Question for anybody who can measure EGT please?

[s2_wot]

Hello, looking for a bit of assistance on EGT's at cruise speeds on road cars with ABY / ADU engines. I'm not recording EGT yet but I think quite a few forum users have the facility.

Background to this is to calculate the speed of sound in the exhaust. It varies with temperature. I want to calculate the 1/4 wavelength to accurately determine the length of the side branch resonator needed to reduce drone at cruise speeds.

50 / 60 / 70mph (80 / 100 / 120km/h) 6th gear


30mph (50km/h) 3rd gear
40mph (60km/h) 4th gear
50mph (80km/h) 5th gear
50mph (80km/h) 6th gear
60mph (100km/h) 6th gear
70mph (120km/h) 6th gear
80mph (140km/h) 6th gear

mph / km's are approximate & maybe someone who's monitoring these things all the time would know from experience the approximate EGT's.

Brief description of the engine / exhaust setup would be very useful too.

Thanks in advance

[A80Avant]

i can tell you a few EGTs but at the moment they may be an approximation. It is difficult to test with this weather but:

30mph (50km/h) 3rd gear= around 600C
40mph (60km/h) 4th gear= around 580-600C
50mph (80km/h) 5th gear= around 630C
50mph (80km/h) 6th gear= around 620-650C
60mph (100km/h) 6th gear=around 700C
70mph (120km/h) 6th gear= around 720C-750C
80mph (140km/h) 6th gear= around 760-790C

these tend to depend on load though.

once the weather clears i can try and test for you.
the setup is ADU engine with 3076R turbo, SQ EM and EGT sensor on the EM collector, 3inch downpipe, dual cats 200cci, 2.75inch cat back with 2 boxes.

[driftin jo]

As said above this is going to depend on load , as you are most bothered about cruising speed
I would just say 650 deg thus giving you a sound speed of 609 m/s ~ 2000 feet per second , 1360 mph . A mate of mine made a resonator a wile ago and he used 2000 feet fer second for the speed of sound and as this works back to 650 deg this seems a good starting point.
The other thing he did was to make the box in two halves so that the one was sliding over the other so that he could tune the box on the car for best result before welding it up .

See diagram .

[JP]

I can't see how the temp can have that great an effect as I get motorway drone at 3000rpm irrespective as to whether I'm in 3rd, 4th, 5th, 6th goes away over 3500rpm and below 2800rpm. If temp made such an issue I'd expect it to behave differently in different gears as there is a different loading. Personally I think it comes down more to the shape of the system and the length of the straights relative to the diameter of the pipe. By lenghtening and shortening the resonator/muffler all you would be doing is changing the length of the straights which would change the point of resonance in the rpm band. Just an opinion based on my own personal experience, of course I could be totaly wrong on it all, as I'd love a solution to the problem as I do a lot of motorway miles and am contemplating going back to sock rear muffler with a bypass system actuator activated for WOT.

[driftin jo]

Temp won't have a massive affect as it is not varying that much at cruising speed ,
that's why I said just call it 650 deg for calculation purposes . You need to know the temp as
at 650 deg sound travels almost twice as fast as it does at 20 deg (340 m/s ) .
the point of making the box tunable is so you can get the best all round result as far too many factors come in to it to just calculate the perfect resonator box to stop drone at 3000 rpm. The temp is reducing the further it gets from the down pipe for example thus the sound wave is slowing down as well. My friend who made his resonator was able to almost totally remove the drone from his exhaust.

[s2_wot]

Thanks folks (especially A80Avant for recording them for me), I was thinking it'd be about 500 to 700. For my own benefit I'll do a calculation based on ambient temperature, the relevant speed, the surface area of the pipe and the temperature differentials to see what the temperature drop from the top of the down pipe to the location of the resonator..

Getting rid of the lower frequency noise is something that a normal straight through silencer can't do very well without being extra long and the OD of the silencer being say 3 times the OD of the pipe. Even at that they are designed for high frequency noise.

