Image courtesy of StangTV

You want more power.

You know that for sure.

What you don’t know is why your new headers—the headers you bought to help you get that extra power—just won’t fit your vehicle. You gave your sales rep your vehicle application, the intended purpose of your vehicle, and where you’d like to see your power gains on the power curve. They just won’t fit. And no combination of sheer will and assorted curse words is going to change that.

So what went wrong?

Working with the Summit Racing technical department, we’ve identified seven of the most-common reasons why a new set of headers won’t fit the intended vehicle (outside of being the wrong application altogether). If your newly purchased headers won’t fit, the culprit can likely be found below. If you haven’t bought your headers yet, read up on the seven pitfalls below and avoid them at all cost.

#1: You’re Out of Order

In some cases, you’ll find that there is a sequence that must be followed to complete your header installation. This may include the removal of certain items to make the headers fit.

During the buying process, it is important to take note of any footnotes that come with the product description. Take time to go over any footnotes or installation notes with your sales rep if ordering by phone. Once you have your headers in hand, pay close attention to the instructions, being careful to not skip steps.

#2: Improper Swap Mounts

Engine swaps have become increasingly common.

In some swaps, the engine location may change. This is especially commonplace in vehicles going from a small block engine to a big block and vice versa. If the correct mounts were not used during the swap, engine height and location within the engine compartment will be altered, causing fitment issues.

Since all headers are designed around factory engine mounts, you’ll need to make sure you use the proper engine mounts for the swap. This will locate the engine in its proper spot and help alleviate header fitment issues.

#3: Wrong Installation Direction

If you’re standing over your engine bay during the attempted installation, you’re doing it wrong. At least in most cases.

Most headers are designed to be installed from the bottom of the vehicle. Furthermore, your car or truck will likely need to be lifted at least 18 inches off the ground to get the proper installation angle. If you’re not fortunate enough to have access to a lift, it’s time to drag out the trusty old jack.

#4: Options in the Way

What options does your vehicle come with?

Again, this goes back to reading any footnotes with the product description. If you don’t have a manufacturer’s catalog handy, it’s probably best to pick up the phone and speak with a sales rep who does. Air conditioning, power brakes, power steering, and other options may present some extra installation challenges. In some instances, an extra bracket or option may need to be deleted.

#5: 4WD Fitment Issues

Not all truck headers are created equal.

If you’re installing your new headers on a truck, four-wheel drive versions will be bent differently to accommodate the transfer case up front.

Make sure you didn’t accidentally order or receive a set of two-wheel drive-friendly headers for your 4 x 4.

#6: Unique Head Cases

Have you installed aftermarket heads on your engine?

Some heads require a special set of headers because the cylinder head manufacturer has changed the port design, port location, and spark plug location. These changes may mean the headers simply won’t bolt up to the cylinder heads properly.

Remember what we said about reading all the footnotes? It applies here, too, as most manufacturers will make note of special cylinder head requirements.

#7: Worn Engine Mounts

Worn engine mounts and even chassis flex can cause the engine location to change slightly. Unfortunately, even a 1/8-inch difference in location can cause interference for your new headers. And that means your header flanges won’t sit flat against your cylinder heads.

To get your headers to bolt on properly, it may be time to replace your engine mounts or any other worn components causing the misalignment.

One final note: It is not uncommon for headers to have dents in the primary tubes right from the box. This is not a defect; the manufacturer often creates the dents in the tubes to solve some of the very fitment issues we’ve been talking about. If the paint or coating on the headers is not broken or cracked by the dent, the manufacturer intentionally put the dent there.

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.