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How to Properly Dimple Headers

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Headers help your engine breathe, but so many times there are interference issues that make fitting a set of headers in your car difficult. Most aftermarket designs for the GM A-body are fairly well-tested, but different components don’t always gel, so you take matters into your own hands. Contrary to popular belief, dimpling headers make no discernable difference in power. In fact, in some tests dimpling even increased power by a few ponies. One dyno test in particular showed that even severe bashing of all 8 primary tubes in multiple places had zero effect in performance. So now that you know it is OK and won’t hurt your engine’s performance, what is the best way to do it?

There are several methods to dimpling a header tube. Most folks just go bananas with a hammer, but this leaves an ugly mess that while effective, is not very scientific. Others suggest filling the tube with sand to add some resistance; supposedly this makes a more uniform dent. The other method, the one we will demonstrate here, uses heat to soften the steel, and a hammer to make the magic happen.

The first step is finding the spot where the problem is located. On this Buick GS, we have a set of custom headers that were built to test the clearance of an LT1 in the A-body. These are LS-swap headers with LT1 flanges. Unfortunately, the angle at the flange is not quite right, and the primary tubes hit the starter flange and the knock sensor on the passenger side. Eventually we will get a proper set of headers, but for now, a dimpling we shall go.

With the headers marked, they were removed and loaded into a sturdy bench-mounted vise. Then we applied some heat with an oxy-acetylene torch in just the area we needed to dimple. This is important, because we want to make just enough of a dent to clear the area, and we don’t want to distort the surrounding pipe. Be careful not to melt through the tubing.

Once the pipe is glowing red, we hit it with the hammer in the center, working outward. For smaller dimples, the round ball side is best, but for larger areas, we used the flat side of the hammer. Then we let the headers cool naturally. Placing them in front of a fan will cool them off in just a few minutes.

We checked the fitment and any additional dimpling performed until the headers fit. While it is not something you want to do, it is often necessary in order to get the headers to clear the chassis or other engine components. Just be careful not to close the tube or cut a hole in it, but if you do put a hole it, you can always weld it up.

Sometimes parts don’t fit like they should, especially headers. A one degree variance at the top of the head can be a couple of inches at the bottom of the header. These headers are modified, the tube arrangement is for an LS-swap with LT1 flanges. That didn’t quite work as planned as the passenger side hits the bellhousing.

Sometimes parts don’t fit like they should, especially headers. A one degree variance at the top of the head can be a couple of inches at the bottom of the header. These headers are modified, the tube arrangement is for an LS-swap with LT1 flanges. That didn’t quite work as planned as the passenger side hits the bellhousing.

 

Using a torch, the pipe was heated up to cherry red. Be careful not to melt the metal.

Using a torch, the pipe was heated up to cherry red. Be careful not to melt the metal.

 

Then the pipe was hit with a hammer to dimple it. This is a trial and error process, it usually takes a few tries to get it right.

Then the pipe was hit with a hammer to dimple it. This is a trial and error process, it usually takes a few tries to get it right.

 

This should get the job done on this pipe, next please.

This should get the job done on this pipe, next please.

 

Cherry red is the ticket to a smooth dimple. This allows for a more precise dent as opposed to crushing the surrounding metal too.

Cherry red is the ticket to a smooth dimple. This allows for a more precise dent as opposed to crushing the surrounding metal too.

 

The ball-side of the hammer is good for working the corners of the dimple. You want the dimple to be as smooth of a transition as possible.

The ball-side of the hammer is good for working the corners of the dimple. You want the dimple to be as smooth of a transition as possible.

About Jefferson Bryant (221 Articles)
A life-long gearhead, Street Tech Magazine founder and editor Jefferson Bryant spends more time in the shop than anywhere else. His career began in the car audio industry as a shop manager, eventually working his way into a position at Rockford Fosgate as a product designer. In 2003, he began writing tech articles for magazines, and has been working as an automotive journalist ever since. His work has been featured in Car Craft, Hot Rod, Rod & Custom, Truckin’, Mopar Muscle, and many more. Jefferson has also written 5 books and produced countless videos. Jefferson operates Red Dirt Rodz, his personal garage studio, where all of his magazine articles and tech videos are produced. You can follow Jefferson on Facebook (Jefferson Bryant), Twitter (71Buickfreak), and YouTube (RedDirtRodz).

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