Disclaimer: I meant DIY in the sense of "Did it Myself", not "Do it Yourself". This is not a step-by-step guide for anyone else to follow. I am not a professional in this area- I am a self-taught car hobbyist. This is just a thread on what I did to replace my exhaust system for additional performance and sound.


INTRODUCTION

Problem:

The exhaust note on my CTT has always been a little too subdued for my personal tastes. As a car enthusiast, I think exhaust notes can be downright intoxicating. While the CTT wasn't necessarily bad, better than most actually, it just didn't say "I am rocking 600hp + at the crank here buddy...BACK OFF "

I had 70mm (~2.75") Milltek Secondary Bypass Pipes and 70mm Supersprint Race mufflers. The stock diameter is about 2.5"which is slightly smaller than 2.75”. The larger diameter pipe is for better flow, better performance, and better sound. If I connected both of these parts to the factory 2.5" system it would reduce flow in the middle and have unknown consequences to the exhaust velocity with mismatched pipe diameters . This would be a problem if I wanted more than just some sound improvement.


Do you have ADD ? Skip right to the “meat and potatoes” HERE!!


Plan:

After not being satisfied with just a secondary bypass pipes and scoring a sweetheart deal on a used Supersprint Race Exhaust, I decided to throw the kitchen sink at it. Go big or go home, right?

1. First off, I would have to replace the midsection pipe with 2.75” piping to keep consistency from the rear mufflers to the secondary cat bypass pipes. Supersprint sells a 70mm midsection for about $1300 plus shipping. Since I think that is ridiculous, I guess I will have to fabricate my own.
2. Since I do not want excessive drone and annoying loud (straight pipes anyone?), I would add an x-pipe upstream to merge the sound from both engine banks. It also makes the exhaust sound more pleasing to the ear – more melodic. Since I could not source a 2.75” x-pipe for under $250, I will have to make my own. How hard can it be? 
3. Since the stock exhaust clamps will not work, I will need a set of 2.75” 304 SS exhaust clamps that will not deform the system and help deter corrosion.
4. I will have to fabricate a new set of hangers and reuse the stock mounting location and rubber.
5. While I am at it, I should probably remove the stock primary downpipes and remove the primary AND secondary cats for added performance and quicker spool up for the turbos. And to keep the costs at bay, I will remove the stock DPs and install the new ones myself.
6. O2 extenders will have to be used to keep the check engine light off.


Added Value:


1. The new system will let the turbos spool-up faster for less turbo lag and quicker acceleration.
2. The turbos should make about 1-2 psi more of boost on my tune without the cat restriction.
3. It will be a complete “open” exhaust system.
4. The new system will weigh much less without the four cats and the boat-anchor of a rear muffler.
5. I will get a nice “bark” from my CTT when starting her up.

 

THE WORK (aka Meat and Potatoes)


Planning

Note: I already had the Milltek secondary bypass pipes and SuperSprint exhaust, so sorry, no before pics on these goodies.

Primary Downpipe Comparison




Reached out to Rob from Leistung Motorsports for the primary downpipes. He is an absolutely fantastic guy by the way! I do not think I have ever received better customer service from a company. Rob and I worked closely together to work through a few revisions of his primary downpipe bypass pipes that ended up exceeding my expectations. Here are the stock DPs on the far left followed by two early revisions.




Here is the final version (to date). Port matched ½” turbo flange, waterjet mounting tabs, smooth transition from 4.5” to 3” and optional additional AFR bung all in 304 SS glory. Note: this is an unpolished prototype.



Another angle



Wow, sure is smooth..



Pretty slick mounting tabs


Primary Downpipe Weight



Factory Downpipe is kind of chunky at 12 lbs, however, not too bad overall.



New Downpipe weighs in at 7.3 lbs. This was version 2, so I am sure the last version was a little bit under this.

Turbo Housing



View of back of factory turbo housing after factory cat removal. Large housing and small exducer wheel. You cannot see it in the picture, however, the housing is concave in shape. That means that it is critical to port-match replacement downpipe.


