Chanito's stock muffler modification

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OK this is the Chanito stock muffler mod, but you are doing it under your own, so do not come to me saying it does not increase power or does not sound like you want it to.
This is how a stock muffler looks if you have X-ray vision


As you can see the exhaust has to turn at the end chamber and goes into the middle chamber, the walls of this chamber have some fiberglass and an extra perforated wall around it to quiet the exhaust down, it also allows the gas to expand preventing it from going back to the exhaust valve (this lenght of tubing is tuned to the engine) once the gas have expanded it goes to the front chamber where it cools off slightly, turns around and goes into a pipe connecting the end chamber and front chamber, this pipe will take the gas into the rear chamber where it will cool even more and exit the muffle via the tip.
The idea is to provide some extra passage for the gas in the middle chamber to exit into the rear chamber, therefore reducing back pressure without messing with the primary lenght of the exhaust (the pipe from the engine to the middle chamber)
First you need to remove the stock tip by using a 1 inch holesaw and drill it out, this will allow later to fit a bigger tip and gain acces to the wall separating the middle chamber and the back chamber, then use a 1/8 drill bit and drill 4 holes in that wall, you want this holes low as it will be cooler gases there than on the top, so if you can dril them at the same height of the tip hole great, this wall is heavy gauge steel so be patient, once the four holes are drilled just weld a 2 inch piece of 1 inch pipe (the one they use for electric wiring is great and cheap). make sure half of it is inside the rear chamber and presto a higher flowing stock muffler