. Sounds like it's good on a Z too!

As for dropping the '89, the consensus of the C4 forums is L98 mufflers aren't good. You might even have the version where one outlet is blocked? From a power-improvement standpoint, stock mufflers on an L98 create a bigger restriction than their cats. This is generally true for stock C4 mufflers versus any of the cats used by the factory. It's why I included them as a good component choice when building a performance exhaust. They improve exhaust smell and quiet w/o INDUCING drone -- like most oval/box mufflers seem to do.

That said, it's probably difficult/impossible for most owners/drivers to actually FEEL the difference with any muffler/cat swap made during a trip to the muffler shop. Sound quality is likely to be the more satisfying result.

As for sound-wave cancellation, my IMPRESSION of how this happens (since it wasn't addressed), can be seen via a cross-section of something like a Flowmaster. A center partition splits the exhaust against the outer sides. Essentially half goes either direction and is bounced about 45-deg off axis. The "wave cancellation" comes when each half is rerouted back at each other before entering the muffler outlet. When considering the success of this approach, I look at the sound quality and member-complaints. This seems to be missing from Mark's PPT.

Designing a muffler would be something fun to do. I haven't seen much in the way of chambers that's been used to enhance the average home speaker system other than Bose. (But, I'm behind the times if it's been leveraged in 21st century products! LOL) I will say it's interesting to look at the maze of a Bose speaker and consider Tom's remarks about the bends in a system....or their validity in this conversation. It's been years since I actually heard a WAVE radio. I wish I could hear one again. I'd listen to see if it was essentially a port-loaded bass speaker with higher-base frequencies removed.

That's kind of a crude way to describe what I think people should shoot for when building their exhaust. Plus, it combines what Tom and I have said to make possible sense.

If one could DO it, I'd be curious to know what happened if we could jam a 3-4 cu/ft box under the car (which is impossible). The exhaust pipe would be your port...and the SIZE of the box would fulfill Vizzard's representation of a "terminator box". Plus, the box ITSELF would be tuned much lower than a "tiny" muffler. I bet it would sound GREAT! LOL

I wonder if we can get those Bose guys to design exhausts?! LOL

 

Except the missing piece in your analysis here is that both "sides" of the split exhaust are in the same phase, so there is zero cancellation of anything. Unfortunately, unlike a speaker cone where there is a front wave and a back wave exactly 180* out of phase with each other (i.e., positive and negative pressure waves of equal magnitude), there's no simple way to get such a split in an exhaust pipe. You never have a negative-pressure out-of-phase part of the pulse wave to tap.

You might have at least some negative pressure in a primary tube, but even there that doesn't seem to work as noise cancellation. Evidence for that is that an even-fire engine like an inline 4-cylinder, inline-6, flat-crank V8, or V12 should all have ideal cancellation at their collectors, and yet they can be very loud. So even in the primary tubes the positive pressure is probably much stronger than the negative pressure in between valve openings.

Flowmasters are actually pretty terrible mufflers, btw. For the (usually minimal) sound attenuation they provide, they have a lot of restriction. The whole idea of putting a wall in the way of the exhaust, splitting it, and then ramming the two halves back into each seems to create a lot of back-pressure.

 

Either buy Cora’s or fab this....

https://www.corvetteforum.com/forums...ing-corsa.html

 

That was basically my point. I don't see how cancellation of anything is improving, explaining, or supporting the PPT being presented. I basically took a dumb-azz stab at getting someone to point out how it's being accomplished...since I don't get it or see that it works. LOL

In a bass box, you don't want sound bouncing back into itself. It'd think the same would be true with muffler sound abatement (tuning?)

 

Looks like an interesting read...and set of formulas. I don't think I've ever seen someone post the mathematics necessary to design/construct the correct length (helmholtz?) resonator for sound-wave cancelling.

I've never quite figured out how a tube -- that's plugged on one end, seemingly keeping air from moving -- could allow sound/pressure waves to form/cancel others in the "main pathway".

 

Yeah, since there's really no negative-pressure phase in the exhaust pipe, there can't be cancellation within it.

