Quietest Catless Header

[mav1178]

Originally Posted by Irace86.2.0

A sentence that is also a paragraph stands on its own as a statement void of qualifiers.

What you just qualified is a different statement than saying the number of cats doesn’t mean anything with regard to noise. Someone could conclude from that solo statement that a catless header could be quieter than a catted header when (for all reasonable situations) would never be the case.

You could have said, the number of catalytic converters effects the noise, but other exhaust components can do just the same without impending performance or something, and that would be fine.

I should also say, that your video doesn't corroborate your statement well. The video says the vehicle made 85lb at 10' away. That is all well and good, but that isn't the SAE standard for performing an exhaust test. The rough standard is to measure the exhaust note 20'' from the tail pipe at a 45 degree angle.

If the decibel reading at 45 degrees at 10' is 85 then we could predict what it would be at 20'' (1.67'), where I-2 is 85 dB, d-1 is 1.66'', d-2 is (10'-1.67') 8.33', and the decibel reading would be 99, which would fail in California.

http://hyperphysics.phy-astr.gsu.edu...c/isprob2.html

https://govt.westlaw.com/calregs/Doc...efault)&bhcp=1

and you're also adding some assumptions about 45 degree angles.

The videos I made were just 10' directly behind the left side tailpipe, no angles. Because at that time I had no easy access to empty parking lots with no walls within 50', I could not replicate the SAE exhaust test in California.

The video is accurate for comparison to other exhausts tested under the exact same condition and location, but beyond that it's useless for comparing against your video vs some other person's video of random exhaust test and drive-by.

As for what I said, the number of catalytic converters is not the issue and that's exactly what I said. Most people equate catalytic converters as the same thing, when in reality OEM cats vs aftermarket cats need to be differentiated. I could have worded it in great detail but the question as asked by OP is regarding the number of cats (or lack of).

We can nitpick what I said but the main point I'm getting at is that whether an exhaust has a catalytic converter (or not) is not a primary determination of noise suppression, it's the type of catalytic converter (or volume of sound suppression items in the entire system)

[Irace86.2.0]

Originally Posted by mav1178

and you're also adding some assumptions about 45 degree angles.

The videos I made were just 10' directly behind the left side tailpipe, no angles. Because at that time I had no easy access to empty parking lots with no walls within 50', I could not replicate the SAE exhaust test in California.

The video is accurate for comparison to other exhausts tested under the exact same condition and location, but beyond that it's useless for comparing against your video vs some other person's video of random exhaust test and drive-by.

As for what I said, the number of catalytic converters is not the issue and that's exactly what I said. Most people equate catalytic converters as the same thing, when in reality OEM cats vs aftermarket cats need to be differentiated. I could have worded it in great detail but the question as asked by OP is regarding the number of cats (or lack of).

We can nitpick what I said but the main point I'm getting at is that whether an exhaust has a catalytic converter (or not) is not a primary determination of noise suppression, it's the type of catalytic converter (or volume of sound suppression items in the entire system)

The video shows someone standing at an angle to the rear. Is it 45 degrees? I don’t know, but it is close enough, whereas, 10’ is not anywhere close to 20” Regardless, the decibels are still over the limit, which is my point.

I got your point, but that sentence/paragraph was just factually incorrect, so I thought I would make a point of getting those qualifiers stated more clearly, less someone naive reading that from a vendor run with the idea that removing a cat will not impact sound. Thanks for clarifying your point for the record.

[Contender]

Originally Posted by x808drifter

The stock one de-catted.

Plus 2

[Irace86.2.0]

I know many people have decatted the header and several others have straight piped the header. Not everyone has access to a welder or has the skill set, but I wonder if anyone has created a resonator out of the cat. It seems to me like it would be easy to cut the cat in half, remove the cat, weld in a perforated pipe (buy a pipe and drill holes or buy a perforated pipe), place some packing in the space, wedge the pipe into the other end then weld it in place and weld the center back together. This would create a stealth straight pipe with reduced noise because of the resonator.




Thoughts?

[weederr33]

Originally Posted by Irace86.2.0

I know many people have decatted the header and several others have straight piped the header. Not everyone has access to a welder or has the skill set, but I wonder if anyone has created a resonator out of the cat. It seems to me like it would be easy to cut the cat in half, remove the cat, weld in a perforated pipe (buy a pipe and drill holes or buy a perforated pipe), place some packing in the space, wedge the pipe into the other end then weld it in place and weld the center back together. This would create a stealth straight pipe with reduced noise because of the resonator.




Thoughts?

Sounds kinda pointless unless you live in a place that is strict on mods.

[churchx]

And pictured seems more of muffler, not resonator.
Resonator acts more by it's size/volume, to cancel out specific frequencies by, well, resonating effect, which is specific to it's size, not by muffling overall noise level by reducing exhaust gases energy, like mufflers do, by different design restrictions to exhaust path (be it walls to redirect several times exhaust path within muffler, or packing material).
And given resonator effects depending on it's size (have no info at hands on accoustic releations) i have suspicion that stock-cat sized bulb might be not exactly right-sized (just empirically comparing to much longer resonators on different catback pipes) to act on wished sound frequencies, so it might aswell be work done for naught, as frequencies affected (widely guessing, but probably very short-length wave, so very high-pitched ones, no?) might not be ones to care for.
But even if making "mini-muffler" in stock cat place .. i probably wouldn't, as imho that relatively-close to engine as stock cats were, might enhance rate of packing material burning out, due exhaust gasses there still being much hotter, no?

[Irace86.2.0]

Originally Posted by weederr33

Sounds kinda pointless unless you live in a place that is strict on mods.

(see location)

The other reason is to create a cheap header that isn’t obnoxiously loud, but still has straight pipe-like performance.

[Irace86.2.0]

Originally Posted by churchx

And pictured seems more of muffler, not resonator.
Resonator acts more by it's size/volume, to cancel out specific frequencies by, well, resonating effect, which is specific to it's size, not by muffling overall noise level by reducing exhaust gases energy, like mufflers do, by different design restrictions to exhaust path (be it walls to redirect several times exhaust path within muffler, or packing material).
And given resonator effects depending on it's size (have no info at hands on accoustic releations) i have suspicion that stock-cat sized bulb might be not exactly right-sized (just empirically comparing to much longer resonators on different catback pipes) to act on wished sound frequencies, so it might aswell be work done for naught, as frequencies affected (widely guessing, but probably very short-length wave, so very high-pitched ones, no?) might not be ones to care for.
But even if making "mini-muffler" in stock cat place .. i probably wouldn't, as imho that relatively-close to engine as stock cats were, might enhance rate of packing material burning out, due exhaust gasses there still being much hotter, no?

I was basing the design off of what I have seen of cut open resonators.



I think you have a good point about mufflers vs resonators, as I am describing more of a muffler in the effect of reducing the volume. Also a good point about the packing getting hot. Even steel wool could melt. I don’t know.

[weederr33]

Originally Posted by Irace86.2.0

(see location)

The other reason is to create a cheap header that isn’t obnoxiously loud, but still has straight pipe-like performance.

lol oh yeah... I'm sorry for you. Well in that case, it could be a viable option. My thinking though, is unless you have a high end packing, wouldn't it all start to vibrate or break apart from the heat?