Multi-port fuel injection made it’s debut on Mustangs around 30 years ago, with the four-cylinder turbo SVO. This modern fuel injection system didn’t make it to the V8 5.0 until 1986, when some old-school enthusiasts decried that it was the death of modern performance. It wouldn’t take long for many to figure out that fuel injected Mustangs were as potent, if not more so than their carbureted predecessors.

While MPFI has been around for decades now, there is still some confusion, and many misconceptions about fuel injection, specifically surrounding fuel injectors. For instance how do you know what fuel injector size your specific car needs? How do you maximize the performance of those fuel injectors? And what are some of the differences between the different types, styles, etc.

Not all injectors are equal, and choosing the right one is critical to power production, and drivabiity in any build.

To answer these questions, and many more we spent some time with David Deatsch, president of DeatschWerks. DeatschWerks (DW) spent the last 10 years carving out a niche for building high quality fuel injectors for the sport-compact performance market. In recent years they’ve expanded into the modern muscle car market, and offer an array of injector products and services to suit the needs of a variety of builds from mild or near stock street cars, to 2,000 horsepower drag strip beasts.

When Do You Need Injectors

EV14 represents the latest technology in MPFI. These injectors offer the highest reliability, fastest response, and greatest atomization. DW utilizes EV14 exclusively in their Mustang injector line-up. -David Deatsch, DeatschWerks

Personalization and performance are hallmarks of owning a Mustang or any other performance car. When it comes to the car’s fuel injectors however, replacing them under the assumption that doing so will net better performance is a common misconception. According to Deatsch, “Until the original equipment injectors can no longer provide the fuel for the power your engine makes you don’t need to replace them.”

At the OE level, powertrain engineers spend countless hours agonizing over each component, including fuel injectors to give a vehicle the most performance possible. This makes those OE parts the best option until they either encounter a failure, or are no longer providing the proper fuel supply for the current upgrades. DW offers several online calculators to help enthusiasts determine what injectors they need.

One exception to this rule would be when making an upgrade in fuel injector technology. For example taking a Fox body Mustang equipped with older Bosch EV1 style fuel injectors, and upgrading it to Bosch EV14. Deatsch says this will improve performance and reliability, “EV14 represents the latest technology in MPFI. These injectors offer the highest reliability, fastest response, and greatest atomization. DW utilizes EV14 exclusively in their Mustang injector line-up.”

DeatschWerks offers a variety of online calculators to aide in selecting the correct fuel injectors and fuel system components.

Understanding IDC

A key factor in fuel injector performance is injector duty cycle (IDC). IDC is the amount of time that a fuel injector is on or open. For example an IDC of 50-percent means that 50% of the time, the injectors are open and spraying fuel. Deatsch recommends data logging the IDC to determine if replacement is required. If the injectors are at or exceeding 80-90-percent then it’s time to upgrade to a larger injector.

Deatsch recommends slightly lower duty cycles in racing applications than in street applications. This is largely due to the fact that most racing engine fuel injectors will spend the majority of their life operating at a high duty cycle. 80-percent on racing engines is also ideal because it leaves tuners and race teams a margin to grow in, meaning if they want to increase the power before the next round or race by getting more aggressive on their setup, they may be able to do so without worrying about the ability of the fuel injectors to keep up.

The calculators on the DW site can be used not only to determine what injector should fit a particular application but also the flow rate of that injector, how changing fuel pressure affects it, and what type of fuel pump is needed to feed the combination.

In street applications IDC of 80-90-percent is the suggested cutoff for a variety of reasons. First off, excessively high duty cycles create a lot of heat in both the injector coils and injector drivers. Over a period of time, this heat can cause premature failure of both of these components. Secondly, injectors do not operate as consistently at high duty cycles. Usually somewhere between 93-97% injectors will begin to “go static” meaning they will intermittently fail to close between injection events. This will cause unpredictable, excessive fuel delivery and subsequently unstable air-fuel ratios. In short, keeping your IDC below 80-90% will improve reliability of your fuel system, maximize its performance, and give you a little headroom for overboosting or adding more power later down the road.

Deciding Factors

We highly suggest that you avoid “universal” injectors unless you have a very real reason not to.

In the mid to late 1990’s most Mustang enthusiasts typically opened up a Ford Racing catalog and picked their injectors by going one or two sizes up. While that often worked back then, we have a wider array of tools, and knowledge about fuel injection than was available 20 years ago.

In addition to IDC a number of other factors that play into selecting the proper injectors include:

Number of cylinders:

  • A four or six cylinder engine that makes 400 horsepower, will need more fuel per cylinder to create that horsepower than a V8 making the same power.

Fuel Pressure:

  • Older Mustang EFI systems often operated at 39 psi as their base pressure. The current Coyote engines utilize a 58 psi fuel system. According to Deatsch, “The higher the fuel pressure the more fuel you can squeeze out of an injector.” So a higher pressure system may utilize a slightly smaller fuel injector than a lower pressure system on an engine of the same horsepower if the fuel system is properly designed.


  • Brake specific fuel consumption is a measurement of how efficient an engine is. This in turn effects how much fuel that engine needs to operate properly. According to Deatsch naturally aspirated engines have a better (lower) BSFC than a forced induction engine. This efficiency means that a NA engine will typically require smaller fuel injectors than a forced induction engine making similar power levels.

