Anyone know?

 

Are you talking about the sound chamber or the whole thing including the inlet pipe?

I would guess the sound chamber is at least around 18 inches in length.
Most aftermarket mufflers have sound chambers around 12 inches in length but wider than stock.

 

the case length of the muffler is 20 inches.

 

Do you guys think a 22 inch muffler will fit as well? Let me know. Thanks.

 

22 inch will fit fine I had 24" muffler on my 96 I30 with plenty of room. It just depends where you want to cut the oem pipe to fit your muffler with the way you want the tip to sit. You can go either way going smaller by adding pipe to fit or cutting away some to fit a larger one.

 

Thanks Tim96. Now I just need a place to buy one.