Poor Stock Exhaust Design
 

The Mazda Engineers really screwed up this exhaust on a 2006 Mazda 6 V6 3.0 litre (I hope that person got fired). The top 2 pictures show this terrible stock exhaust design. The rest of pics are the updated customized exhaust. The pic that says "Rear Cat" is actually the Rear Pre-cat.
On the Stock Exhaust, the Rear Pre-cat actually flows toward the front, then at the last point it actually comes 90 degrees to the front pipe at some point after the Front Pre-cat: This causes interference in flow between front & rear pre-cat. Exhaust is supposed to flow to the rear in a "Y" formation not a "T".
After this it then flattened and came to 2 sharp close bends just before the Rear main cat causing more flow problems (pic 2).
What problems does this cause?: Engine misfires, no exhaust scavenging (when driven hard). I actually got a CEL for a Misfire @ around 5,000 rpm in 3rd gear entering the highway with very poor acceleration around this point (just over 20,000 miles on car). After changing plugs, ign coil, injector it still misfired. They then changed the fuel tank (warped). Still misfire. They finally changed the Pre-cat/exhaust manifold and misfire was gone. However, I did not trust it, so I changed that piss poor design and changed it to a "Y" and still have both pre-cats (I have to pass emissions). I took it 1 step further and increased the diameter of the exhaust from 2.25" to 2.5" after the "Y", including the Rear Main Cat (Magnaflow). Now it flows and sounds great. No more misfires. Definitely gained HP and some Zoom Zoom. It's been a few years since doing this and I am glad I did. If yours is like this do yourself a favor and change it.

Video:
More Exhaust pics:
Mazda Forum - Mazda Enthusiast Forums - UseYourNoggin's Album: 2006 Mazda 6 V6 3.0 Exhaust, Stock & Modified

https://www.mazdaforum.com/forum/mem...-flow-2219.jpg

https://www.mazdaforum.com/forum/mem...bends-2218.jpg

https://www.mazdaforum.com/forum/mem...sover-3107.jpg

https://www.mazdaforum.com/forum/mem...e-cat-2216.jpg

https://www.mazdaforum.com/forum/mem...-cats-2213.jpg

https://www.mazdaforum.com/forum/mem...-cat2-2214.jpg

https://www.mazdaforum.com/forum/mem...-2-25-2212.jpg

WOW, they must have hired the old Ford guys who designed the stock exhaust for the '92-'94 IDI Turbo, that was a very flat exhaust pipe also.

Update: 2007 as well
 

UPDATE: I was at a friend's place on the weekend. He has a 2007 Mazda 6 HatchBack GT. His exhaust is the exact same. :mad: The pipe from Rear Pre-Cat goes toward front and joins the pipe at a 90 degree angle.
The piss poor stock design was not changed in 2007. :eek: He has not had the misfire issues as I have. :cool: He does have the Magnaflow Cat Back Exhaust but it does not sound as good as mine do to my exhaust changes after the pre-cats. :D

Noggin you did some great sleuthing there and your muffler shop did a fantastic job.

When a manufacturer comes up with a screwy design like that it's probably to save about $1 per car. If one million cars are sold... you do the math. But in this case I can imagine that doing it right like noggin did would have been the less expensive way: fewer parts and easier to assemble!

Cheers! (I had a few on you)

THANX! :) It was my idea. ;) I saw the short Y-Pipe in a catalogue (dual 2 inch to single 2.5 inch) and it was great. I had it done at an Aftermarket Performance shop where they change/upgrade exhausts all the time. They suggested to buy a 2" Exhaust Donut which a piece of exhaust that comes in a circle. We used that to get the perfect bend off the Rear Pre-Cat. Love it when a plan comes together! :cool:

The original exhaust looks the same as a 2001 V6 Escape/tribute. Still butt ugly.

Decided to update this with part #'s. Click on Part # for Link.
Don't ask me for prices or labor.
This is a custom application with my design as I actually picked the Y-pipe. Also upgraded to 2.5" Magnaflow Cat as stock is 2.25" which now matches the piping.

2 Exhaust Gaskets from Mazda Canada: # AJ19-40-305 (didn’t use, welded right to bracket).
1 short Y-Pipce crossover dual 2” to 2.5” Vibrant # 10355
1 short piece 2” Stainless Steel Exhaust Pipe Flex Pipe Assy like Walker 51025
1 short piece of 2.5" Exhaust Flex Pipe
4 feet 2” Stainless Steel Exhaust Pipe Rigid
3 feet 2.5” Stainless Steel Exhaust Pipe Rigid
1 2.5” Magnaflow Hi Flow Catalytic Converter # 94106 This Aluminized Cat lasted 5 years and now I'm putting on 99206HM Stainless Steel Round Cat.
3 2.5” Slotted Clamps
1 2” 180 degree U-Bend Vibrant # 2624 with 2” Centreline (used right after the pre-cat for a smooth mandrel bend).
MazdaSpeed Cat Back Exhaust for Mazda 6, got from Mazda Dealer.

http://i1049.photobucket.com/albums/...rant-10350.jpg
http://i1049.photobucket.com/albums/...24_2inBend.jpg
http://i1049.photobucket.com/albums/...naflow_cat.jpg
http://i1049.photobucket.com/albums/...DJ/99206HM.jpg

DAFUQ??!! I am a such a (mechanically inclined) noob .. but even I can see that this job doesn't look right!! Thanks for sharing your insight and experience.

2012 CX9. Awesome exhaust design too.

At least it's pointing the right direction, not just coming to a "T". I believe they did it that way for better clearance at the crossmember (just like mine). 1 pipe going by crossmember is better than 2 for clearance. What I don't like about the CX-9 one is the long bendy route close to oil pan. Looks like they had to modify oil pan for exhaust. Guess they like warm oil. I think they need to work on that crossmember to allow 2 pipes there or at least have them join there. The first bit of that pipe also looks narrow then goes wider. Looks like a slow learning curve for Mazda.

CX-9 pic enlarged:

https://www.mazdaforum.com/forum/att...4-09.02.06.jpg