Will your Stainless Works Headers throw a check engine light (CEL)?

This is a very common question that we get asked when someone wants to install long tube headers on their vehicle. Before we go into the full explanation, we can definitely say that not every car is exactly the same. Some people will throw a CEL with our headers, and some people will not.

The main reason is the rear O2 sensors will throw a cat efficiency code. Basically because the high flow cats flow a lot better than the factory cats, the O2 sensor is sensing more emissions than before and they will freak out. The way you fix that issue is you tune out the rear O2s. There are hand held programmers that can do this for you or you can contact your local tuner or contact Stainless Works for a recommendation. This cat efficiency code is most common.

The second reason a CEL will come on is because of the front O2 sensors. The front O2 sensors are meant to reach a certain temperature reading in a certain amount of time. If it doesn't reach that temperature, then it will throw a code. The O2 sensor bung is located in the collector of the long tube header. Where the location is positioned farther away than where the O2 bung is from the factory. From the extra flow of the long tube, the new location of the O2 bung, does not heat up as fast or as much as factory manifolds/lead pipes. This code will definitely require a custom tune to allow the computer to accept this new reading.

With this said, we would like to re-iterate that not every vehicle is the same. Some may install the full system and never have a code thrown. We hope this is true for everyone, but I would not count on it 100%. If you're thinking about installing long tubes headers, you are most likely throwing around the idea of a tune as well. If not, you should definitely consider it. The long tubes and tune go hand in hand and will maximize the most power and efficiency out of your vehicle.

Stainless Works Catback Exhaust Systems do not effect the check engine light and they will not affect your local emissions testing.

If you have any further questions in regards to this, please contact us or contact your local tuner.


What is the difference between mandrel bent and pressure bent? What does CNC mean?

Most factory exhaust systems built through the 70’s were pressure bent. Pressure bending is the process where a tube is placed into a die and a hydraulic ram, which has the other half of the die, or the shoe, is then clamped together to push the tube around the radius. Nothing is inside the tube to prevent the tube from collapsing or buckling, and the machine is completely manual- the operator indexes the pipe by hand according to an angle gauge in the end of the pipe. Not a very precise method of bending, but quick and inexpensive.

Mandrel bending is a process, usually Computer Numerically Controlled (CNC) whereby a mandrel with flexible balls is inserted into the tube during bending. These balls are positioned and pulled through the tube so that the bends are not deformed and maintain a close to perfect shape throughout the length of the bend. The pros are that the tube can be bent on a much tighter radius and still flow well due to the tube being round and not collapsed. The machinery is expensive for a good quality CNC mandrel bender with the appropriate tooling.

CNC bending utilizes a computer controlled set of motors to move the head of the machine and controls the position of the tube and the rotation of one bend in relation to another. After selecting the proper program, the tube is cut to the appropriate length, inserted in the collet, and the button is pressed to start the cycle. The operator does not touch the part until all the bends are complete. CNC mandrel bending is the best method for producing exhaust systems that flow and fit well. With a CNC mandrel bender, you can also bend thin wall tubing so that it weighs less. Being stainless steel, it will not corrode so thin wall tubing is not a concern for durability.

Stainless Works has multiple CNC mandrel tube benders.


Why is stainless steel better than other materials for exhaust systems?

stainless steel is an excellent choice for exhaust systems due to its corrosion resistance. Starting in the early 90’s all OEM manufacturers went to 409 stainless steel for the increased durability and corrosion resistance-the EPA mandated that exhaust/emissions systems be warranted for 5 years minimum. 304 stainless steel, specifically, the Everlast grade that Stainless Works uses exclusively, will not rust or corrode over time (unless exposed to excessive amounts of road salt). Unlike aluminized steel, it will not rust from the inside out due to the corrosive fluids produced during combustion. All of Stainless Works 304 Everlast systems have a lifetime guarantee against defects in materials and workmanship.


What is the difference between grades of stainless steel (304, 321, 409…..?)

409 SS is what is typically used on OEM applications. It has fair corrosion resistance, is magnetic due to its lower corrosion resistance and is a less expensive material than 304. 409 is not an ideal material for a performance/restoration exhaust system because it will turn color (brownish/rust) from being exposed to the atmosphere without ever being run. For OEM’s who never care what the exhaust system looks like, it is a decent material that will last long enough to get past the warranty period. 304 stainless steel has much better corrosion resistance and because of the higher nickel and chromium content. 304 will not turn color from sitting exposed to the atmosphere, and will discolor slightly from getting extremely hot. The best benefit to 304 is that you can maintain it with a scotch bright pad if you ever spill oil on it or have it discolor. Stainless Works exclusively uses 304 stainless steel, made in the U.S.A.


Does stainless steel expand a lot more than aluminized steel? I have heard that a stainless steel system will grow 1 ½” in length when it gets hot. Is this true?

In a word, NO! If stainless steel systems expanded as much as some tall tales would lead you to believe, then how can so many OEMs use it and not have problems? The key is to look at a property of the material called the coefficient of thermal expansion (COTE-Geek terms for how much the material will grow when it gets hot). 

