For the first question i dont have an answer, i know the hmf are loud, so with that said it prob. doesnt have much of a low end gain.
But yes, adding a spark arrestor/quiet core will add some low-end by creating more back pressure.

 

Does anyone know off hand how much a quiet core or w/e its called is on the yoshi pipe?

I'm guessing 20s or so, am I right?

MIke.

 

Im having trouble finding a price for you, i cant even find one. I checked yoshi's site and they dont have one (quiet core).

 

It's called the TEC kit, it consists of 3 different spark arrestors, you pull the endcap off the pipe and just insert one of the three and put the endcap back on. It's probably around $50, but It's worth it, when I go to the sound sensitive dunes I can put the small sparky in and it db's at 93, middle sparky's at 96 and the large opening's at 99.