How much do cat, converters muffle?

[Petrus]

In our car the OEM midpipe with the cat is quite restrictive. Changing to a sportscat or decat thus makes sense to improve flow.

When I fitted my no-muffler on a decat pipe I was a bit taken aback by the noise level. It was really too much. Not that it bothered any neighbours but it made revving the thing a stressfull experience. So refitted the cat and it reduced the noise to half, which should be some 3 dB(A).


Digging through noise stuff found the specs. for checks at the road side (about 70 cm from exhaust at 45 degrees):




For as far as I can find, the legal max. level measured this way is the db(A) as per technical details + 4 dB(A).
I have not found this homologated figure (yet) so no base line 

Two MR2s measured with the same meter:
- All OEM with TTE/Remus muffler: 87 dB(A) at 5300 rpm.
- PPE cai, PPE 4-1 header, 200 cell sport cat, TTE/Remus: 100 dB(A).

I am a bit surprised about the above as it is the same muffler with stock vs sports cat   but then it is not known how much sound deadening is still in them.

I refit the OEM cat and muffler before technical inspection so it shoúld be ok but as per next year the inspection will feature a measurement. I díd fit a decat header and a TRD like inlet however and that being at the same side as the exhaust tip the mod will be picked up by the meter.

My question is what your experiences with the sports cat and other mods are.

[Dev]

There are a few things that is responsible for noise and performance. The cat material can be one of them but the main one is the pipe diameter and pipe length. Increasing the pipe diameter and decreasing its length can increase power at the expense of more noise but up to a certain point.   
 In our cars the downpipe has chokes built into the flex section that reduce the pipe diameter greatly. If you change the flex sections you will increase the noise as well as the power. Also it was found out the area where the pipes join before it goes into the cat is smaller in diameter compared to a sports cat.
 
 You can get a genuine 8hp to the wheels with a sports cat which is a lot more than any other bolt on engine mod that claims power but is immeasurable because it's within the error of the dyno. 

 To counter act the effects of the sport cat you need a good muffler. Generally the TTE does well as it's quiet to begin with so the increase in sound is tolerable. 

[Petrus]

Thanks Dev and it doés interest me to know what a header, cat/sportscat/decat, muffler does for the ponies in respect to the weakest link chain.
On my car I tried various combinations:
The OEM cat is indeed thé bottle neck. With it fitted precat or decat header makes véry little difference and the muffler nó difference. In power that is.
With a decat pipe the straight through no-muffler did result in a much livelier engine but the OEM one must be quite good in flow and the small difference in ponies was belied by the massive difference in noise.

In thís thread though I would like to dig up info on what the decibel meter has to say about it.

[Dev]

It depends. Some header designs are phony as they have not been tested and the only gains are being less restrictive. Some like the PPE that are equal length have been proven to correctly time its pulses so that there is a scavenging effect that yields the most amount of power however its all a trade as you might be trading low rpm torque for high rpm horsepower. To get the most out of it requires a tune for some extra which is not worth the cost or the hassles.

 There is nothing free here but just putting on a less restrictive exhaust may yield power just for being less restrictive but it might not be optimized by design. On the whole however anything after the cat is not going to make a tremendous difference anyway so in my opinion sound quality in terms of tonality of the exhaust is far more important to those that value complements. Nobody likes to hear an annoying sounding exhaust with bad tone.

[Petrus]

The 1ZZ-FE is not a top end engine anyway. The head and timing are designed for ease of use; low and mid range. Fitting a 4-1 is probably less useful than an unequal length manifold that will spread/soften the interference of the pressure pulses. It will also by the way mellow the note.

Thát the sound and more specifically what the meter reads is what I want to know a bit more about.
For one becasue the plan is to fit the decat midpipe again in combo with a way better muffler than my no-muffler but mpre importantly to find out what the dB(A) level is with precat and decat header.

The intake I will measure myself as that is easily swapped out. Even the temporary refitting of the mud guard duct.

The thing is that per coming year the periodic inspection will always include a dB(A) measurement and better be well prepaired than an automatic rejection.

[Dev]

 I am glad I do not have any of those sound ordnance problems. Some other states like California have them where the police will pull you over if they think your car or motorcycle is too loud. People in my area are much more accepting because it's not all the time and they like car and bike culture. If the sound is measured at idle my car would easily pass but if its revved it would fail spectacularly according to our laws.

