Landseer

What about Magnaflow same-side offset, like in the picture way above?

ptuomov

Depends on which muffler it is. Do you have the name or the part number?

My impression is that across brands, XL's usually have baffles, turbos have a Z-path, and then sport mufflers are straight thru. But that's just impression.

Ramona

Unfortunately if your trying to get rid of low frequency noise this means a baffle/chamber type of muffler. Adding more straight through mufflers is just reducing more high frequency noise.
Have a look at the mufflers the factory is fitting to performance Ford/GMH vehicles. These are quiet. Aftermarket kits for these vehicles don't always add much in the way of horsepower, just more noise. I remember reading an article in one of the enthusiast magazine where the best they could achieve with a comparison test was 2hp. The car sounded better though. Check out the prices on eBay for these new style mufflers, if your expected to pay $800 to $900 for a muffler in SS I want to know what's inside!

ptuomov

I agree that factory exhausts are nowadays really good for high-performance cars. The car factory engineers are not hacks and they have the computing budget to get the exhaust exactly right given their objectives. A hobbyist is going to have a hard time coming up with something better.

Some mitigating factors, though:
- I have a different objective function, I care more about power and less about sound than the factory engineer
- The car is quarter century old
- The performance mods are such that the exhaust has to be completely different from stock anyway
- This is a turbo car, so the pulse tuning objective for the turbo-back exhaust can be ignored and focus can be on sound and back pressure only

Baffles reduce sound pressure pretty much across the board, I think. As far as specifically muffling low frequencies goes, I think it's not so much baffles but simply the size of the muffler. It is easy to muffle low frequencies with a large muffler and nearly impossible with a small muffler. I think that's just the nature of the beast.

Because the muffler size is limited, I am thinking a bit more about pipe resonance. At minimum, I should be able to eliminate the drone caused by pipe resonance.

Landseer

Part number for 2 1/4 mids, # 14375
They're all sport with magnaflow.
My sameside offsets are straight through.
http://www.magnaflow.com/02product/02muffler.asp

Ramona

During my "searches" I came across a forum that had test results for all the major performance mufflers. Interestingly the hp difference was only about 3 hp across the lot. The volume of noise however varied a lot.

Tried to purchase a Magnaflow xl but the postage was going to be $162. Instead have sourced a Hooker aerochamber locally for $102 including postage. This is basically a straight through with a chamber and a section of absorption material. So basically its going to be a 3" system with aerochamber, Edlebrocke, Magnaflow. Still a straight through but each muffler has a different perforated style of tube plus a chamber. Don't really have a drone now but this set up should avoid it.

Landseer

The way I bought the magnafows here in the states was by special order placement at Pep Boys.

Shipping to the store was free.

ptuomov

Ok, so I did some wave computations and the HQ resonator is not going to be the answer to the low-frequency pulses. Ignoring the gas mean flow and assuming that SOS in hot exhaust gas is 1400 ft/s, 1.5 ft difference in pipe lengths would cancel the pulses at 7000 rpm. That's really not that helpful. I don't mind if car screams at 7000 rpm, I just want it to be reasonably quiet at say 1700 rpm. The 1.5 ft length difference between pipes is not going to have any impact (<5%) on engine firing frequency noise at 1700 rpm. This idea is another dead end, at least for my purposes. It might help racers looking to pass track noise limits at high rpms, though.

tveltman

Tuomo, check your PMs

tveltman

Mmm, just sent it, check again...

Didnt realize you were actually online

Ramona

Hooker Aero chamber muffler arrived. Very impressive looking design and excellent build quality, then I noticed its made in China.

PorKen

Tuomo - do you have a photo of your current exhaust system?

I have found that installing balance pipes wherever possible will put the tone in a more pleasant range.

Even when changed to 'GT' resonators, this setup was not that loud at low throttle angles, and sounded like a V10 at full throttle.

ptuomov

Here's the current system:





It's completely divorced 3" dual system without any cross-over, with Borla xr-1 mufflers sized like stripper's thong. So it's not exactly a surprise that it's loud.

The next iteration will definitely have a cross-over. Most likely merging the flow into a single oval pipe after the cats and then divorcing them to the mufflers and merging them again into a 4" tail pipe (or muffler). I am trying to work out the pipe lengths in a way that the sections don't resonate at same frequencies.

A separate question: I took half-assed measurements of the S4 exhaust heat shield. Especially the angles are suspect. Anyone got better measurements?

hernanca

I have heard of folks using a T'd off dead-end length of exhaust tubing, sized in length (IIRC) to 1/4 wavelength of the undesired frequency, as an alternative to a BAM.

It serves to reflect a wave back to cancel the undesired tone.

I don't know what length of (dead end) pipe that works out to, or where it would fit under our cars. It may be possible (from what I've read in acoustics) that you could do a combination of a shorter length of pipe with a large-ish end chamber at the dead end, to give the same effect - volume of the end chamber would have to be equivalent to that of the length of dead-end pipe you were not able to extend out. Kind of like a large Helmholtz resonator, but used to cancel a sound. I have not heard of anyone doing the latter, however.

Of course, we have to know what tone we want to cancel.

When I looked into it, I concluded that drone comes from the lub-a-dub of our uneven firing order finding it's way through the system and rearing it's ugly head at some component's natural frequency. That lub-a-dub occurs every 720 degrees for our 90 degree crank plane V8, and works out to about 40 Hz (about the lowest sound we can hear) at about the usual RPM's folks complain about drone (1700-2600 RPM). (Though I don't remember if I recalculated everything after learning how temperature affects the speed of sound!).

I believe that merging the two sides of your system at a point where they have had equal length thus far, is key to minimizing any potential drone.

Other things to consider are mount points (are you dampening an antinode?), consistency of material sizes, thickness of material, mandrel bends (or not), quality of products used, lengths of pipes. I believe all these can affect the tone by bringing in timbre effects and bringing out (or dampening) natural frequencies.

I disagree that adding similar design resonators in series will ever start to increase noise level, but I don't know that from experience. However, I have also considered having different resonator designs (that is, from different manufacturers) in series, as a possible way of achieving a "richer" exhaust tone.

FWIW, my exploration of exhaust tone started after constant awakenings from a 4:00 am newspaper delivery via a 90's+ Camaro with the sweetest musical exhaust sound I had ever heard, and I have never heard anything like it since. My quest continues...!

928mac

Holy F&^% that is a sweet shinny set of exit pipes