This would have been my next post if SurfnSun hadn't beaten me to it. A quarter wave resonator is the way to accomplish the cancellation. It doesn't need flow - it just needs the pressure wave to go down it and then bounce back. In fact, an opening at the end would reduce its effectiveness quite a bit. If that wave is timed properly, it will hit the main exhaust pipe out of phase with the main pressure pulse at the rpm of the resonance, and cancel a lot of it out.

 

OK...I'll bite. I thought the "space" between exhaust pulses were a type of negative-pressure phase (wave). It's one of the 3 things that contribute to reversion. Maybe my terminology/impression is wrong on that?

During space movies, they always play the sound of spaceships zooming around. I'm assuming that's fake because sound can't travel in a vacuum....Of course, I've never "googled" how thrust works in it either.

In a helmholtz resonator, I guess the sound can travel through the atoms of the "stagnant" air even if the air doesn't move per se? Of course, I understand that it wouldn't work if the end of the resonance tube were opened! Too bad I don't remember more about physics. LOL

(I never learned a ton about sound waves moving through space/air....Just speaker building and theory).

The Helmholtz principle seems leveraged in Side Effects sidepipes (if you've seen the pic of mine in this thread). As the exhaust is routed around...and back into to the aluminum canisters (at the front of the side tubes), sound is supposed to enter and return "smoothed"....like blowing into a coke bottle. Sounds like it's own version of a helmholtz. Maybe they knew what they were doing.

 

This is a slightly educated guess on my part, but I believe the main exhaust pipe(s) just sees fluctuations between high and low pressures, but never negative pressure. This is for a couple reasons: on a V8 there are four or eight pulses for every two crank rotations (not just one like in a primary); and because the velocities in a properly sized exhaust system are pretty low (again, much different than in a primary pipe).

Bit of a tangent, but yes soundwaves must travel through some kind of material or they can't exist. Outside of the spaceship it is silent. Inside occupants can still hear engine noises as it vibrates through the structure and the cabin air they breathe (assuming the cabin is pressurized).

The air can vibrate back and forth without flowing. So in a closed pipe it moves back and forth the same amount. You certainly can still have resonant waves in an open-ended tube where air is flowing through it: like the primary pipes or like any brass or woodwind instrument. So you can get the Helmholz resonance whether it's open or closed. What you CAN'T get if it's completely open is the reversion. If there is no wall at the end for the wave to bounce off of, then you can't get the pressure wave to bounce back and hit at the entry into the pipe.

Reversion can still work with an opening at the end and resultant flow, but it won't work if it's just a straight pipe with an outlet as big as the inlet - there would be no "wall" to reflect off of. But if you look at a tuned-pipe for a two-stroke engine, you see the reversion principal at play even with gas flow through the pipe. They have two basic designs: 1) the pipe tapers to a much larger diameter downstream and terminates in a "wall" with a small exit opening in the center of the wall, or 2) the pipe tapers to a large diameter and then back down to a small diameter exit opening. In both cases, the wall or reverse taper sections provide the surface for the pressure waves to bounce off of, and the small opening at the end allows the exhaust gas to still flow out. In the case of a quarter-wave resonator for squashing a drone, we just don't need the flow since the regular pipe already has plenty of flow (or at least it should!). An opening at the end of the resonator would be overly complicated and would also introduce an unmuffled exit point for exhaust gas, creating other noise problems. So we keep it closed and don't use it to allow flow - we only want to use the wave reversion for cancellation.

It would take more detailed examination to know for sure. Based on what I think I see, it's possible but unlikely that Helmholtz effects are playing a role here. Or, maybe they are but it's not pure. The problem I predict is that the aluminum canisters look too short to work as a quarter-wave reflector at anything below redline rpm. So I doubt they can cancel any waves at their entry point. However, it's possible that some reversion cancellation can happen all the way back to entry of the system, where it attaches to the Y-pipe and then splits into two. That might be too long to work at the typical drone rpms (usually 1700-2000rpm or so), but maybe not. Or maybe for this system's lengths and sizing, the drone is lower and this is the perfect length.

