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Login to post Forums » Grassroots Motorsports » Miata Exhaust: Adding an O2 Sensor Bung

Jan. 6, 2009 12:22 p.m. Woody Dork

I have a Spec Miata exhaust that I bought through Mazdaspeed. It has no provision for the after-cat O2 sensor, so I just bolted it to the underside of the floorpan in the fresh air as a temporary solution.

The exhaust is stainless and made by Borla. I sent them an e-mail asking what type of stainless they use so I can buy an appropriate bung to weld in. They said that the pipe is T-304, but they use mild steel bungs when they put them in.

The price difference between stainless and mild steel is negligible. Is there any reason NOT to use a stainless bung? I'm guessing that Borla uses mild steel because of the cost savings that they would see on a large scale.
Jan. 6, 2009 12:34 p.m. Monkeywrench New Reader

Bosal makes that exhaust, not Borla.
Jan. 6, 2009 12:39 p.m. Woody Dork

It's listed as a Borla on the Mazdaspeed site.
Jan. 6, 2009 12:44 p.m. Monkeywrench New Reader

Woody wrote: I'll have to take another look. I'm fairly certain that it's a Borla. I bought it in '05.

If this is the $150 all stainless cat-back they sell as the "Spec Miata" exhaust, then it's Bosal . Bosal also makes all the exhausts for the Mazdaspeed line of cars.

For anyone who's a Mazdaspeed member and looking for a cat-back, it's the only way to go. With a cat it's not loud at all, and has a real nice deep smooth sound once warmed up. It has gotten a lot of compliments from my non-car friends.
Jan. 6, 2009 12:47 p.m. Woody Dork

Either way, I still need to mount the O2 sensor to it.
Jan. 6, 2009 1:02 p.m. Dr. Hess SuperDork

Use the stainless bung. I buy them from DIYAutoTune.com.

Sure, there's a reason not to use the stainless bung. Suppose you want to screw an O2 sensor in there and never be able to get it out? How you gonna do that with a stainless one?
Jan. 6, 2009 1:10 p.m. RXBeetle New Reader

I weld them with a dead O2 sensor screwed into the bung to help manage heat and reduce distortion. Try not to weld deep or you risk melting threads. After the bung is welded and cooled I run the old O2 sensor in and out a few times with lots of anti-seize for easy instillation of the good sensor.
Jan. 6, 2009 1:26 p.m. Dr. Hess SuperDork

You can also run a spark plug thread chaser in the hole. All the auto parts stores carry one with two threads. It's the big one. 18x1.5 if I recall. I have a tap that size because I've made my own bungs before.
Jan. 6, 2009 1:42 p.m. gamby SuperDork

Woody wrote: bung

huh huh huh heh uhhhhhh huh heh

(sorry )
Jan. 6, 2009 1:53 p.m. Woody Dork

I knew that was coming...
Jan. 6, 2009 1:53 p.m. Keith SuperDork

What do you put in a bung that you're not using? A bung plug, of course.
Jan. 6, 2009 2:16 p.m. Woody Dork

Keith wrote:

What do you put in a bung that you're not using? A bung plug, of course.
March 10, 2009 6:44 p.m. Woody Dork

Monkeywrench wrote:

Woody wrote: I'll have to take another look. I'm fairly certain that it's a Borla. I bought it in '05.

If this is the $150 all stainless cat-back they sell as the "Spec Miata" exhaust, then it's Bosal . Bosal also makes all the exhausts for the Mazdaspeed line of cars.

For anyone who's a Mazdaspeed member and looking for a cat-back, it's the only way to go. With a cat it's not loud at all, and has a real nice deep smooth sound once warmed up. It has gotten a lot of compliments from my non-car friends.

Resurrecting an old thread here...

I finally removed the exhaust last week and had a stainless steel bung TIG'd in place. Monkeywrench was right, it is a Borla. My mistake.
March 10, 2009 7:05 p.m. Type Q HalfDork

Monkeywrench wrote:

Woody wrote: I'll have to take another look. I'm fairly certain that it's a Borla. I bought it in '05.

If this is the $150 all stainless cat-back they sell as the "Spec Miata" exhaust, then it's Bosal . Bosal also makes all the exhausts for the Mazdaspeed line of cars.

For anyone who's a Mazdaspeed member and looking for a cat-back, it's the only way to go. With a cat it's not loud at all, and has a real nice deep smooth sound once warmed up. It has gotten a lot of compliments from my non-car friends.

I would disagree with you there. My Miata had a Mazdaspeed Spec Miata exhaust with a cat on it when I bought it. It was so loud I was setting off my neighbors car alarms when cruising around at 25 mph in 3rd gear. It was the first thing I changed on the car.

Perhaps they have changed the design since then.

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