[shnazzle]

The loudest car I've heard to date was owned by our faithful @Wabbitkilla (as if he's going to respond to that tag...).
I believe he had a Zero manifold, 100 cell? And the Che lotus style exhaust. It was insane. What also doesn't help is the intake. I eventually ended up with his intake actually, maxbore throttle body (which I left on the car @MrChris has) and a hurricane cone intake behind battery fed directly from side vent. 
@ChrisGB is that what it had when you got it?

You could hear Nic coming a mile off.

I had the same setup but with the TTE and a 200 cell. It was loud. Quite loud indeed.

I put stuff on in order so I kind of know what makes it loudest.

1) installed TTE exhaust. Got louder, but it was quite subdued actually.
2) added intake. Entering obnoxious level. Definitely didn't go anywhere near as hard as it sounded. Bit embarrassing. 
3) added manifold. Quite a bit louder with the wider equal length runners. Now fully in "I can hear you coming all the way down the road" 
4) added sports cat. With that final addition even idle was a lot. You could hear me coming from a distance and christ it didn't half scream at full chat. Lovely. But... Loud. 

Power wise... Cat. Definitely 

[shnazzle]

Here's my full series of mr2 noise clips at various stages of """"tune"""

Loudest - all mods
https://youtube.com/shorts/eodJA8giZc0?feature=share

zero mani, 200 cell, tte exhaust. Don't think I had the hurricane in at this point. Took it out
https://youtu.be/yK94lbCHQrg
https://youtu.be/6M9QxvrNfiA
https://youtu.be/t48UV45OfJE

TTE + hurricane, all else stock
https://youtube.com/shorts/cGnfwVR4Qcc?feature=share
https://youtu.be/--1hrQn7CTU

TTE and cone filter (not the hurricane. Chopped stock MAF and cheap cone) 
https://youtu.be/LMNelq33uXk

Just TTE all else stock. Stock manifold but gutted pre-cats
https://youtu.be/WY6PFPXGvng
https://youtu.be/nCfwLxYSjc8

[Petrus]

Thanks Patrick.
Double thanks for the sound clips. Studying them.

Makes sense.

The as new TTE should be near OEM with a different note.

Sorts cat is practically decat as far (de)restriction thus (de)muffling goes. The OEM cat (edited: - pipe) is quite restrictive. The noise level difference is about double.

The observation about the larger diameter manifold tubes is spót on! Noise level is related to diameter so the bigger pipes of the Zero should be audible. The equal length has more effect on the note than the level.

The last observation confuses me. Should that not be powerwise sport/décat?!

[Dev]

If you remove the cat contents from the OEM it's not going to be extremely loud just like if you remove the precats from the header. We know this because some have done it already. The chokes in the flex section is where most of the noise suppression is, next is where the two tubes connect is narrow. The diameter is so small and that is why it is the bottle neck.
 Essentially the OEM downpipe is where a lot of sound suppression takes place by the entire design not just the cat material. I also believe it acts like a tuned resonator to eliminate harsh sounds. Once that is eliminated it can get loud but if you have the right exhaust it is a good loud.

[Petrus]

Quite a lot of clear comparative info,

Also one clear lesson learned from the @Shazzle files is that I will stick the oem intake horn back on too before periodic inspection. Maybe sticky tape the duct back in.

[ChrisGB]

@ChrisGB is that what it had when you got it?

Not a car or setup I was ever involved with.

In terms of power / noise trade-off, I saw about 6bhp replacing the stock exhaust with the Che single exit. Noise was slightly louder but not offensive. PPE manifold and cat onto Blue flame exhaust was definitely a lot louder with an annoying drone. PPE into a diameter matched single carbon resonator was insanely loud and sounded rubbish, so that needed a second resonator to soak up noise. All of these low back pressure exhausts made the same power on the PPE manifold and cat (156/8 from memory) with no loss of mid-range torque.

The best way to silence a 1zz is to put a turbo on it. This allowed me to run one small resonator and still have a decently quiet system. I think this was my favorite exhaust build, it was a carbon resonator with all pipe work joined with springs on slip joints (Pete Ellis work is stunningly good). The biggest advantage of this system was it's 3.2Kg cat back weight, which helped with handling.

[shnazzle]

Not a car or setup I was ever involved with.