My guess, though, is that the canisters act more like an accumulator/buffer, an expansion tank. That would allow the pulses to dissipate a bit by expanding before going down the exit sidepipes. In this case, it won't cancel any particular frequency, but it will quiet everything somewhat by reducing the magnitude of the pulses at all frequencies. This operates basically like a resonator ahead of a muffler (I think I'm seeing cherry-bomb style mufflers in the sidepipes just before the exits?)

 

4.11 gears in the differential. Now I'm always above drone rpm, and the performance gains!

 

Yeah, sure...if you want to take the easy way out!

Seriously though, this is actually a good point.

 

I didn't see anything more than with 3.73 so it probably was slight enough to not notice. I did see my fuel gauge needle drop faster though.

 

I wonder if closing off one side of a dual outlet muffler would create some cancelation?

 

That would be way too short of a length to work as a quarter-wave resonator at the rpm of the typical drone problem. However, that is apparently sort of what Corsa does. Maybe theirs functions as a eight-wave resonator? I don't know.

 

BTW, does anyone have a good picture of the inside of a Corsa C4 muffler? I'm not sure all the newer ones they have pics of are representative of the C4 version.

Looking around a bit more, I see their general concept here:



And this is what it looks like in a single-outlet muffler:



I still haven't seen a cutaway diagram or picture of the single-in/dual-out Corsas that we have for the C4 application. But we can assume it uses this same idea of a folded chamber, and we know that one of the two outlets is plugged. So this will definitely work as a quarter-wave resonator, since they can make it long enough by folding it back on itself a few times. The restrictions don't really matter, since this is just routing sound waves and not actual flow. The actual flow is straight through.

It's funny, because these were on my car when I bought it, and I've never really looked into them too much. I just knew they were supposed to be good. This is pretty cool! I bet my car with most regular mufflers would have an ear-bleeding drone. As it is, the drone is not too bad. A full-sized quarter-wave resonator made of 3" tubing would probably cancel even more drone, just by having more "power" or magnitude to its resonance.

I currently have a normal 3" X-pipe in the system. It would be interesting to try the 3" Walker Ultraflow Welded X muffler in its place. It should still flow similarly well to the plain X-pipe since it is straight-through, but with the glass packing and perforations it should make everything quieter. I know my neighbors would like that! Anybody ever tried this? Better yet, can anybody point to a flow or dyno comparison between this and a plain X-pipe?

 

That piece appears to be the same design as the Magnaflow part I recommended. With the exception of the crossflow interaction, Vizzard has a formula to accurately predict flow of any size pipe. Beyond that, I wouldn't think the difference would be "bad"....since both are the same thing (though one has a box built around it). More importantly, if claims of 2000cfm are accurate, that more than enough to support your build.

I suppose you could get into the issue of perforation -- which reminds me of the comparison of a smooth vs turbulent intake tube! I'm going back to the 2000cfm though! I can't speak to THIS manufacturer's version but I do really like Magnaflow's counterpart (in terms of sound quality).

FWIW, I remember a thread several years ago where someone cut into the MF unit. It MIGHT be they posted/complained because the inner "X" was a size smaller than the inlets/outlets? IOW...2.25 vs 2.5 or 2.5 vs 3" maybe? Anyway, they felt cheated IIRC. I think I suggested it might be a design feature to accelerate air "across" the opposing pipe. I'm not sure if it would be possible to troll it up anymore...Maybe search for Magnaflow in the title? But, that would return TONS of threads.


(As for my side pipes, the area you think is a muffler is merely heat-shielding to avoid paint blistering the rockers. Those alum canisters are built like resonators. When I bought them, the packing was falling out. I bought 2k-deg cement, stainless screen, and used new batting to re-line those "sound chambers"....which are the only sound abatement for the system.)

 

PERFECT!

 

Interesting thread ... looked thru my saved muffler images and found this one.
Might be the Vette Corsa ... think I saved it from this forum?