What's a Y pipe? What size should I buy? Do I need an exhaust hanger? Can I throw this on myself?

A Y pipe is a connection that merges two tubes into one - and it looks just like the letter Y. On cars that have a single exhaust pipe connecting to the rear muffler, you should option your muffler to include a Y pipe. Some cars have two sets of pipes towards their rear mufflers. These cars wont need a Y pipe. 

You should also try to measure (or find online) the diameter of your exhaust pipe. While most cars use a imperial-sized exhaust (even German ones), there's some considerations you should make. 

A car with a 2.5 inch OD (outer diameter) should order a 2.5in Y pipe. A "butt weld" should be used to connect the two.

A car with a 2.80 inch (example) pipe should order a 2.75 inch Y pipe - the muffler can be partially inserted as a "sleeve" and can be "lap welded". 

An exhaust hanger attaches your exhaust to the body of your car, usually through a metal rod, that attaches to a piece of rubber. This piece of rubber absorbs vibrations. Most exhaust shops will include these for no charge. 

If you are a moderately experienced welder, you can throw these on in an afternoon. MIG or TIG will be fine, although TIG welds will be far prettier. Unshielded MIG welds are generally weak, but can work - we would not recommend flux core MIG. 

The following are some tips for installing hangers, in a DIY setting, with TIG. Most (I hope) muffler shops will know this - but its good to include regardless.

Welding exhaust hangers can be difficult, due to the large differences in metal thickness. Put into layman's terms, the larger the difference in thickness between two joined metals, the easier it is to "cook" the thinner one, and burn a hole through it. U

An .065 wall (standard for mufflers) welding of sheet metal would usually take place at roughly 60 amps. The welder would move the torch (assuming a TIG setting) at roughly 1 inch of weld over 20 seconds. 

A half inch steel plate, in a butt weld, would likely take over 40 seconds to achieve complete penetration at even 110 amps, in a TIG setting. 

The general rule is that 1 amp is used, per thousands of inch of metal.  eg .095 wall stainless, such as something that is used in a roll cage, would be welded at 95 amps. To achieve same speed of welding on a half inch tube, that is otherwise identical, the welder would have to use 500 amps. Of course, this isn't really possible. But, the goal was to explain how welding on hangers can be difficult. If you were to use 65 amps of current on the hanger, it would take literal minutes for the hanger to take filler and achieve penetration.

Hangers can be held onto the muffler with magnets, clamped on, or propped up. 

The welder can point the torch (the heat source) at the hanger, that has more volume. When the hanger begins to melt, the welder can begin to add filler to the hanger. From here, the welder would briefly "flick" the heat source to the muffler - where filler can be added to the muffler side - and then the heat source can resume heating the hanger. A couple times of this will allow for proper attachment between the hanger and the muffler.

Note that you absolutely cannot expect even penetration between a muffler and its hanger - and that this is normal. When one side of a joint is substantially thicker the other, the strongest a weld will be is the thickness of its thinnest part - meaning that penetration (liquification and solidification) of the hanger at a depth of .065 will be completely adequate. It will take more time to achieve penetration at a depth of .065 on a large piece of metal, compared to a small one. The rest of the piece of metal will wick away the heat from the source. 

The thickest and strongest parts of the mufflers will be the edges of each "baffle".

 

It certainly isn't right, but there's many ways to hang a muffler. I have personally helped my friend put the exhaust up on his '95 BMW 525i Touring with a steel gardening wire. It cant be that wrong if it works. We wont judge.