I came across this MRT-Direct.com muffler for the new Ford Focus ST while cruising through the mag and my brain screeched to a halt!
Not a lot to it! Is it basically a straight exhaust with a tuned length chamber on the end to reduce a certain sound range? If so is the only reason volume is acceptable because of the muffling effect of the factory turbo and Cats?
MrJoshua wrote: Not a lot to it! Is it basically a straight exhaust with a tuned length chamber on the end to reduce a certain sound range? If so is the only reason volume is acceptable because of the muffling effect of the factory turbo and Cats?
Basically. That's how the Abarth "muffler" works as well. Just cats and turbo.
JThw8 wrote:MrJoshua wrote: Not a lot to it! Is it basically a straight exhaust with a tuned length chamber on the end to reduce a certain sound range? If so is the only reason volume is acceptable because of the muffling effect of the factory turbo and Cats?Basically. That's how the Abarth "muffler" works as well. Just cats and turbo.
same as the neon SRT-4. a turbo counts as a muffler, so it is all legal.
Basically yes - the end cap bounces the sound back towards the outlets to cancel out certain resonate frequencies.
Zoom in and you'll also see it's just two outlets butt welded to the side of the pipe. The sound waves pretty much merrily continue down to the end of the pipe, then bounce back. They've no real reason to come out sideways. Vaguely akin to turning your headphones sideways to your ears.
They'll also probably flow pretty poorly. The design requires the exhaust gasses to make a sharp 90 degree turn to go out the side of the pipe. Not something gas flows want to to. It creates quite a bit of turbulance and drag.
It's a helmholtz chamber.
http://en.wikipedia.org/wiki/Helmholtz_resonance
so this likely wouldn't work that nicely on a naturally aspirated or supercharged car as far as limiting noise goes? unless you put a perforated core/packed core muffler upstream of it, which sort of gets rid of the weight benefits of what's essentially the simplest "muffler" setup I can think of, short of a set of baffles shoved up the end of a section of exhaust tubing
It'll probably reduce some drone.
It can reduce noise, snd flow. Simplest is the dimple pipe. Veru effective if done right.
I'm glad I wasn't the only one scratching my head over that one...
I personally like the Lamborghini looking exhaust tip on the ST.
Isn't that the same kind of thing they do on factory intake tubes to reduce noise and drone?
foxtrapper wrote: They'll also probably flow pretty poorly. The design requires the exhaust gasses to make a sharp 90 degree turn to go out the side of the pipe. Not something gas flows want to to. It creates quite a bit of turbulance and drag.
Not so much as you'd notice. The end of the exhaust system is where the exhaust is coolest and therefore slowest.
Experimenting on an RX-7, I found that a simple 1 7/8" reducer hammered backwards into the 2.5" tailpipe reduced noise and drone at least as much as adding an additional muffler, and it made no difference in power output as measured by air/fuel ratio changes (open loop speed density EFI) and by quarter mile trap speeds. The rest of the exhaust was 2.5" pipe and a couple perforated core glass pack mufflers.
Made the same thing myself, after making a similar observation. Just a wee flange around the tailpipe cuts the cracking tremendously.
That is not the same thing as plugging the end of a pipe completely and drilling a hole in the side of the pipe for the gasses to come out of though.
And on an intake, the flow is reversed. Makes an appreciable difference to how the system works.
This strikes me as interesting.
Knurled wrote:foxtrapper wrote: They'll also probably flow pretty poorly. The design requires the exhaust gasses to make a sharp 90 degree turn to go out the side of the pipe. Not something gas flows want to to. It creates quite a bit of turbulance and drag.Not so much as you'd notice. The end of the exhaust system is where the exhaust is coolest and therefore slowest. Experimenting on an RX-7, I found that a simple 1 7/8" reducer hammered backwards into the 2.5" tailpipe reduced noise and drone at least as much as adding an additional muffler, and it made no difference in power output as measured by air/fuel ratio changes (open loop speed density EFI) and by quarter mile trap speeds. The rest of the exhaust was 2.5" pipe and a couple perforated core glass pack mufflers.
this is very relevant to my interests, as supercharged Minis are rather difficult to keep quiet, especially once one swaps out the stock manifold for a header. I mean obviously they aren't as noisy as a rotary, but still. what you added just amounted to a ~2.5"-to-1.875" reducer, installed small-end-first into the tailpipe? do you think something similar could be worked into this setup, upstream of the tailpipes, or would it just be wasted material at that point? I'm thinking of ways to free up the exhaust system in my Mini without making it too obnoxiously loud, and I would imagine I could do the same thing on my Miata for a really lightweight (but not obnoxious) exhaust.
Spinout007 wrote: I'm glad I wasn't the only one scratching my head over that one...
I was even more confused when I first saw the picture because it looked like it was actually a complete loop!
Spoolpigeon wrote: Isn't that the same kind of thing they do on factory intake tubes to reduce noise and drone?
Yes. Helmholtz resonance.
If you don't have Facebook access, below is a picture of a SpinTech muffles used as a resonance chamber on a VW R32. It is mounted perpendicular to the exhaust pipe with the inlet and outlet of the muffler welded to the pipe. Apparently cut the exhaust noise in half with no power loss (aside from the added weight of the muffler.
http://www.facebook.com/RacetechMotorsports/posts/10151409989799086:0
Now THAT is interesting.
http://kalecoauto.com/index.php?main_page=product_info&cPath=11&products_id=41&zenid=a6vojnlr5lv2rgv5mja8amke27
Slyp_Dawg wrote: this is very relevant to my interests, as supercharged Minis are rather difficult to keep quiet, especially once one swaps out the stock manifold for a header. I mean obviously they aren't as noisy as a rotary, but still. what you added just amounted to a ~2.5"-to-1.875" reducer, installed small-end-first into the tailpipe? do you think something similar could be worked into this setup, upstream of the tailpipes, or would it just be wasted material at that point? I'm thinking of ways to free up the exhaust system in my Mini without making it too obnoxiously loud, and I would imagine I could do the same thing on my Miata for a really lightweight (but not obnoxious) exhaust.
Agreed. It's pretty easy to make a R53 rather obnoxious. My g/f's car has a factory JCW cat-back with a center straight pipe (resonator eliminator) and it's border-line too much (since she's always inside the car, she doesn't really know how loud it is). One friend has a Borla Race and it's almost unbareable at times. I installed a OBX header, high-flow cat and Invidia exhaust on another friend's MCS and it was unbareable. We had to reinstall the OE header to sell the car.
There was a thread (I think) on NAM about a guy who did a battery-delete and installed a R56-style system. He experimented with a bunch of side take-off resonator Helmholtz pipes before he found one that toned it down well enough so the car wouldn't set off car alarms as he passed by.
Just spitballing ideas, but would replacing the factory midpipe/resonator with a 2.25-2.5" ID, ~4" OD perforated tube, packed core resonator that ran the entire length of the midpipe (flange-to-flange, allowing an inch or so at each end for hardware/fasteners), feeding into a dual-pass perforated tube packed-core muffler (think two packed-core mufflers beside each other, connected by a 180deg elbow, all stuffed into an oval case that looks vaguely like a big Flowmaster muffler and thats basically it), then using this funky hemholz-resonance muffler idea for the tailpipe, perhaps with the reducer idea Knurled used mounted somewhere upstream of the tailpipes but downstream of the final muffler? I feel like for the standard exhaust manifold, this setup would be more than sufficient, and might be sufficient for an aftermarket header as well, depending on the density of the packing and the volume of the resonator and muffler... It sounds complicated, but that may just be my ahem thorough idea-presenting abilities...
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