Re: Making a muffler
Posted: Tue Apr 10, 2018 9:52 pm
That sounds really good. Nicely done.
Home of Racing's Best and Brightest
https://www.speed-talk.com/forum/
I saw that on google news a few days ago. Good stuff.ptuomov wrote: ↑Wed Mar 13, 2019 9:32 am This looks extremely interesting, if you're thinking about making racing mufflers:
https://www.eurekalert.org/pub_releases ... 030619.php
Bingo!
its hard to make anything else sound like a v twin with a miss. LOLDavid Redszus wrote: ↑Tue May 21, 2019 8:04 pmBingo!
The exhaust pipes should end at a certain tuned length from the head. This tuned length is far too short for most vehicles.
The trick is to insert a large diameter resonator at the proper distance, and then run free flowing pipes to the rear of the car.
I built such a system for a road racing BMW for a race at Road Atlanta. It easily passed the track noise limit but was very noisy inside the car. Sheet metal floors resonant quite a bit. Fastest car in class. But then it rained and the driver crapped his pants.
Prof Gordon Blais devotes an entire chapter to the design of noise cancellation exhaust plumbing in his Four Stroke book.
The required measurement inputs are:
Inlet insert diameter
Inlet insert length
Exit insert diameter
Exit insert length
Tailpipe length
Resonator diameter
Resonator length
Exhaust gas temperature
The program will predict the dB noise attenuation and frequency range output.
With any kind of luck (and patience) you could make almost anything sound like a Harley.
I think you mean mass flow. Sound attenuation does not require a reduction in mass flow properties, although some designs (i.e. SuperTrap) certainly do.ptuomov wrote: ↑Wed May 22, 2019 7:47 am A cross plane V8 without any crossover between banks isn’t too far from a pack of Harley’s, no?
During this project, I think I figured out that any methods for muffler design that don’t take into account the mean gas flow velocity aren’t in practice very predictive.
I meant that if there's no gas flowing thru the muffler, the insertion loss is very different compared to the case in which gas is flowing fast thru the muffler.David Redszus wrote: ↑Wed May 22, 2019 10:51 amI think you mean mass flow. Sound attenuation does not require a reduction in mass flow properties, although some designs (i.e. SuperTrap) certainly do.ptuomov wrote: ↑Wed May 22, 2019 7:47 am A cross plane V8 without any crossover between banks isn’t too far from a pack of Harley’s, no?
During this project, I think I figured out that any methods for muffler design that don’t take into account the mean gas flow velocity aren’t in practice very predictive.
Flow reduction is normally encountered when pipe diameters, pipe bends and pipe lengths are not considered. What is the total flow reduction (head loss) from the head to the back end of the vehicle?
What is the diameter of your exhaust pipe(s)?
What diameter exhaust pipes are you running into the resonators?ptuomov wrote: ↑Wed May 22, 2019 11:04 amI meant that if there's no gas flowing thru the muffler, the insertion loss is very different compared to the case in which gas is flowing fast thru the muffler.David Redszus wrote: ↑Wed May 22, 2019 10:51 amI think you mean mass flow. Sound attenuation does not require a reduction in mass flow properties, although some designs (i.e. SuperTrap) certainly do.ptuomov wrote: ↑Wed May 22, 2019 7:47 am A cross plane V8 without any crossover between banks isn’t too far from a pack of Harley’s, no?
During this project, I think I figured out that any methods for muffler design that don’t take into account the mean gas flow velocity aren’t in practice very predictive.
Flow reduction is normally encountered when pipe diameters, pipe bends and pipe lengths are not considered. What is the total flow reduction (head loss) from the head to the back end of the vehicle?
What is the diameter of your exhaust pipe(s)?
From some old mesurements:
Static pressures measured normal to flow, in psi:
Barometer 14.80
Turbocharger Suction Pressure (ABS) 13.85
Intercooler Pressure Delta (DIFF)1.30
Intake Manifold Pressure (ABS) 30.69
Downpipe Pressure (ABS) 15.97
So say 1.2 psi back pressure.
It's dual 3.5" system with that merges the flow twice for sound suppression. Two 3.5" resonators, merged cross-over, two 3.5" mufflers, and a big muffler at the merged tail pipe.
Reviewing a silencer design program, I find that a straight thru, perforated tube, design will attenuate noise at specific frequencies, without flow loss. The issues to address are: packaging, attenuation targets by dB and frequency. Other design factors are gas temperature and wall thickness.