A Custom Exhaust System Begins With Quality Exhaust Flanges: A Primer

Exhaust Kit

A solid exhaust system is fundamental to the overall performance and look of your hot rod. Whether you are crafting a custom street rod, hot rod, rat rod or race car, the exhaust system is vital. And the exhaust system begins quite literally with the exhaust flanges commonly referred to as header flanges.  

The Significance of Header Flanges

It’s ok if you no idea what exhaust header flanges are, we will explain. If you have fabricated, or are planning to fabricate your own headers, then you are familiar with what these flanges are. So to make things clear and easy to understand, the beginning is the best place to start. The beginning is a basic explanation of the exhaust system. When your hot rod’s engine is running, the engine is burning fuel to generate power. This is the process of combustion. Combustion produces gases that must be released from the engine, and the exhaust system accomplishes this. Exhaust gases come out of the cylinder head and into a network of metal pipes that carry the gases from the engine to the outside of the hot rod. The primary and most basic parts of an exhaust system are the exhaust manifold/header, exhaust pipes, muffler, and then tailpipe. All of these parts together route the exhaust gases under the car and out the back. So what about the exhaust flanges? Where do they figure in this most basic model of exhaust explanations? To answer this question you only need to focus the discussion on one part of the system, the manifolds. Or rather, the part that a hot rodder replaces a manifold with, which is called a header.

From Manifolds to Headers

Exhaust manifolds and exhaust headers perform the same essential function, which is to funnel and merge exhaust gases from each of the engine cylinders into the exhaust pipes, then to be channeled to the tailpipes and out behind the car. Stock manifolds are commonly made of cast iron and are bolted to the cylinder heads. They are built to be strong, long lasting, fit into tight spaces and easily manufacturable. Because cast iron manifolds have thick walls, they keep heat from seeping to other engine parts and handle the high temperatures well. Exhaust gases coming into the manifold all collect in the corridor-like chamber, then move out into the pipes that are attached to the back the manifold normally at a bolt on flange. But because of the chamber-like design, heated gases can move around inside of the manifold passage which leads to the creation of ‘back pressure”, essentially the exhaust gasses are not being cleared away from the cylinders as fast as possible, which leads to the reduction of efficiency and power from the engine. So what removes exhaust from the cylinders more efficient than an exhaust manifold? An exhaust header. Headers do exactly what manifolds do, except better as headers provide each cylinder head its own individual steel tube for exhaust to escape, rather than all cylinders’ exhaust flowing quickly into one plenum. All of the separate tubes direct exhaust from each cylinder head to a merge collector and away from the engine. All of the primary tubes from the cylinders with a smooth surface on the inside, ensuring exhaust moves quickly and easily to the collector, eliminating back pressure where possible. By eliminating back pressure, the cylinders are able to work more efficiently. Which will improve the performance of your hot rod!

And now we have come to the part about the exhaust flange, also known as the header flange. The header flange is the fabricated piece of steel that bolts directly to your engine on one side and attaches the steel primary tubes on the other side. Common flange thicknesses from other manufacturers range from 1/4 inch to 3/8 inch. You don’t want flanges made of thinner steel as thinner flanges will warp under heat and pressure. A warped flange will result in an exhaust leak. So avoid thin exhaust flanges. The 3/8 inch thick flanges work perfectly for street and light performance uses, but if you are going to be racing your hot rod, you will want even thicker steel flanges as we recommend ½” thick. Each flange type is made with the bolt pattern and port size and shape to match the cylinder head for you specific engine. You will want the port sizes to also fit the cylinder head exactly or slightly larger, as you do not want the header flange to restrict or block the exhaust flow in any way. Our flanges are designed from the exact port size and shape and then increased by approximately 1/16 inch larger (to account for the primary tube thickness) and then optimized to the next common available steel tube size. Also, an exhaust gasket will still be needed between the engine cylinder heads and the header flange to ensure a leaf-free fit.

Now Try Our Exhaust Flanges

You will find that we fabricate many kinds of flanges for all kinds of engines from 1925 to present. We pride ourselves in having the most complete and largest selection of header flanges and they are all made by us right here in the United States. Our exhaust header flanges are cut out of ⅜ inch P&O (pickled and oiled) steel. They are cut wExhaust Flangesith a CNC High Definition plasma cutter for accuracy of fit. The ports of the header flanges are fabricated to be used with a variety of common tubing sizes. Our flanges are designed and fit tested to make sure they work exactly as they should. We manufacture header flanges for the following makes of engines:

  • Buick (Nailhead 264-322, Nailhead 364-425, Straight 8 248-263, Straight 8 320)
  • Cadillac (Cadillac 331 (Early), Cadillac 331 (Late), Cadillac 365-429, Cadillac Big Block 425-500)
  • Chevrolet (Chevrolet 348-409, Chevrolet 4.3L V6, Chevrolet Big Block 396-454 (2.25” Round Port), Chevrolet Big Block 396-454, Chevrolet Early 6 cyl 216-261, Chevrolet Late 6 cyl 194-292, Chevrolet LS1-LS6, Chevrolet Small Block 265-400 (Rectangle Port)
  • Chrysler (Chrysler Hemi 331-392, Chrysler Poly 301-354)
  • DeSoto (Desoto Hemi 276-345)
  • Dodge (Dodge A Series 277-326, Dodge Hemi 241-325)
  • Ford (Ford 351C, 351M, 400, Ford Big Block 429-460, Ford FE 332-390, Ford Flathead 221-239, Ford Flathead V8-60, Ford Model AB, Ford Small Block 221-351W, Ford Y-Block 239-312)
  • Mopar (Mopar Big Block 350-440, Mopar Slant 6 170-225, Mopar Small Block 318-360, Mopar Small Block W-2)
  • Oldsmobile (Oldsmobile 238, Oldsmobile 303, Oldsmobile 324-374 (Split Port), Oldsmobile 324-374, Oldsmobile Big Block 350-455)
  • Pontiac (Pontiac 326-455)
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