Harry,enigma57 wrote: ↑Wed Apr 10, 2019 4:37 amThanks, Paul. That's a very informative chart you posted. Just trying to figure this all out as to practical application with respect to my present (and last) build.
With a four stroke engine, the crankshaft rotates twice for every power stroke, or one power stoke for every two revolutions of the crank. So, if the crankshaft is turning 2,000 RPMs, that would be 1,000 power strokes (firing of spark plugs) for each cylinder per minute.
So for an 8-cyl. engine running at 2,000 RPMs, the plugs would fire 8,000 times per minute (1,000 times per plug). For a 6-cyl. engine running at 2,000 RPMs, the plugs would fire 6,000 times per minute (1,000 times per plug). And for a 4-cylinder engine running at 2,000 RPMs, the plugs would fire 4,000 times per minute (1,000 times per plug).
In my case, I have a 292 inline 6-cylinder engine bored 0.040" over. 3.915" bore X 4.120" stroke = 296.13 cu. in. displacement exhausting through split HP exhaust manifolds into a 2-1/2" dual exhaust system having an H-type crossover (balance) pipe. By necessity (due to layout of piping beneath car)...... Mufflers (in this case, chambered exhaust sections) are staggered as mentioned by Craig, so that should help cancel drone a bit.
And yes, I plan on including one (or more) pair of side branch/helmholtz resonators......
I worked heavy construction for many years as a pipefitter and plumber installing piping in high rise buildings and large industrial projects, so I see these acting more or less along the same lines as air chambers fitted at the end of water supply lines to multiple fixtures (to prevent water hammer). The critical thing being placement and volume. As long as placement was correct and diameter was equal to (or greater than) piping in supply line and met (or exceeded) min. volume required to prevent water hammer...... You were good to go.
For my car...... Cruise RPMs at 70 MPH with overdrive engaged will fall in the 2,000 to 2,100 RPM range depending upon final choice of tires.
So bottom line...... How do I determine drone RPM range for 6-cylinder engine and best address that? Does cylinder displacement and/or exhaust system diameter enter into it, or are we looking entirely at frequency of impluses and method(s) of cancelling sound waves?
I think it important to state again that I am a spreadsheet hobbyist and no expert in the realm of drone suppression systems. I just like to play with numbers. Having said that, I do attempt to understand a subject.
To the best of my knowledge and available public data, drone frequencies occurred between 100 and 150 hz regardless of cylinder count. Drone in a 6 cylinder motor should occur somewhere between 2000 and 3000 rpm. Exactly where in that rpm range on a given vehicle can only be known by testing. It is important that the suppression system be designed to match the drone frequency. The system will have limited range of frequency suppression. You can not guess and still obtain maximum suppression for a individual vehicle other than by chance.
The tube diameter only matters on the suppressor. It changes the tube end effect distance which is subtracted from the drone wave length calculated on the spreadsheet. Quarter wave tube length=Drone wave length/4-(1/4 wave tube dia*.4)