Exhaust Manifold – Steel or Cast Iron?

Heavy Duty Trucks Parts

You have had your truck for many years now and during routine maintenance of your vehicle, you realize that your exhaust manifold is leaking. Let’s say it’s at a point where you can’t repair the leak, which means you have to replace it.

As you are beginning to inquiry about a new exhaust manifold, your parts supplier asks you if you want ‘Cast Iron’ or ‘Steel’. Would you be able to answer this right away? The OEM manifold that was removed from your truck is more than likely cast iron, so why would you be offered a steel version?

Here is some information that can help you make a decision.

Cast Iron

  1. The material is inexpensive and fairly easy to work with. OEM manufacturers tend to use cast iron because of this.
  2. Material is durable and can have a long life span.
  3. It is heavier than steel and can become brittle and prone to cracking under extreme heat cycles and age.
  4. Requires special tooling for production, but is easier for mass production.

Steel:

  1. Steel has different options, mild steel or stainless steel
  2. Mild steel has a ‘low degree to thermal expansion’ and is an excellent choice for flanges.
  3. Stainless steel is stronger and more corrosion resistant than mild steel, and also costs more.
  4. Stainless steel can be prone to expanding during heat cycles, then retracting when cooling. This can rip off the bolts or studs that hold the exhaust system together.
  5. Can be used to make traditional log style exhaust manifold, but is better suited for custom made tubular exhaust manifolds, without special tooling needed.

Steel exhaust manifolds can reduce heat loss, especially stainless steel versions, which can lead to an added increase in horsepower and performance. You can add a ceramic coating to cast iron exhaust manifolds for a small increase, but not as much as you would gain with steel versions, which can also be given a ceramic coating.

The decision to replace your exhaust manifold and what type of replacement to go with can depend on many factors.

  1. How long do you plan to keep the truck?
  2. Do you want increased performance and more horsepower?
  3. What does your budget look like?

Now that you are more informed, you can choose the best option that fits your needs.