Its cheap to buy a jett muffler and save time or spend more more money this way. get a long header from MACS then make a cone that fits over the header then machine a step in that cone and weld on a aluminium tube and then an end cap with a small stinger. hard part is finding the length of header you need for the 1/4 wave pipe you just made. easiest is to just order the jett muffler. you can get the red ones, gold ones or the black quickie ones. red is 15,500 to 17,000 on ground. gold is around 17,000 to 19000 and the black is 18500 to 21000. all these are average numbers as I have seen some red one go as low as 14000. oh these are for the 25 size and 45 size cased engines. The red one for the 90 to 120s work well in the 9000 to 11000 range