Magnaflow Exhaust- through bumper

turbochad · 01:12 PM

I thought it would be interesting to share this project with the community.

I originally wanted a GT3 style M&K exhaust for my '86 Carrera, but I enjoy mild fabrication and wanted to try developing something myself. I spent some time on the exhaust clip thread listening to the the different muffler sounds and characteristics and settled on a Magnaflow 1 in 2 out style. I wanted to keep a cat on the car because it is my daily driver but clearly the stock cat was old and too restrictive.

I settled on a design and got to ordering. I ordered a Magnaflow high flow cat (metallic), a 1 in 2 out SS Magnaflow muffler, a 2.5" 304 SS U bend, two 2.5" SS 3 bolt flanges, a SS O2 bung and a 2.5" 321 U bend from Burns Stainless. I later ordered a couple of large band clamps from McMaster-Carr, but not until I had the muffler in place and could measure the strap circumference.

I didn't want to use the stock outlet location combined with the second out on the other side, the center out (GT3 style) didn't naturally make sense because of the muffler style so I came up with the idea of going through the bumper (Carrera GT style). Lots of turbo track cars have holes drilled in the bumper but I haven't seen any done with the exhaust exit there. This orientation uses very little tubing after the cat. The whole setup is also very light compared to the stock cat and muffler.

I was a bit nervous that I would be cutting up a perfectly good bumper and ending up disappointed, but it turned out nicely. There is plenty of room in there for the muffler, the muffler body is angled so that the tips come out level with the openings, the straps fit around the factory brackets and it is all tucked up nicely with nothing hanging below the valance. I had to get a set of euro bumperettes (darn), and then fabricate the trim rings for the opening. I put some aluminum mesh in the trim grills to make it all look clean and tidy, and got a full valance from RarelyL8 that fills in the stock outlet. I need to trim the driver's side lower bumper end, paint the new valance and bumper ends to finish the project.

I am happy with how it turned out, it looks good, sounds good, and power is up as well. It is not as loud as I thought it would be, and it is plenty quiet for a daily driver. The sound is deep down low and mean up top. It also has a nice deceleration burble that really sounds nice. I'll take some better pictures of the whole car and some underbody shots if anyone is interested in how it all looks underneath.
Cheers,
Chad

tobluforu · tobluforu's Garage

That is pretty cool looking!

mholbrook38 · mholbrook38's Garage

Very nice. Can you post up additional pictures. And a list of parts required.

Oh Haha · 01:20 PM

Sweet!!! Nice job on fabbing that setup.

Eddie Bello did something similar with his 2xturbo exhaust.

BTW-get ready for this thread to become epic quickly.

SpeedracerIndy · 10-31-2010, 01:18 PM

That looks great! If this had been an option when I bought my M&K setup last year I would have paid extra for it. How did you create the area surrounding the pipes? Looks like it was meant to be there.

I would love to see some pictures from underneath to see how the plumbing looks.

Brad394 · Brad394's Garage

I like it ...

very nice look

BG

Hotwatermusic · 10-31-2010, 01:32 PM

Damn, that is freaking cool.

brcorp · brcorp's Garage

Nice!!

turbochad · 10-31-2010, 03:07 PM

Here are a few more pics that should show how I approached the design. Also here is a short list of parts I used in the build.

From Summit:
(1) MPE- 12265 Magnaflow Muffler
(1) MPE-59926 Catalytic Converter
(1) WLK-42432 Dynomax Pipe
(1) SUM-G2990SS O2 Bung

From Burns
UB-250-40-16-321 (321 U pipe for tips)

From McMaster-Carr
(1) 5276K42 Constant Tension Tbolt hose clamp
(1) 5276K43 Constant Tension Tbolt hose clamp

From Verocious Motorsports (I found online)
(2) 3-Bolt 304 SS Vibrant Exhaust Flange

From our Host
New exhaust gaskets and copper M6 12mm exhaust nuts

From RarelyL8
Carrera uncut fiberglass rear bumper valance

From MetroMods (ebay)
UNIVERSAL BLACK ALUMINUM MESH GRILLE GRILL 12" X 48"

I used the stock cat pipe collector, cut it off the stock cat and welded on a short piece of straight 304SS tubing that was flared to accept an inserted tube. I had this piece from another project. Then came the new cat fitted to the new flange. I fabbed this in place with the stock muffler acting as a jig so the flange would be in the correct location. Then I removed the stock muffler and began working on the new muffler.

On the muffler I used the 321 SS tubing for the outlets since they would be visible 321 turns a nice gold color when heat cycled. I used SS wire in my MIG to keep it all in the family. I had to cut the outlet flanges off the muffler body because you have to make a tight 90deg turn to keep the tips inside the bumperettes.

The trim rings I made out of 1"x1/8" steel strap. I cold formed it around a gas cylinder safety cap that I tack welded to my welding bench (4" OD). I welded a tab on the license plate side to attach the trim rings to the bumper. The mesh is held on the back of the grill with epoxy. I cut the holes in the bumper with a jig saw (very carefully) and protected the paint with masking tape. I cleaned up the cuts and did the final fitting with an pneumatic rotary deburring tool.

All in it took a full day of disassembly, fabbing, and final detailing, and I am still not finished with the paint work on the lower valance, and I haven't installed the seal between the bumper and valance yet (waiting on paint).

turbochad · 10-31-2010, 03:15 PM

Quote:

Originally Posted by Oh Haha

Sweet!!! Nice job on fabbing that setup.