@ Driftin jo the slip joints are the only way to tune it for the car I completely agree.
It's always nice to be in the ballpark tho'

It is also possible to get a sizeable noise reduction in the lower frequencies by putting in a dead end tube somewhere in the system that's tuned to exactly wavelength/4. The pipe doesn't need to be perpendicular to the exhaust pipe as shown. The limitation on the design is that it's only really able to work on a specific frequency. Identifying the particular frequency to target is beyond most diyers including myself as I don't have all the equipment.

With this type of tube the EGT isn't important because there's no exhaust gasss flowing in this section of tube. Just sound waves. This is a big help in shortening the length of the tube because I think you could assume ambient temps (and therefore shorter wavelength)

Here are the engine frequencies that need to be targeted and the speed of sound at differing temperatures.

RPM Frequency (EFR) for 5 cyl 4 stroke
2700 112.50 Hz
2800 116.67
2900 120.83
3000 125.00
3100 129.17
3200 133.33
3300 137.50
3400 141.67

Temp°C Speed of Sound(m/s)
100 387
200 436
300 479
400 520
500 557
600 592
700 625
800 656
900 686
1000 715



Article attached shows some typical resonator designs albeit for static engines with static load. Hence the point of having to make these things tunable rather than trying to calculate every detail.

More food for thought in relation to the speed of sound within the exhaust. Stainless steel has a much lower ability to dissipate heat than conventional exhaust materials so all things being equal the wavelengths will be longer and harder to manage in a stainless system.


EDIT: Those figures didn't display as intended, I'll post an excel chart later.

[A80Avant]

the figures depend on where the sensor is. if you place it on the downpipe, you will have the 500-700ish values that you were expecting

[s2_wot]

the figures depend on where the sensor is. if you place it on the downpipe, you will have the 500-700ish values that you were expecting

That's ok, they're exactly what I was after just to make sure I wasn't barking up the wrong tree.

[Error404]

are you sure the speed of sound isn't slower at higher temperatures?
Since the gas density is lower the sound waves travel slower just as at higher alititude?

[s2_wot]

are you sure the speed of sound isn't slower at higher temperatures?
Since the gas density is lower the sound waves travel slower just as at higher alititude?

Well I'm using the speed of sound in air rather than the speed of sound in exhaust gasses so there's possibly a correction factor of something small needed.

However the speed of sound does increase as temperature increases.
here's a link: http://www.sengpielaudio.com/calculator-speedsound.htm

EDIT: In an ideal world it'd be great to break the noise and the gasses into those seperate components. Design a pipe to take the exhaust gasses out the most efficient route and bring the noises off to another corner and sort them out.

[Error404]

I don't understand what these people are saying:

"For an ideal gas the speed of sound depends only on the temperature and
is independent of gas pressure"

This cannot be accurate since no sound is transmitted in a vaccum.

[s2_wot]

at this "This is a site for sound engineers. We are interested in the speed of sound on Earth at places where acoustic instruments or voices are used. The speed of sound of
atmospheric layers, as in 100 km altitude, or close to the vacuum is not of interest."

This is their logic regarding pressure & density.

"Statement: The static air pressure p_ and the density ρ of air are proportional at the same temperature.
The ratio p_ / ρ is always constant, on a high mountain or even on sea level altitude.
Forget the air pressure, but remember how absolutely importantthe temperature is."

However now I have to think about pressure & density within the exhaust, they both obviously vary; but do they vary proportionally?

@Error404 do you think the speed of sound would be signifigantly different from those shown further back in the thread? I didn't think so but now..

[Error404]

in all honesty I don't know enough about it to comment anything further than that I don't think what these guys are stating is painting the complete picture, since air density also plays a role, which in turn is a function of air temperature. Its all about the viscosity of the gas (air) as far as i understand it.

[s2_wot]

Internals of Resonator / Reactive Silencer. Tuning the length of the different chambers to the wavelength is the key to the sound of silence. Not my photo BTW.

[s2_wot]

Magnaflow's XL Silencer

http://www.magnaflowstainlesssteelexhausts.com/mufflers/xl-turbo-chamberd-mufflers.html

Anybody know of a forum user that has one of these specific silencers fitted?