Soldato
- Joined
- 18 Oct 2012
- Posts
- 8,352
So, finally got around to dropping 20kg's of backbox off the 325.
Gave it a wee spin with nowt on it, just straight pipe and was surprisingly nowhere near as deafening as i thought an unmuffled straight 6 would be, plenty of bark when you floored it but not too much in gentle driving.
Good i thought, wee muffler on there to take the edge off and it wont be booming its way about like your common or garden scooby.
So went ahead, muffler on, sounding nice, bit more tone but not much louder than stock, certainly not raise eyebrows at an mot and wake the neighbors loud.
Problem is, driving home on the motorway and low and behold the hummmmmmm of dreaded drone, slap bang at 2000-2500 rpm cruising.
So, bit of internet digging comes up with helmholtz resonator to fix it, thing is i'm a little unsure of a few things:
1. Where precicely should it be branching off? Some sources say post muffler, but many pics have it just pre muffler.
2. As far as i can guess: 3firings/rev*2250rpm*1/60 gives 112.5hz as my target frequency.
Taking the example speed of sound and calculation gives me a wavelength of 343/112.5 so roughly 30" to the length.
Would that be right? Seems a bit long and might be a tough squeeze to get in. Its fun theory to try and get your head around, very much like the "tuned pipes" i remember you had for wee nitro rc cars and the like.
Gave it a wee spin with nowt on it, just straight pipe and was surprisingly nowhere near as deafening as i thought an unmuffled straight 6 would be, plenty of bark when you floored it but not too much in gentle driving.
Good i thought, wee muffler on there to take the edge off and it wont be booming its way about like your common or garden scooby.
So went ahead, muffler on, sounding nice, bit more tone but not much louder than stock, certainly not raise eyebrows at an mot and wake the neighbors loud.
Problem is, driving home on the motorway and low and behold the hummmmmmm of dreaded drone, slap bang at 2000-2500 rpm cruising.
So, bit of internet digging comes up with helmholtz resonator to fix it, thing is i'm a little unsure of a few things:
1. Where precicely should it be branching off? Some sources say post muffler, but many pics have it just pre muffler.
2. As far as i can guess: 3firings/rev*2250rpm*1/60 gives 112.5hz as my target frequency.
Taking the example speed of sound and calculation gives me a wavelength of 343/112.5 so roughly 30" to the length.
Would that be right? Seems a bit long and might be a tough squeeze to get in. Its fun theory to try and get your head around, very much like the "tuned pipes" i remember you had for wee nitro rc cars and the like.