I just picked up the car from Flatout Motorsports after having a new custom mid-pipe welded up.

Here is the HJS cat. I saved a few bucks by buying it without the cones / transition pieces, so those were welded on at the shop.



Behind the cat are two Coast Fabrication mufflers. The first is packed with extreme temperature stainless steel mesh. The second smaller muffler is packed with slightly less beefy stainless steel "scrubble".

The second muffler is actually where the flange connecting the mid-pipe to the cat-back would normally sit. Removing that flange makes it a true 3" system, and it was a convenient place to put the second muffler.



You can see in the pictures that mufflers are clamped on rather than welded, which was the recommendation I received from Coast Fabrication. Among other things, this allows the mufflers to be removed with the exhaust still on the car if they should ever need to be repacked.

Here you can see what it looks like installed on the car. The second muffler is right where the flange would normally sit. This required cutting off about a foot of pipe from the Borla cat-back and relocating the hanger.



Here is a view from the side showing the ground clearance was not sacrificed:



Here are some close-up pictures of the welds. Flatout Motorsports did a simply awesome job putting this together.







There is also an inconel heat shield installed on the cat, but unfortunately I did not think to snap any pictures.

So, despite being way over-budget already, I couldn't help but have them strap the car to the dyno for a few before and after pulls.



The numbers are a bit on the low side, but the shape of the graph looks good, and the horsepower gain (+14.6) is awesome.

The sound is very different than before, despite keeping the same cat-back (Borla). It's also noticeably louder inside the cabin, but that is to be expected from the thin-walled Coast Fab mufflers. I'm taking it to an autocross this Sunday, so I'll get some feedback on how it sounds outside the car. I'll also put it to the test against our region's relatively strict sound limits.

Anyway, I've only driven it home from the shop so far, so it's too early to pass any final judgement on tone or volume. The hp gain and weight loss are what I was really looking for, and I am very pleased in that regard.

Sources:

HJS Motorsport -
100 CPSI Catalytic Converter -
http://www.hjsna.com/

Coast Fabrication -
3" x 17" x 4.5" Muffler w/ SS Mesh Packing
3" x 12" x 4.5" Muffler w/ SS Scrubble Packing
http://www.coastfab.com/

Mazdatrix -
Exhaust Flange
http://www.mazdatrix.com/

Mazdaspeed Motorsports Development -
Miscellaneous gaskets and hardware
http://www.mazdaspeeddevelopment.com/

Flatout Motorsports -
Welding, Fabrication, and Dyno
http://www.flatout-motorsports.com/

Kool Mat -
HeatMaster Heat Shield
http://www.koolmat.com/

 

Very nice custom midpipe. Nice gains as well.

 

What year and model is your car?

I hope you say automatic

 

Nice looking installation job! How did the autocross go?

 

this

 

does that look like an auto trans in the pic?

it is probably a bit loud ....

 

dynapack dyno. forget the numbers. look at the gain.

 

The autocross today was a success in regards to the mid-pipe (unfortunately, the car was poorly driven).

I didn't stick around to sneak a peek at the sound logs, but the car was well under the limit of 90 db @ 75 ft. Subjective feedback was the the car sounded great, and was far from the loudest car there. Several people walked up to ask what I had changed on the car and to compliment the new exhaust note.

The increased volume is great for autocross, but a bit loud for the street. Of course, everyone has a different opinion on how loud is "too loud". For the amount of street driving I do, I'm happy with the compromise.

 

Here are a couple pictures of the heat shield. I made a template from poster board and mailed it to Kool Mat in North Carolina. Within a few days, they built me a custom heat shield made from "2500º NASA Insulation sandwiched between two textured inconel panels".

The heat shield matched the template perfectly, and they pre-shaped it into a circle with proper space for an air gap. Overall, top notch product and service.

 

Also, here's a pic of the cat before it was installed. If you stand back far enough, you can see right through it.

 

Looks like a great fab job, the welds look fantastic. If you dont mind me asking, total cost?

 

I have avoided adding up all of the receipts, but it was well north of $100 per horsepower... Don't tell my wife.

 

lolol, i expected as much, especially with the use of the HJS cat.

 

the packed mufflers are going to break down over time but otherwise it looks outstanding, well done!

 

Interesting comment, Laythor. Do you have first-hand experience with the Coast Fabrication mufflers?

 

no first hand knowledge, just years of being here and reading about guys with packed mufflers who have had to replace them after some time.

 

Beautiful work man, congrats. The gains are fantastic.

 

Nice work and writeup, thanks!

 

this was already acknowledged by Coast as a possibility and they have taken that into account for the install recommendations.

 

Thanks Zoom.

Also, not all muffler packing is created equal. Coast Fabrication offer three different options for packing material:
http://www.coastfab.com/images/pdf/M...ermination.pdf

 

sound clips? did I miss them?

 

Polly want a cracker?

For your own education, it just depends on what it is packed with and the style of muffler. Speaking from direct experience, in this particular case it will never be needed.

 

so you can guarantee the packing will never break down?

 

I can guarantee that you aren't a source of good information on the subject.

Why don't you just come out and say what you're really driving at?

 

i realize you live in a world were people are always out to get you and everything has a double meaning. In this case, again, it's unfounded.

that's all I said about this

followed it up with
at no point did I claim to be a source of good information. i simply (but i guess not simply enough for some) pointed out that due to reading these boards I felt the packing would break down over time.

Not really sure what you think I'm driving at but please enlighten me.