In terms of power / noise trade-off, I saw about 6bhp replacing the stock exhaust with the Che single exit. Noise was slightly louder but not offensive. PPE manifold and cat onto Blue flame exhaust was definitely a lot louder with an annoying drone. PPE into a diameter matched single carbon resonator was insanely loud and sounded rubbish, so that needed a second resonator to soak up noise. All of these low back pressure exhausts made the same power on the PPE manifold and cat (156/8 from memory) with no loss of mid-range torque.

The best way to silence a 1zz is to put a turbo on it. This allowed me to run one small resonator and still have a decently quiet system. I think this was my favorite exhaust build, it was a carbon resonator with all pipe work joined with springs on slip joints (Pete Ellis work is stunningly good). The biggest advantage of this system was it's 3.2Kg cat back weight, which helped with handling.

Ah I think it was Nigel actually that bought his car. Apologies.

Helen's turbo was NOT quiet haha. That SP240 backbox was "boomy" to say the least.

Pete Ellis' work is a bit high spec for my wallet. But money no object and I wanted to give the Airtrek a nice new full exhaust, that's where I'd love to take it. Downside of bigger cars.. Much more metal needed. 

[Petrus]

Thanks Chris.

In terms of power / noise trade-off, I saw about 6bhp replacing the stock exhaust with the Che single exit.

Is this behind the OEM cat?

The best way to silence a 1zz is to put a turbo on it.

No doubt about it for basically any n.a. : The turbo is driven by energy from the exhaust gasses. That part of the energy (pulse, speed, heat) does not need to be muffled. In the wolrd of noise regulatiosn it is a briljant aspect of the turbo; really the equivalent of something for nothing. It even compensates some of the weight by needing less muffler.

Alas, again not a path I can walk. I am stuck with reducing the pumping losses.
That is, also again, not the thing for me with thñis thread: I am trying to identify the potential noise issues for the mandatory noise check of the periodic inspection.

The secondary agenda which has developed is learning from the shared experience for the illegal daily setup; the ´best´ compromise between noise, weight and ponies.

The biggest advantage of this system was it's 3.2Kg cat back weight, which helped with handling.

Which is why I refitted the OEM cat to tame the noise in favour of the lightweight no-muffler. The muffler sits high above and behind the rear axle.

[ChrisGB]

Yes, behind the stock cat / precast.

[Petrus]

Yes, behind the stock cat / precast.

Thanks for the info.
6 hp is quite a gain    with the/another main botteneck (the OEM cat mid pipe) still in.
I most definitely not expected that.

I read somewhere else that a swap from precat header to an ubiguitous after market one netted 3,5 hp.

Dev wrote that the down/mid pipe can unleash 8 ponies.

A pity that it is not cumulative   
Applies to noise more ´effectively´     Noise gets more reduced by restrictions than flow. Hence the multiplying of noise for small numbers of ponies.
Hence the after market header on mine worries me a bit.  Fingers crossed the OEM cat pipe and OEM muffler negate the derestriction a bit. Hence my lesson learned about the inltake. No leeway left there.

On the powah side though,,,, good hopes then for my next plan.

[Ardent]

The best way to silence a 1zz is to put a turbo on it.

@shnazzle Just like you have been telling me over the years.
The turbo is smoothing out the the other bits to end up with a civil sounding zorst.

[Dev]

Genuine 8 wheel horsepower is not small. The reason why it seems small is primarily because a lot of mods are all hype with inflated hp numbers and dyno operators that scale to please the customer and then its posted on a forum. This is not brake hp this is to the wheels and it's not all up top. You will be lucky if you get that from a tune but there are those that estimate hp based on cumulative bolt ons but once on a real dyno the reality is disappointing.

 The OEM cat is so restrictive that it causes a 20hp drop for those that perform cheap 2ZZ swaps. This is where the myth that the 2zz is just like the 1ZZ before lift. 
 It's worth doing if you want value but it should be pared with a quiet exhaust. Quiet exhausts weight more.

[Petrus]

Genuine 8 wheel horsepower is not small.

Nor does it seem so to me.
On a aub 140 hp n.a. it is a world.
I don´t even have to ´believe´ it: For one I felt the difference when I had the decat pipe under and secondly the various dyno results bear witness even though invariable mixed in with other mods.

Anway.
Will try do a comparative measurement of the intake first.
Hopefuly before x-mas a comparative sound check of a set up with decat pipe and one with the OEM cat pipe.
The decat set up will hopefully return the sense of the intake mod. There is not much sense in allowing the engine to breath in more when it cannot breath more out.