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Upgrading Fox Body Cylinder Heads

Written By: Connor MC

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It's no secret that the old-school 5.0 Foxbody motors are underpowered in today's age. It is also well-known how easy it is to wake up your 5.0 with a few engine modifications. Stock Foxbody cylinder heads have very poor airflow but, luckily, the Mustang aftermarket has a ton of upgrades available.

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To squeeze some more ponies out of your Fox Body Mustang, upgrading the cylinder heads can lead to some substantial results. This guide contains a Fox Body Cylinder Head Flow Chart and information on available upgrades, ranging from the stock E7 heads to fully prepped, CNC machined aluminum beauties.

American Muscle

A Matter of Airflow

The 5.0 equipped Mustangs, in their day (1987-1993), were nothing to shake a stick at. However, come the 21st century, the meagre 225HP output by their mighty 50.L V8's is just way to low compared to modern standards. Luckily, despite the age of these cars, ongoing research and experimentation by aftermarket companies have yielded some impressive new parts to really waken up that low-on-power 5.0. It is common knowledge that a major restriction point, from a power perspective, is found within the factory-cast E7TE heads that originally came equipped with the Foxbodies. They just don't flow enough air into the engine. 

Like previously mentioned, the E7TE heads (stock heads on 1987-1993 5.0L Mustangs) don't flow enough air. They also weigh quite a bit, as they are cast from iron. This guide presents the best options to upgrade your Fox Body Mustang's cylinder heads.

Porting Fox Body Cylinder Heads

Porting heads involve using a rotary tool (dremel) and a burr to restructure the passageways to optimize air flow through the cylinder head. Remove unnecessary casting material, smoothing out imperfections, polishing the chambers are all part of the process. Porting can yield some results. However, done on these E7 heads, even an A job may only yield a 30HP gain. 30HP is nothing to sniff at, except that porting is very expensive. Unless you do it yourself, you will have to pay a professional (the general consensus is they usually charge an arm and a leg) to do it for you. At the end of the day, it isn't really logical to spend $500 for someone to port these iron heads for a measly 30HP. Of course, you can do it yourself. Many enthusiasts have. With some dedication and careful work, you can port it yourself. Alas, it is also just as easy to hamper performance as it is enhance it if you are a beginner. Iron is also somewhat difficult to work with.

Replacing Fox Body Cylinder Heads

At the end of the day, E7 heads just aren't really worth the money to improve. Aftermarket options have come a long way. They offer incredible power improvements over stock AND room to grow. In comparison, E7s are nearly maxed out in stock form. Read below to get an overview of what the aftermarket has to offer.

Aftermarket Fox Body Cylinder Head Options

The aftermarket offers astonishing improvements over stock heads, for both forced induction and naturally aspirated applications. Some well-known names are Edelbrock, Trickflow and of course Ford's own performance branch, Ford Racing. Benefits from these aftermarket heads are simple - better design, lighter weight, more power! All of these heads are of superior design and quality. They also are all made from aluminum which gives a significant weight savings over the stock cast-iron heads. Furthermore, they are all a direct bolt-on! No fiddling or special modifications necessary to have them fit on your 5.0L roller block.


Foxbody Mustang Edelbrock cylinder heads
Edelbrock E-Street Cylinder Heads

Edelbrock has several models for those considering upgrading their cylinder heads on their 5.0L V8. The E-Streets and Performer heads are the most popular choice from their range of products, with the former being their lowest entry option. Both offer an aluminum design, 170cc intake ports and valve sizes. The E-streets are intended for those with the budget in mind and subsequently do not offer the same amount of performance as the Performers do. As part of a cost saving procedure, the E-Streets use weaker valve springs and may need new ones as the supplied ones are only for very mild cams (stock HO cam is too much). Edelbrock's Performer heads are a little more robust. Both Edelbrock models are considered entry-level aftermarket heads for a mild street build, with a power range from idle to 5500 rpm. With the right combination, these heads can support 300-350HP (flywheel) without issue.

Ford Racing

Ford Racing GT40x cylinder heads
GT40x Aluminum Heads

Ford Racing has a longstanding history with aftermarket parts. Specifically, their latest generation GT40 aluminum cylinder heads. Based off the original and incredibly popular GT40 iron head (from the 90s), Ford has continued to improve this horsepower adding design over the years. Today, their efforts come to fruition in the GT40X Turbo Swirl 178cc cylinder heads. Claiming a hefty 240 cfm of flow at 0.550 lift and a commanding 65HP gain, these are some solid heads. These GT40Xs are comparable to the Edelbrock Performers - similar pricing and similar performance. They are a great step up from the stock E7s. Again, very good for a mild street/strip build supporting between 300-350HP, depending on what other parts are on the car.


Trick Flow Foxbody cylinder heads
Twisted Wedge 64cc Heads

Trickflow, as its name implies, does use tricks to increase airflow on its 5.0L compatible Twisted Wedge 170cc head. By far this is the most popular choice among Mustang enthusiasts. However, it is also the most expensive. But as some would say, you have to pay to play. Trickflow Twisted Wedge heads use dark magic to make power. Trickflow has rotated and moved the valves from their traditional position to a position atop the cylinder bore. What does this mean to you? This voodoo supposedly optimizes and increases airflow and thus power. Like the others, these heads are great for a mild street or track build. 300-350HP is not hard to come by with these heads. However, they do have one extra trick up their sleeve. In my opinion, the Twisted Wedge heads have the greatest amount of potential, i.e: plenty of room to grow if you need more power.

Fox Body Cylinder Head Flow Chart Comparison

All numbers are issued by manufacturer. Measured in CFM.
All numbers are issued by manufacturer. Measured in CFM.

Here we have a comparison between some of the leading performance cylinder heads available for Foxbody Mustangs and the stock, Ford E7TE heads. As you can see, Edelbrock, Ford Racing and Trickflow all produce competitively performing heads, each having their own advantages/disadvantages. Choosing the right cylinder heads for your Fox Body build is essential and will help you determine the overall direction for the rest of the car.

Choosing Aftermarket over Stock Fox Body Cylinder Heads

As you can see from the flow numbers, any of these aftermarket aluminum cylinder heads will really wake up that 5.0L slumbering beneath the hood. Furthermore, they are available in different stages and packages. For example, you can by these aftermarket heads as cast. Or, if you prefer some more power and at an added cost, you can opt to purchase a CNC machined version which will have better airflow over the as cast version. Each head can come equipped with different spring packages, smog equipment provisions etc. There really is nothing that Edelbrock, Ford Racing or Trickflow has left out. Extra power certainly can be squeezed out of the stock E7s, but with the design and technology implemented within the modern aftermarket heads they really are the best choice.