Furnace brazed.

Induction hardened.

Shot peened.

These are phrases you’ll find throughout your Summit Racing catalog. They are often included as beneficial selling points on parts—in most cases, critical engine and vehicle performance parts. But do you know what these phrases mean? And more importantly, do you know what they mean to the performance of your vehicle?

We’ve identified seven terms that are casually mentioned in common car part descriptions and briefly explained what each means. In most cases, these are manufacturing processes that are used to make performance parts better. We’ll likely go into greater detail on each in later posts, but for now here are seven aftermarket mysteries explained:

Shot Peening

What it is: According to Engineered Abrasives, a manufacturer of shot peening and blasting equipment, shot peening is a cold work process in which small spherical shot bombards the surface of the part to be finished. The shot acts like a peen hammer, indenting or dimpling the surface. As the media continues to strike the part, it forms multiple overlapping dimples throughout the metal surface being treated. The material surrounding these dimples tries to restore its original shape, causing a continuous layer of compression stress on the surface of the part.

Advantages: The surface compression stress strengthens the metal, ensuring that the finished part will resist fatigue failures, corrosion fatigue and cracking, and galling and erosion from cavitation. It can also improve wear characteristics, straighten out distortions, and texture surfaces. The bottom line in the car parts universe is that shot peening allows for lighter-weight parts with greater fatigue resistance.

Common Uses: Connecting rods, crankshafts, ring and pinion gears.

parts getting shot peened in a blasting cabinet
(Image/mari1408 – stock.adobe.com)


What it is: Magnafluxing, formally known as Magnetic particle Inspection (MPI), is a process for detecting surface and some subsurface abnormalities in ferromagnetic materials such as iron, nickel, cobalt, and some of their alloys. The process puts a magnetic field into the part via direct magnetization or indirect magnetization (we’ll touch on the difference in a later post).

Once the magnetic field is applied, north and south poles are created at each side of the part—just like a standard magnet. The part is then dusted with very fine ferrous particles, usually iron oxide. If there is an interruption, or crack, on the surface of the part, new pole ends will be created on each side of the crack, causing the iron dust to pile up on each side of the crack.

Advantages: Magnafluxing makes it possible to detect cracks or stresses in parts that are not necessarily visible to the naked eye.

Common Uses:  Engine blocks, crankshafts, cylinder heads, pistons

Furnace Brazing

What it is: Brazing is a metal-joining process whereby a filler metal is heated above melting point and distributed between two or more close-fitting parts by capillary action. The filler metal is brought slightly above its melting temperature while protected by a suitable atmosphere, usually a flux. It then flows over the base metal (known as wetting) and is then cooled to join the workpieces together. It is similar to soldering, except the temperatures used to melt the filler metal are higher for brazing.

According to Bodycote, a leading supplier of thermal processing services, there are four different types of furnaces used for brazing: vacuum, controlled atmosphere, continuous, and reducing atmosphere. One of the most common forms is vacuum brazing. In this process, the parts to be joined are cleaned, brazing filler metal is applied to the surfaces to be joined, and then the entired assembly is placed into the furnace. The unit is then brought to brazing temperature after the furnace has been evacuated of air. This eliminates any oxidation or contamination occurring as the braze filler metal melts and flows into the joints.

Advantages: Furnace brazing offers high integrity joins but is cost-effective to help keep the price of parts down.  In addition, this process allows the joining of unweldable, dissimilar, and non-metallic materials.

Common Uses: Radiators

Black Oxide

What it is: Black oxide is a conversion coating for ferrous materials, stainless steel, copper, zinc, and more. It is formed by a chemical reaction with the iron in metal, which produces a magnitite (Fe3 O4) on the actual part surface. This creates a protective coating which is an integral part of the metal component itself. As a result, black oxide does not affect the dimension, hardness, temper, or surface properties of the part.

So what are the advantages?

Advantages: For all intents and purposes, black oxiding retains the original dimensions of the part and adds no weight. It has superior anti-galling properties and also provides a nice decorative finish to many parts (especially when treated with the hot black oxide process which creates little color variation from part to part). Depending on the post-treatment, black oxide treatment can also offer great corrosion protection.

Common Uses: Fasteners and hardware, seat brackets

Heat Treating

What it is: According to Mid-South Metallurgical, heat treating is the process of heating or cooling metals to alter their physical or chemical properties without affecting size and shape. The process for heat treating includes heat the part to a certain temperature, maintaining the elevated temperature for a specific duration, and then quickly cooling the metal back to room temperature. Choosing the right type of quenching liquid to quickly cool the part is essential to avoid cracking. These liquids can include brine, liquid salts, and various oils.

Specific heat treating processes vary depending on the type of metal being used and the intended strength of the treated part. Furnace temperature has the most significant impact on the results of heat treatment, with some parts requiring temperatures up to 2,375 degrees F and others needing temperatures as low as -120 degrees F. Heat treating results are also sometimes dependent on heating rate, with some heating processes requiring rapid or slow heating.

Advantages: The goal of heat treating is to create a heat-‘treated part strong enough to perform a special task.

Common uses: Axles, pushrods, camshafts, tools, connecting rods

Induction Hardening

What it is: Induction hardening is a form of heat treatment in which a metal part is heated by induction heating and then quenched. The process for induction hardening is based around the principle of electromagnetic induction in which an alternating magnetic field is created within the part. This causes with outer surface of the part to heat without affecting its core. Induction hardening is used to selectively harden areas of a part or assembly without affecting the properties of the part as a whole.

Advantages: Inducting hardening offers increased fatigue strength by surrounding a soft component core with a hard surface area. That makes it ideal for parts that experience torsional loading.

Common uses: Axle shafts, cam lobes, suspension components, gears, engine components

Sonic Testing

What it is: Sonic testing involves the use of sound waves to check dimensional consistency of metal.  In this process, electronically generated sound waves are sent into the metal through a probe, and reflected back to the probe by the metal. The time it takes for the sound waves to get back is measured and then electronically converted to a dimension. This type of testing is ideal for checking thicknesses in areas inaccessible to conventional measuring equipment—the cylinder walls of an engine, for example.

Advantages: Sonic testing allows you to locate potential weak spots within engine blocks, particularly in the cylinder walls. That will prevent you from buying an old junkyard engine that’s prone to cracks, or overboring a block that doesn’t have cylinder wall material to spare. Sonic testing is completely non-destructive—components don’t need to be cut or sectioned.

Common Uses: Engine blocks

Author: David Fuller

David Fuller is OnAllCylinders' managing editor. During his 20-year career in the auto industry, he has covered a variety of races, shows, and industry events and has authored articles for multiple magazines. He has also partnered with mainstream and trade publications on a wide range of editorial projects. In 2012, he helped establish OnAllCylinders, where he enjoys covering all facets of hot rodding and racing.