Eddie Bello did something similar with his 2xturbo exhaust.

BTW-get ready for this thread to become epic quickly.

I bet it would look really cool on a turbo

. Any pics of Eddie's car?

911pcars · 10-31-2010, 03:18 PM

Looks like a nice clean project. Congratulations.

However, I don't see a shield between the converter and the engine. You realize it gets overly warm down there. I suggest fabbing something to take the place of the factory cat shield.

MHO,
Sherwood

turbochad · 10-31-2010, 03:37 PM

Quote:

Originally Posted by 911pcars

Looks like a nice clean project. Congratulations.

However, I don't see a shield between the converter and the engine. You realize it gets overly warm down there. I suggest fabbing something to take the place of the factory cat shield.

MHO,
Sherwood

I was thinking about the purpose of stock shield as I was doing this, maybe incorrectly. It seemed to me that the stock shield isn't designed to protect the engine from the cat's heat since the shield sits under the cat and not between the cat and the engine. I was thinking that the stock shield is designed to protect the rear tire from the cat's heat and keep heat in the cat from being lost to passing air under the car. The hotter the cat, the better the emissions. It always seemed strange to me that the cat heat shield is more of a skid plate.

The new cat is smaller than the stock one and is now a ways away from the rear tires. there is enough clearance to do a valve adjustment without removing the cat pipe. A heat shield is probably a good idea regardless. A couple of tabs and a curved piece of sheet aluminum should do it.

ShakinJoe · 10-31-2010, 03:44 PM

Very creative. I will guess there will be copiers of this idea. It really tucks the exhaust up in there and looks great!

turbochad · 10-31-2010, 03:59 PM

It would look really cool on a car without bumperettes or with an IROC bumper too. I wanted the bumperettes for my daily driver, but I considered leaving them off and filling the remaining hole. You can also do this with a 2 in 2 out utilizing headers or SSIs.

911pcars · 10-31-2010, 04:20 PM

Quote:

Originally Posted by turbochad

I was thinking about the purpose of stock shield as I was doing this, maybe incorrectly. It seemed to me that the stock shield isn't designed to protect the engine from the cat's heat since the shield sits under the cat and not between the cat and the engine. I was thinking that the stock shield is designed to protect the rear tire from the cat's heat and keep heat in the cat from being lost to passing air under the car. The hotter the cat, the better the emissions. It always seemed strange to me that the cat heat shield is more of a skid plate.

The new cat is smaller than the stock one and is now a ways away from the rear tires. there is enough clearance to do a valve adjustment without removing the cat pipe. A heat shield is probably a good idea regardless. A couple of tabs and a curved piece of sheet aluminum should do it.

Exactly. PAG left out the engine shield. They were more concerned with burning the LR tire and setting dry grass on fire than the engine soaking more heat from the cat. Operating temp of a typical cat under normal conditions is about 900-1500ºF.

Sherwood

RarlyL8 · RarlyL8's Garage

Man that is awesome!
Looks like I better make some more valances ...

Zeke · 10-31-2010, 04:29 PM

I think you are understating the amount of work you did on the trim rings. That's the interesting part to the whole design.

Believe it or not, I think I would have painted that whole business white. Nevertheless, from an ex fabricator to another, you did an outstanding job.

(PS, a deep silver pewter color on the exhaust grills/trim would have been interesting too.)

tcar · 04:46 PM

A couple of us did a drive up into the mountains with Chad this morning.

(Incredibly beautiful fall day here today... check out the pic in the park...)

I thought it would be very, very loud, as many 2-out mufflers are; but it's NOT.
It's a nice, low mellow sound. It sounds great at high RPM in the tunnels, too.

I can't tell you enough the quality of the work, very professional looking, polished and well-thought-out.

I like the black with the bumpers, trim, etc.; cohesive.

Just a fabulous job, from design through execution.

BTW, I've understood the 'heat shield' to be mostly to protect the cat from grass, etc. if one drives/parks on flammable vegetation.

Also, someone makes an aftermarket heat shield that bolts to the lower valve cover on the L side; a standoff. I can't find the name of the mfg at the moment. Porsche never used one.

Oh Haha · 10-31-2010, 05:11 PM

Quote:

Originally Posted by turbochad

I bet it would look really cool on a turbo

. Any pics of Eddie's car?

If you can, check out the shots from his Excellence feature. I could only find this video right now.

223 MPH Video

911pcars · 10-31-2010, 05:42 PM

Quote:

Originally Posted by tcar

A couple of us did a drive up into the mountains with Chad this morning.

(Incredibly beautiful fall day here today... check out the pic in the park...)

I thought it would be very, very loud, as many 2-out mufflers are; but it's NOT.
It's a nice, low mellow sound. It sounds great at high RPM in the tunnels, too.

I can't tell you enough the quality of the work, very professional looking, polished and well-thought-out.

I like the black with the bumpers, trim, etc.; cohesive.

Just a fabulous job, from design through execution.

BTW, I've understood the 'heat shield' to be mostly to protect the cat from grass, etc. if one drives/parks on flammable vegetation.

Also, someone makes an aftermarket heat shield that bolts to the lower valve cover on the L side; a standoff. I can't find the name of the mfg at the moment. Porsche never used one.

GT2 heat shield (Porsche MotorSports race engine):

From B. Anderson's High Performance book:

We used to make them (HeetSheets). Now out of production.

Sherwood