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Custom Exhaust Questions
https://slantsix.org/forum/viewtopic.php?t=46012		 Page 2 of 3
Author:  olafla [ Wed Aug 24, 2011 12:57 pm ]
Post subject: 
[quote="SlantSixDan""]
Testimonials involving cars that don't have slant-6 engines (or at least some kind of inline-6) are not really relevant; inline-6s have particular exhaust noise characteristics that are more difficult to silence than other kinds of engines. Also, every Subaru Impreza ever made has a catalytic converter, which itself substantially quiets the exhaust before it even gets to the muffler, making that testimonial even less relevant to the Dart in question.[/quote]

Apart from working in a muffler shop, according to his profile, zedpapa has a 1970 dodge dart w/225 /6 bored .040" over, holley 390cfm w/vac. sec., compcams 252s, clifford shorty headers w/2.5" exhaust w/flowmaster, f-body 11" front discs, aluminum A-833OD, 8 1/4 w/3.21 SG.
Quote:
...but I also doubt it's the slightest bit true unless the Flowmaster people have figured out a way to sidestep the laws of physics.
.

It is my understanding that they make use of the laws of physics applied to flow in gaseous matters known as the kinetic theory of gases.

Scavenging is enhanced by good design headers, often using resonance tuning. Scavenging mufflers don't give you any power, but properly installed may overcome some restrictions in a stock exhaust system by letting you have a little better flow.

I totally agree in the fact that the exhaust flow in six-cylinder engines are different from V8s, but there are no header/muffler dyno tests available for SL6 engine as far as I know. The dyno tests available for V8s, like the one linked to below, are usually done by simply mounting different mufflers on the same pipes, usually without consulting the muffler designers about optimal pipe size/placement or other details for their product, and therefore relatively uninteresting in a scientific setting, but they may indicate a bad/good replacement muffler for an otherwise original exhaust system.

mustang50magazine_testing_15_mufflers

Olaf.
Author:  SlantSixDan [ Wed Aug 24, 2011 1:12 pm ]
Post subject: 
Quote:
It is my understanding that they make use of the laws of physics applied to flow in gaseous matters known as the kinetic theory of gases.
That's the claim. I'm sure it sells mufflers. I'm not sure it's true.
Quote:
Scavenging is enhanced by good design headers, often using resonance tuning.
Yes.
Quote:
Scavenging mufflers don't give you any power
So we have this phenomenon known as scavenging. We agree properly-designed pipework, especially headers, makes it happen. The notion that there's really any such thing as a "scavenging muffler" is open to debate, but for the moment let's assume there is. You are now asserting that scavenging that happens by dint of a muffler doesn't give you any power -- unlike scavenging by dint of headers, which does. Please explain.
Quote:
but properly installed may overcome some restrictions in a stock exhaust system by letting you have a little better flow.
[citation needed]
Quote:
I totally agree in the fact that the exhaust flow in six-cylinder engines are different from V8s, but there are no header/muffler dyno tests available for SL6 engine as far as I know.
Which means all we're all doing is guessing.
Author:  olafla [ Wed Aug 24, 2011 1:59 pm ]
Post subject: 
Scavenging by tuned headers may give more power than open exhaust, adding a muffler to an exhaust system usually makes another restriction in the system. Adding a scavenging muffler may overcome some of the restriction caused by a normal muffler, thus not 'giving' more power, but preventing additional powerloss caused by the restriction from adding a muffler in an exhaust system.
Quote:
[citation needed]
You may cite me.

Olaf.
Author:  SlantSixDan [ Wed Aug 24, 2011 2:07 pm ]
Post subject: 
Quote:
You may cite me.
Er…no, "citation" implies reliable, properly-supported assertions based in facts and science, not guessing and handwaving and repetition of marketeering claims.
Author:  olafla [ Wed Aug 24, 2011 2:11 pm ]
Post subject: 
Your opinion on that is irrelevant.

Olaf.
Author:  Joshie225 [ Wed Aug 24, 2011 2:21 pm ]
Post subject: 
Replacing a restrictive muffler with a less restrictive one absolutely can make for improved engine performance. It has been shown that Flowmaster mufflers are not necessarily the lowest backpressure muffler available.

Flowmaster mufflers have an interesting property in that they acoustically divide the exhaust system. This can lead to an increase in power along even with a slight increase in backpressure. This is also why vehicles with such mufflers can have resonance problems. The Flowmaster muffler create an acoustically shorter tail pipe.

Dart270 has reported on dyno tests performed by Cameron Tilley. The Hooker Aerochamber muffler performed best, but they are relatively loud. http://www.slantsix.org/forum/viewtopic ... mber#85577
Author:  olafla [ Wed Aug 24, 2011 2:42 pm ]
Post subject: 
The noise and specifically the drone poblem was also mentioned n zedpapa's post:
Quote:
...the secret to making a FM work is to put a tailpipe that is at least 18" long and to use one size smaller pipe for the tailpipe. for example, if you have a 2.5" pipe from the header/manifold, run a 2.25" tailpipe to the bumper. the resonation and the drone will not happen
.

