Problem exhaust drone: Solution 1/4 wave, or Helmholtz resonator?

[oldeskewltoy]

Problem: engine drone 3500-4000, it is quite bad through that zone, so lets say 3750 rpm + or - 250 rpm.


I've been doing some research into side branch or 1/4 wave resonators - closed "J" shaped pipe of SPECIFIC length added to the system.





Some people also use Helmholtz resonators (pipe leading into closed muffler)




Each of these has their own formula (no, I have not researched each's formula yet) The reason I have not checked into both thoroughly yet is packaging of a Helmholtz resonator, and placing which ever device in as optimal a location** as possible - close to the source/engine.




So based on optimal placement, I was thinking of tapping into the very beginning of my Brave exhaust with a 1.50-1.75" diameter pipe, and running it the prescribed/calculated length back....




Initial distance is around 30"... or so I was told. I don't trust this - I'd prefer YOUR help with calculations...

So what length pipe do I need to target 3750 rpm??

[Ivan141]

Just make sure it's not the exhaust vibrating against something that's causing the drone.
Read a whole topic on these resonators on some porsche forum out of interest, and in the end
after much faffing about with resonators the problem turned out to be the exhaust mounting.

[Dave W]

Dan
See if you can get a copy of "Scientific Design of Exhaust and Intake Systems by Philip Smith & John Morrison" from your local library.
The location of the "J" pipe in the system and distance from the muffler will effect the resonance frequency as much as the length, i.e. volume, of the "J" pipe. They appear to be most effective when install right after the exhaust manifold. Dave W

[oldeskewltoy]

(05-17-2017 01:47 PM)Dave W Wrote:  Dan
See if you can get a copy of "Scientific Design of Exhaust and Intake Systems by Philip Smith & John Morrison" from your local library.
The location of the "J" pipe in the system and distance from the muffler will effect the resonance frequency as much as the length, i.e. volume, of the "J" pipe. They appear to be most effective when install right after the exhaust manifold. Dave W

still doing research.......

http://www.f1technical.net/forum/viewtopic.php?t=12772

[jondee86]

I have wondered if something like this could be implemented on a 4AGE ?

Quote:A four-stroke power valve is a device fitted to four-stroke engines that
constantly adjusts the internal diameter of the exhaust system to better
suit engine speed. At low engine speeds the wave pressure within the pipe
network is low. A full oscillation of the Helmholtz resonance occurs before
the exhaust valve is closed, and to increase low-speed torque, large-
amplitude exhaust pressure waves are artificially induced.

This is achieved by partial closing of an internal butterfly valve within the
exhaust at the point where the primary pipes from the cylinders join. This
junction point essentially behaves as an artificial atmosphere. The alteration
of the pressure at this point controls the behavior of reflected waves at this
sudden increase in area discontinuity. Closing the valve increases the local
pressure, inducing the formation of larger-amplitude negative reflected
expansion waves.

A servo motor controlled by the ECU opens and shuts the valve.[1] The
valve goes from being almost fully closed at idle speed, through to fully
open at higher engine speeds. This ensures superior low to mid-range
performance, more linear power output and reduced exhaust noise levels
while the valve is in its reduced opening position.

It might even be a solution for the mid-range drone

Cheers... jondee86

[Bean]

Have the closed of part of the pipe as a sleeve going over the rest of the construction. That way you'll be able to adjust the length until you get it right.
It will take quite some time testing but honestly no amount of calculations will get it right. The calculations will only give you a starting point, as there are way to many factors involved which you can only approximate for.