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What is an HCI Swap on a Ford Mustang?

Written By: Connor MC

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Heads, cams and a free flowing intake are great for power gains, get all you need right here. If you want even more ponies under the hood however, you might want to check out some power adders like a turbo, supercharger or a N20 system.

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If you have ever browsed the performance section of an online Mustang enthusiast forum, chances are you have come across some member or another recommending to someone else to do an HCI swap. What the heck does this mean? It’s a universal acronym amongst gearheads that refers to Heads, Cam, Intake (HCI), 3 essential top end parts to any engine.

American Muscle

HCI Swap – Cylinder Heads, Camshaft, Intake

To extrapolate a little further, completing an HCI swap means to replace the stock cylinder heads, the stock camshaft and the stock intake with aftermarket pieces that will allow the engine to perform better. In the circumstance of the cylinder heads and intake, aftermarket versions are usually able to flow more air into the engine at any given RPM, thereby allowing the fuel system to inject more fuel and make more power. 

An aftermarket camshaft, on the other hand, will have revised characteristics that change duration (amount of time valve is open), overall lift, valve overlap etc, all in the name of making more power. The power band of the engine will usually change as well.  

Boss 302 Intake Plenum

Why Would Someone Recommend This?

You will come across this ‘HCI’ acronym most often in threads that are asking about how to increase horsepower on a Ford Mustang. Simply put, these 3 pieces play a major role in the performance of the engine. The key to having a powerful Mustang is being able to get the maximum amount of oxygen into the motor, per cycle. There are a few ways to do this.

  • Increase the displacement: Increasing the displacement of the motor essentially is enlarging the cylinders (not their width, but usually their length). Larger cylinders mean they have more volume for air to flow into. More air = more fuel = more power.
  • Forced induction: Using a supercharger or turbo charger is another way to see some great power gains. Essentially, all a super or turbo charger does is cram more air into the same space (greater density), giving the fuel more oxygen to react with.
  • HCI swap: Swapping the top end with better flowing parts allows more air to flow into the combustion chambers at any RPM, making more power. If it helps, think of an HCI swap as allowing the engine to breathe more, and better. 

All 3 of those methods use the same principle – get more air (and oxygen) into the engine. They just go about it in different manners. Furthermore, you don’t have to limit yourself to just one method. If you combine all 3 on the same motor, expect your ‘Stang to reverse the rotation of the earth! Each method is accumulative. 

Set of cams for a DOHC setup

What Kind of Power can I Expect?

There isn’t a definitive number to answer this question, unfortunately (as all engines are unique). However, swapping out the stock cylinder heads, the stock intake and the stock camshaft(s) with an aftermarket version can lead to some real big horsepower gains, especially on the older pushrod V8’s (Foxbody guys).

In fact, for the Foxbody owners, replacing the stock top end with the latest pieces can net an easy 100 HP!  The later modular motors will not gain as much as that, but there are gains still to be had, in the neighborhood of ~50HP.

The name of the game is about getting oxygen into the combustion chamber, and a well matched HCI combination is going to maximize this.

Ford Racing Mustang Cylinder Head

What is the Cost?

This question too is quite subjective to not only the year of the car, but to its condition as well. The parts alone usually run for $2000-$4000 total, but then there could be labor on top of that, or additional problems that crop up during the process. For example, say you have a ’91 GT that is leaking oil real bad, you’d want to fix that when doing the HCI swap, so the overall cost would be a little more. 

More often than not, you can buy the parts packaged as a matching kit (a kit the manufacturer has deemed to work well), saving some cash by purchasing as a bundle as opposed to each part individually.

JLT Mustang Cold Air Intake

OK, If an HCI Swap is so Great, Why Doesn’t Ford Just Upgrade it from the Start?

Aha, this is the million dollar question, and a very good one at that! Luckily for me, it is also an extremely easy one to answer. If all it takes to make some more ponies is to swap the cylinder heads, camshaft and intake on your Mustang, well, it sounds foolish that Ford wouldn’t do it from the start. The reason Ford does not do it is cost. 

Simple as that. Making and machining a cylinder head is no easy task. It takes serious engineering, testing, and then even more serious machinery and tooling to actually manufacture the parts. Every piece on any Ford product has to meet certain criteria, and part of those criteria is cost effectiveness, part versatility and ease of production. Ford strives to re-use as many of their parts as possible across all of their vehicles so they can reduce engineering costs, tooling costs and production costs. Imagine if Ford completely redesigned their cylinder head every year, it would cost them a fortune in new machinery alone. Instead, they make revisions. Small changes are made here and there to increase one aspect or another, but nothing too drastic that it requires completely new robots, or would make it incompatible for another platform.

Pair of Mustang cams
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