If this recipe works equally well on all engines, I don't know, but I believe the principle is sound in SL6 exhaust systems in general.

Olaf.
Author:  raPoM [ Wed Aug 24, 2011 2:53 pm ]
Post subject: 
Just so you guys know- zzedpapa shop(where he works anyway) lyons auto in San Marcos Ca built my 67's exhaust that I had the 40's series muffler. They built it exactly as he stated,and I still had drone.
Author:  olafla [ Wed Aug 24, 2011 4:06 pm ]
Post subject: 
Haha, always good to remember that theory and practice don't always agree! Nothing beats practical experience!

Can you please tell us the data of your engine/exhaust system, and at what engine speeds does the drone become an issue, and whether it dissappear again at higher speeds?

Olaf.
Author:  raPoM [ Wed Aug 24, 2011 4:43 pm ]
Post subject: 
It was a 67 Dart 2 door, 225 904. Stock bottom end,big valve head(engnbuilder valves) old clifford long tube headers. Dual 2 1/4 head pipes brought into a custom y pipe to 2 1/2 singe,flowmaster 40 with a 2 1/4 tail pipe. Drone would start around 2800 rpm and go away at 33-3400 rpm. It had a killer sound,but did get loud on the highway,and the drone was annoying. If I were to do it over,I would go with either a flowmaster 50 and a resonator,or a dynomax hemi (turbo style) muffler.
Author:  Jeb [ Thu Aug 25, 2011 5:32 am ]
Post subject: 
I had a flowmaster 40 on my 74 Duster, 225, super six, 2 1/4 exhaust all the way back. It definitely made it's presence known, especially when I started it up at the gas station. The interior noise wasn't bad unless you drove around turning 3500 RPM all the time.

On the other hand, I have a Thrush turbo ($16 muffler) on my D150, and it's QUIETER than the factory muffler!
Author:  bmweater [ Thu Aug 25, 2011 2:21 pm ]
Post subject: 
I have a Flowmaster Delta Flow 40 series on my 64 slant with a cam, headers, intake work, 2bl webber. Its a 2.5" all the way out, its sounds great at idle has a great lope most people think its a v8...but at higher RPMS like 3k it drones like crazy. As such I am going to switch it up to a Magnaflow...heard a clip on youtube and i think it will make a killer sound and still me discrete.
Author:  SlantSixDan [ Thu Aug 25, 2011 2:31 pm ]
Post subject: 
Quote:
I am going to switch it up to a Magnaflow...heard a clip on youtube and i think it will make a killer sound and still me discrete.
I remain leery of those Magnaflow mufflers. I really wanted to like them, so much I tried 'em several times on a couple cars, one of which was a slant-6. Every time it was the same: they started out quiet enough and sounding good, but gradually grew louder and on the slant-6 Lancer there was an obnoxious drone between 58 and 68 mph that would not go away no matter what I did with tailpipe diameters, resonators, etc. I finally gave up on 'em and went back to large-flow stock-type mufflers (i.e., a muffler designed for a bigger engine than the car has).

Just like a pipe organ, different lengths and diameters of pipe will resonate at (and amplify) particular frequencies. And this is why a muffler that's almost stock-quiet on one car with a given engine may make objectionable noise on another car, similar but not identical, with the same kind of engine. Stock-type mufflers (baffles/chambers etc.) are much, much less sensitive to placement.
Author:  Aggressive Ted [ Thu Aug 25, 2011 3:21 pm ]
Post subject: 
Well said Dan. My MagnaFlow was fine for about two years then it developed quite a drone and my power dropped off. I thought the mice got in there and built a home and plugged it up!

After replacing it we checked it out. Looking down the pipe it visually looked fine except for a nasty jagged crimp at a bend of the perforated pipe.. Not sure what happened to it......it was a 22" long body.
Author:  Aluminum Six [ Thu Aug 25, 2011 3:21 pm ]
Post subject:  Tailpipe scavenging
In all my experience the long flow hedders with a h pipe balancer and low restriction turbo muffeler works best.

And I have a lot of inline engines.

Inline 8's have the charichteristics as inline sixes, but with the harmonics of 8 cylinders, you have a different sound, with split hedders, like a raunchy v8 or a harmonious symphony of chainsaws.
Due mostly to the Siamese head porting and the oversquare design of an inline motor, where the stroke is longer than the bore.

One of the $#!+ sounding motors ive ran off the factory exhaust is a 1946 Lincoln flathead V-12. Deep burble but whine and resonation from 300 rpm to 1600. They have 6 power strokes per revolution therefore a really low idle speed. Am slowly porting the block for flow but the sound will never change, just get louder.

If you really want to scavenge at the muffler there's an outfit on the wear coast for big money will replace your muffler with a turbocharger, multiple times, and claim very little noise just a performance rumble.

Or you could run rich and invent the 2.25 inlet turbine... Like a cross between a GE turbine and a 30" glasspack. Guys used to screw spark plugs or something into their tail pipes in the 50's to shoot flames out. Similar to that but safe for someone walking behind your vehicle.
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