For mild steel the COTE is: 6.3" X 10-6

For stainless steel, the COTE is: 9.4" X 10-6

So, to calculate the change in length we use the following formula:

=(COTE)(Length of component)(change in temperature - Fahrenheit)

Looking at an exhaust system that is 84 inches long, and whose temperature will change 600 degrees F, on average,

For mild steel, change in length=.3157 inch.

For stainless steel, change in length =.473 inch

The difference is about 49% more grown in the Stainless Steel exhaust. However most exhausts made in the past 30 years have been from a low grade of SS, so the difference in COTE is negligible.


What core material do your mufflers use? Do they get louder over time?

Stainless Works uses stainless wool for all of our mufflers. Our mufflers are made from 304 stainless steel, that includes the shells, packing, and cores, and like every Stainless Works stainless steel standard product have a lifetime guarantee. The wool does not burn or blow out over time like fiberglass or other packing materials.


How do your systems differ from a concours correct factory exhaust system?

Stainless Works prides itself on building systems that fit and perform better than the factory systems. A concours type system will be pressure bent like the original, which impedes flow, and will be routed a little differently than our systems. Our systems are designed to fit and perform perfectly. In most cases we improved on the fit of the factory exhaust system. Being CNC mandrel bent ensures that it will fit well every time.


Will I need to cut or weld my exhaust system to install it?

For vehicle applications from 1997 on, our header and exhaust systems are designed to bolt on without fabrication required. The only exception is that with the several wheelbase configurations on trucks, Stainless Works provides catback tubes requiring trimming for shorter wheelbase configurations. For earlier vehicle systems to fit headers, these systems are designed to be trimmed to fit a variety of aftermarket headers including Stainless Works and ust be made adjustable.

Trimming is easy with a common hacksaw-just trim a little at a time and be very conscientious of how much you are removing. You do not have to weld the system in place, but if you never plan to remove it, a tack at each joint is not a bad idea. We also recommend using high temp RTV in the joints for a leak free seal, and use plenty of never-seize on the clamp bolts. Some of the “Hot Rod” systems we sell do require cutting and welding- see our catalog for details.




If I want to weld my system together in stainless steel, what suggestions do you have?

We sell mufflers, bends, straight tubing, tips, etc- everything you need to configure & weld a system together. For cutting stainless steel, a hacksaw or a chop saw with a fiber blade works well. When using a chop saw, make sure to mount the part in the vise very securely-if you pinch the blade with the part the blade will disintegrate. If you cut with a hacksaw go slowly and try to cut as straight as possible. After cutting, sand the pieces so they fit flush using a belt sander and 80 grit or coarser belts. Welding can be done with either a MIG or TIG. For a mig, use 308L wire and gas specially for stainless steel welding (AGA gas sells this under the name Stain-mix). For tig welding use 308L rod and make sure to get good penetration. It is usually a good idea to tack everything together under the car and final weld it on a bench to get good weld coverage all around. Remember when either tacking or welding on your vehicle, be sure to disconnect your battery first!


What type of muffler core do you use?

We make our own muffler core material in house. We own a machine which punches spiral louvers in a piece of tube. The spiral louvers direct the sound into the packing and help control noise very well. Straight through hole perforated. tube does not do a lot in the way of lowering the DB level of an exhaust system.


Since the core hangs in the airflow stream, is it restrictive?

We recently did some dyno testing at Wheel to Wheel in Michigan on Mark Stiewlows new 400 CID, 600 HP engine. With S-tube Stainless Works mufflers and complete exhaust system, we were down 1 hp at peak, but made more average torque and horsepower than with no mufflers. With a chambered muffler that is approximately 6 DB quieter than our first muffler, we were down about 15 flywheel HP compared to open headers. For a very quiet, streetable muffler, those numbers are excellent!! In Marks words, “I would trade 6DB for 15 HP any day of the week. I have had other exhausts that were so loud you couldn’t hear yourself think. These make great power and sound excellent!” Obviously, the tales of perforated cores flowing 50% less than other cores is not true!!


Will polished stainless steel turn color?

It depends on how hot you get the exhaust. On a recently built street rod, the owner put several thousand miles on it and the pipes turned a champagne color. We have had headers turn dark gold when the motor was not timed and/or tuned properly. The nice thing about stainless steel is that is it ever does discolor, you can renew the luster with Blue-Away and Simi chrome polish. Unlike chrome, it will not permanently discolor.


What is the difference between Round Tube & Pipe?

Although most people refer to their exhaust components as "pipe," exhausts are made mostly from round tubing. The simplest explanation is that round pipe is designed for higher pressure applications and round tube is designed more for flow applications. Pipe sizing is defined as a close approximation of the I.D. (inside diameter) with a schedule term for strength or wall thickness, (e.g. Schedule 10, 40, 80...). Tubing is defined by the O.D. (outside diameter) along with a wall thickness (e.g. 18 gage - .049" wall, 16 gage - .065 wall). Stainless Works uses 304 Stainless Steel tubing for all of our SS tubular products.