I need some exhaust tubing fabricated for my rx7 and have a question on the necessary wall thickness. From searching around on the forum, most people recommend 0.125" thickness stainless or mild steel. A local exhaust shop near me uses galvanized iron with the maximum thickness of 16 gauge which is half of what most people recommend. The material they use also concerns me since zinc, which is the material typically used in the galvanization process, has a pretty low melting temperature.

The tubing will go after a header and presilencer to a borla muffler. Since its after a presilencer, the temperatures might be a little cooler, but I'm not sure if it should still be a concern. Are the materials the exhaust shop near me sufficient for my application, or should I look into buying my own exhaust tubing to meet specifications and taking it to the shop?

 

Um nobody would use galvanized pipe unless they were kinda dumb. Exhaust shops wouldn't be able to weld it due to toxic fumes. Osha would have kittens.

I think what you're talking about is aluminized steel. It is easily crush bent, cut and welded at muffler shops. It is always 1/16" and is too thin for a rotary. It will sound tinny and bad because lots of noise will actually leak through the pipe wall.

What you want is 1/8" or .120" like you've searched and discovered (good for you). You could buy the proper thickness mild steel tubing from Racing Beat or a closer metal shop to you, but the muffler shop will not want to cut it and they will definitely NOT be able to bend it.

You're left with the only option of buying some U-bends (from Racing Beat that are mandrel bent for proper flow) and some straight pipe and cutting the pieces yourself with a hack saw or power tools. Then tacking it together with a cheap welder. Then you could take the tacked pieces to a shop to have them fully welded. Or just do all the welding yourself like I've learned to do with my crappy flux core welder.

Once it's all done, you're going to want to paint it with a high temp exhaust paint to prevent rust (remember it's mild steel). If your intake is not too rich, the pipes will stay whatever color you paint them. I like black and it holds up well, even with a supercharger so far.

Oh and don't worry about the exhaust temps entering the Borla. They seem to hold up better to the rotary's hot breath than many other aftermarket mufflers.

 

Thanks for the quick reply. Yeah, when they told me they used galvanized iron I thought it was kinda weird. They probably meant something else. Maybe this would be a good time to pick up a welder and learn how to weld since I've always wanted to. Just as a convenience factor, it would have been nice to just take it someplace and have it done in a couple days.

 

Actually a typical muffler shop can bang out a real cheap exhaust system in a couple hours. It might sound *ok on a V8, but will sound aweful on a rotary.

*ok as in if you like the V8 rumble and are ok with a raspy tone instead of a smooth tuned tone one can only get out of a decent system.

 

On a related note: Does anyone know where I can buy 2.25" OD thick wall tubing? Racingbeat and mazdatrix both carry 2" and 2.5" but not the in between. I wanted to go slightly larger than stock in case I wanted to go with a street port later but I think 2.5" would be too large (plus I already have the muffler purchased). 14 gauge seems to be largest I can find anywhere else. I talked to racingbeat and they are going to get back to me but I wanted to see what anyone else has done.
Thanks

 

I've resigned myself to either using 2" on a 2 rotor or 2.5" on a 3 rotor.

 

You can find the material at a local steel supply house.

You want to ask for Round, ERW, Mild Steel tube. They come in 20 Foot random lengths normally. Some places will sell you a smaller piece.

Metal Supermarkets is at the 285/85 split and is a good place to start. They will sell you a short piece. There is also one in Marietta.

You are going to find out it is not cheap. Steel prices have risen 3 times in the past year.

-billy

 

Metal supermarkets looks like the answer. Thanks for the info Billy. I've heard good stuff about your products so hopefully I'll be able to send you some business one day.

Thanks again for your help Jeff.