Factory System


Factory Primary Downpipe



Good ridden stock cat restriction! Stock weld bead is also another choke point. ¼” intrusion?

Factory Midsection and Muffler



Stock midsection from underneath – View 1



Stock midsection from underneath – View 2



Complete system removed. I did not weigh it since it was awkward, however, it was HEAVY! I am guessing 60 lbs + as removed.


Install and Fabrication


Factory Primary Downpipe Removal/Install



Sorry, I do not have the patience to stop every 20 minutes to take pictures for removal. Besides the fact that my hands are filthy and I have to touch a camera. I CAN tell you that removing the stock cats were a royal PITA. And you will need to create crazy extensions like this to remove each bolt. Each one was like a small mini-challenge in itself. I think I spent atleast 15-30 mins per bolt trying out the right combination of extensions to get it removed.



I had to create a custom tool to remove the mounting tab bolt on the passenger side. Whenever I have to create a custom tool to do a job, it automatically goes to a 9 out of 10 on the difficulty rating. 13mm 12pt closed end wrench, cut to length and shaved for added clearance- in combination with a prybar for leverage, I was able to remove the bolt. I had less than 3 degrees of movement. Removal is NOT DIY friendly. Not recommended for the average or above average Joe. As a disclaimer, I think a long neck ¼” air ratchet with atleast 35 ft lbs of torque would have worked in this location.



Installed – passenger side.



Installed – driver side.

X-Pipe Fabrication



Seems like a good start to me. How am I supposed to know? I have never done before…



Angle 2



Looks like it will work… just got to weld it in this EXACT position. Don’t move.



There we go! Welds leave a little something to be desired since I have to use the spot-welding technique on MIG to prevent burn through. Pressure tested X-Pipe to 10 psi to guarantee no leaks. Another summit conquered!

Midsection Fabrication



Sorry, too busy test fitting each little section under the vehicle to stop and take pictures. Here is an example of positioning bends. Note the light marker on each end to line up both positions when test fitting and grinding down each section for fitment.



Here is the end result after removing the tacked up system for the final work. I ended up placing the X-pipe offset under the vehicle to keep clear access to the center support bushing for the rear cardan shaft. Hence the extra bend on the passenger side from the x-pipe.



MIG welds completed on system on bench. I sure was regretting not getting a TIG welder. Those high disposition welds aren’t too pleasing to the eye. Even though they are structurally sound welds, I will have to do something about this…..



A close up of these MIG welds…



There we go! A little of grinding, ok A LOT of grinding and it is already looking much much better. Take that TIG!



Complete MIG section after grinding session.



Have to create strong custom hangers from 3/8” and ½” 304 SS rods. I think a cutting torch can help with that. By the way, fun tool!



Hmm… looks hot.



Mechanical leverage advantage for the win!



Quick shot of the Supersprint Race mufflers after bracing the two together permanently as one unit with 304 SS bar. Will help to keep down resonating and independent muffler movement. Bracing was done in spots that will not create clearance issues.

Final Results









Shots of new exhaust system after 6 hours of driving over the weekend.



Note how well the exhaust system is tucked underneath the chassis! No clearance issues, no knocking! Perfect.

 

CONCLUSION

Exhaust note is just right for me. Interesting sound.. will try to get video clip. Marginally louder at startup, partial acceleration, and WOT. Exhaust note now “gurgles” on lift off- which is so so so pleasing to hear! No “sound symposer “ for me needed in my A-pillar – I have my panoramic roof open as much as I can to hear that note. Cruising (off boost) is just as quiet as it was before. You can hear the turbos now whistling through the exhaust and the whole exhaust has a “rumbling” sort of noise when driving through the city. If I had to sum it up in one word, "vicious". You know the same noise that says “I have major power under the hood… BACK OFF”

 

great write up Kent! and nice full system!! post some vids! the 3" LMS mid system should be done soon! I'm hoping for a little lower rumble and smoother exhaust note from the balanced system. it'll be interesting to compare the sounds of the two full systems. Any dyno time soon?