Although they put down similar power numbers when they were new off the assembly line, the SVO engine (left) requires larger injectors than the 5.0 MPFI engine that only makes a few horsepower more.

Fuel Type

  • Racers have a wider choice of fuels than ever before. Race fuel like VP’s C16 requires less fuel volume to make power than an oxygenated fuel like their Q16, and far less volume than an Ethanol fuel, which can require 30-percent more volume than race gas.

Spacers, different O-rings, and electrical adapters can add up costs if an injector is not truly a drop in fitment.

The Right Fit

True drop-in fitment is another area where DW takes a lot of pride in what they do. Fitment is not only ensuring that the injector body is the same length from O-ring to O-ring, but that the electrical connections are the same, or that the injectors will fit into the intake manifold and into the fuel rail. It also includes ensuring the injector spray pattern is matched to a specific application, and that the injector is compatible at all levels with the engine and electronics being used.

“We highly suggest that you avoid “universal” injectors unless you have a very real reason not to. Universal injector will often require additional and sometimes expensive fitment “accessories” electrical connectors alone can cost $10-$15 each. Fuel rails, fuel rail spacers, o-rings, sometimes even a new manifold is required to fit a universal injector.”


Tuning is the final piece of the puzzle in the critical process of getting the right fuel injectors. In the past several years tuning data has become more readily available from injector companies. Calibration summaries and injector data are available for every Mustang injector that DW sells, and they develop this data in-house.

New products undergo extensive flow testing to gather this data and formulate a proper injector characterization. The data is then formatted specifically for each application and validated in-car on a dyno. All of this is done before being sold to customers. “Keeping it simple for the user is key. Customers and tuners can go to the resources page of the DW website, look up their particular set of injectors, and literally cut and paste the tuning data for the fuel injector tables directly into their tuning software,” says Deatsch.

This single piece of data, provided with every set of Mustang injectors from DeatschWerks, can potentially save tuners hours in custom tuning work, and owners hundreds of dollars.

With Mustangs the data needed to tune includes:

  • High-Slope: This number defines the linear range of the fuel injector which typically consists of pulsewidths greater than 2-3 milliseconds. It is needed for proper tuning under high throttle conditions.
  • Low-Slope: This number defines the non-linear range of the injector which typically consists of pulsewidths less than 2-3 milliseconds. It is needed for proper tuning of idle and light throttle conditions. This is the part throttle, lower power driving situations.
  • Break Point: This number defines the transition point from non-linear (low pw) to linear (high pw).
  • Battery offset: This table compensates for variations in battery voltage which can effect the opening time of the fuel injector.
  • Having all of this data available means that even on high powered applications drivability is vastly improved because the injector tables are fine tuned from this information. This also saves even the most experienced tuners a lot of time, since they will not have to find a starting point based on their experience and then conduct drivability, and other tests to refine the injector portion of a custom tune.

A DW technician prepares a set of injectors for flow balancing.

Fully Balanced

According to Deatsch, flow balancing plays a critical role in creating a truly matched set of injectors.

DW has developed a proprietary system for flow-balancing known as Multi-Point Dynamic Flow Balancing (MPDFB). In the past, injectors were typically tested using static balancing. This process ran the injectors wide-open “static” for a set amount of time. Each injector sprayed liquid into a graduated cylinder during that cycle, and the numbers from each were then compared. Injectors were then typically grouped together in sets that had similar “static” flow rates.

The trouble is that fuel injectors are not static fuel metering devices. “Fuel injectors are very dynamic components, constantly opening and closing multiple times per second,” syas Deatsch. This is why he says that DW developed their (MPDFB) system. “This type of flow balancing quantifies the fuel delivery of each injector across the full range of pulsewidths injectors operate in the car. This includes a low, or start condition pulse width, idle pulse width, mild acceleration pulse width, and high, or full throttle level pulse widths.”

Left: Injector balancing is performed using graduated cylinders. Injectors are then run over a variety of duty cycles to check their flow rates. This set is not balanced due to the large discrepancy between their flow numbers. Right: This set of injectors is considered balanced because their flow is very closely matched, meaning they will deliver consistent fuel delivery across all cylinders.

The MPDFB process could be compared to blueprinting an engine or looking at the area under the curve on a dyno graph. All of the data is recorded and compared, and each injector is scribed with an identifying number so it can easily be referenced. By doing this injectors can be precisely matched as a set, ensuring consistent performance at full throttle, and stock-like starts, idle quality, and drivability in all other driving situations.

Quality And Service

EV1, EV14, GDI, and more. DeatschWerks can provide Mustang owners with the right injector for their engine.

The last area to look at when selecting a set of injectors for any performance application is the quality of the product and the customer service. That guy selling “refurbished” injectors on eBay is likely not going to give the time of day if or when there’s a problem with installation or tuning. Having a company that is easily accessible and eager to help their customers creates a kind of partnership through that level of service, and is paramount to getting any project car set up properly.

According to Deatsch all of the factors we’ve discussed in this article are critical in creating a good product, but customer service is also a key at DW. Getting tech support to choose injectors before the sale, and then helping with tuning, or trouble shooting after the fact is something DeatschWerks prides themselves in, along with their extensive R&D process and injector services.