This is a cut and paste of my exhaust project... it's much nicer over here, so I figured it would fit in...
Since there are lots of great exhaust threads from bolt ons to nice fab work, I thought I would share a simple Borla exhaust project that I'm building for my Tundra and hypothesize/speculate about the stock system a bit. I bought a bunch of Borla exhausts and parts to sell on ebay a few years back, and there are a couple systems still unsold. One looks like it may be a nice fit for the Tundra. Originally a $600+ system for an 01 Dodge V10, it is a single system w/ large 20" muffler and 3" OD tubing.
The stock system is well designed for what it is. Toyota took care to slowly step down the tube size throughout the system to help keep the velocity up and probably reduce noise some. It runs tight off the header, maybe 2.12"? Then jumps to 2.50" to the first converter, then drops to 2.40" out of there, keeps that diameter though the second converter all the way to flanges where the rear exhaust bolts on (just aft the transfer case). The exhaust then drops to 2.12 into the muffler, then 2.75 out to the tailpipe. A better example may be tube ID area in sq in.
3.14" x 2 = 6.28"
4.45" x 2 = 8.9"
4.08" x 2 = 8.16"
3.14" x 2 = 6.28"
muffler ???
tailpipe = 5.43"
That squeeze at the back of the header/top of downpipe is either a big bottle kneck or some type merge collector (can that exist on the tri Y stocker?). The 2.5" downpipe is a nice size, the 2.40" pipe are decent. Then the big drop back to the 2.12" pipes, through the muffler, and out the single 2.75" tail pipe. Since Toyota took the time to produce the system like this, it seems prudent that maybe in order allow nice gains all the way through the power band and not just a big peak number, that running 2.25" duals all the way back might not be the best option...? Instead of dropping to 6.28" pipes, adding 2.25" pipes would give about 7.06", then either a single 3" OD pipe @ 6.42" or dual 2.12" that would give 6.28... Thoughts? other than I am over thinking this...
On to my project, I'm going to try 2.25" back to the muufler, merge collector em', run through the 3" muffler and out the 3" tailpipe.
This system is almost done. The rear section pictured above went in very easily, just had to remove the hangers and relocate. The 2 - 3' of 3" pipe in front of the muffler was cut and removed. This allows dual 2.25" pipes coming from the front to maintain their length and factory tune (speculation) before coming together via a real merge collector and dumping into the 3" muffler. The merge is done, I just need to build the pipes from the front flanges to it. I'll try to get some pics up in the next day or so.
Some pictures working back to front.
Tail pipe
Merge with gusset on the bottom
I need to gusset the hanger, but it will do for now.
As for sound, I like it very much... pleasing to my ears. As for how loud...? I'd call it quiet for aftermarket. Only a hint of sound at lower throttle openings and cruise up to about 2k rpm (but this may change as the muffler breaks in), then one can hear it a little more. Mash the gas and it opens up a bit... still on the quiet - low/moderate side.