 

Not the "prettiest" weld I've seen but who cares, no one looks at the car from bottom up (well, most people dont at least ) Nice!

 

Thanks!!

You are right that TIG welding would be more aesthetically pleasing. For that reason and the fact that you have more control, lower weld deposition, and no need for grinding is why most professionals TIG weld exhaust systems.

The reality is that most people only have an ARC and/or MIG welder as basic shop tools. When MIG welding, its exponentially more difficult to lay down a "pretty" weld on a round surface when it is thin gauge metal without burning through your material. So it is not fair to compare it against a solid lap weld on say 3/8" flat plate. It is just two different animals. The MIG "spot" weld technique exists for situations like this at a penalty of additional grinding.

The only times I feel like I "need" a TIG welder is when welding exhaust systems, rollbars, and aluminum.

Next time, it might be in the budget. For now, I am happy

 

Thanks! Yeah, you are right that I should put up a video. The only rub is that is almost impossible to accurately reproduce the lower freq. range without buying/renting thousand dollar equipment. I have several devices that can record video, however, I do not know which mic will serve me best here. I might try to rent a "GoPro" since they now seem to be the go-to standard for car videos.

Sounds like Rob is working out the kinks in the 3" system. All else being equal, you should make more power with the 3" than the 2.75" I installed. Well, if he is using an open muffler design as well. Not to mention that you will make a little more noise

Debated whether I should put her on a Dyno now or after I upgrade my throttle body. A dyno is a "nice to have" for this car right now. The proof is in the pudding, where I have already shamed many a sports cars in my area. That is enough for me at the end of the day.

 

THAT IS SICK!!!!! Awesome job and kudos for a hella job. Thought of doing it myself as I am not as good with the welder as I would like. Do you have a tube bender at home to bend that clean or did you take it somewhere to get it done?

 

Thanks!!! I do not have a tube bender and did not take it to a local shop (believe it or not, we do not have local "muffler shops").

If you use a pipe bender at home, you would first need to fill the pipe with sand and then cap both ends before bending. The sand stops the pipe from bending in on itself and causes those performance-hampering crinkles.

I opted for a third option, which is to buy a box of pre-bent mandrel bends from the internet. I pretty much got a good mix of 45 deg, 90 deg, 60 deg bends. As well as a and few odd bends (matter of fact, I have a few left over bends I wont be using, let me know if anyone is interested). So putting it together was more like a jigsaw puzzle.

Using this option also allowed me to make sure I was only getting quality bends and quality pipe - 16 gauge 304 SS . It was about $400 in quality bends here.

This system should last a very very long time.

 

I still remember my first time welding aluminum plates using TIG welder. Fun days.

 

Very impressive, and am somewhat jealous you did it yourself. Sounds like some fun "me time". Can't wait to hear the sound clips.

 

Great work, very impressive. I dont have the time or resources to do something like that.

 

Wow that is awesome! I'm a fabricator and engineer myself and can definitely appreicate work like this when I see it! Just to be sure I'm reading and seeing everything correctly.. you took out all the cats in your car and it's basically a open exhaust directly out of the turbo and into the pipes you made.. and then into the supersprint muffler exhaust and out the back correct?

Larry

 

I agree that there is a whole other level of appreciation if you recognize the amount of thought and technical challenges behind a project. Hat tip to you as well

Yes, you got that right. Of course, this is for track use only

 

I'm awaiting my new 2013 CTT that is schedule to be assembled on Sept 25th but.. debating if I should totally delete the primary cat or leave the primary cat and just delete the secondary one.. my decision is.. well less on exhaust.. (yes yes I know it's bad but I have a hybrid to offset my carbon balance hahaha..) but more on the noise.. I will be driving it all the time but I wasn't sure how much louder it is with the primary cats gone and being almost a straight thru exhaust.. I know this is subjective but.. what's your opinion on it? And.. would you drive it long distance like 1000+ miles with the exhaust you currently have?

I would love to build the exhaust myself like you did but.. don't have the time in my day to do it ;(.. I'll probably opt for the Akrapovic full titanium exhaust..

Thanks for your feedback!
Larry