Ask An Expert: Dual Injection Tuning With ZFG Racing And FIC

Modern fuel injection has come a long way in making our engines run cooler and more efficiently. With the introduction of dual injection, both port and direct injection, the tuning aspect has had to evolve to satisfy the demands of owners wanting more performance from their modern platform. This stirred a need for tuners to develop new techniques, acquire more data, and add a few steps to their process in order to make sure both injection systems function together and optimize the performance of the vehicle without affecting driveability.

We wanted to get a good understanding of what to look for in an injector and how the two fuel injection systems work together from a tuner’s perspective, so we sat down with Adam Staszak from ZFG Racing to ask some questions.

James Elkins (JE): What do you look for in an injector?

Adam Staszak (AS): I look for the data to be drop-in and match the format of the stock injector data. Where the data doesn’t match scale-wise, I usually reach out and ask if the injector company can reformat it. Fuel Injector Clinic was the only one that jumped in and reformatted the data for higher pressure ranges, which made a big difference in the tune stability.

JE: How much does data-match help tuning?

AS: It’s key. You cannot tune based on bad injector data. This is especially true for the stuff I do, which is dual injection, both port injection (PI) and direct injection (DI). Normally, with PI only, if you have injector data that is slightly off you just end up tuning around that. With dual injection that is kind of hard to do, because only part of the required fuel load is coming from the port injectors, and it’s a different percentage based on load and RPM. So, having that data right the first go’round is super important..


JE: Is it true that DI does most of the heavy lifting? Does this change what you need in a supplemental injector?

AS: That’s not actually true. Once we swap over to bigger injectors (which is almost always because we want to run E85) the workload is closer to 50-percent, once you hit full boost. In a lot of the race applications, you’ll actually see the port injectors providing 60- to 70-percent of the fuel flow required. This is, of course, application-specific. In this case we are talking about the Gen-2 3.5-liter EcoBoost in the F-150, which actually has a very small DI system relative to the previous generation of 3.5-liter EcoBoost.

JE: Does idle quality become moot at this point?

AS: Idle quality is still important, but in some cases, we can just go to 100-percent DI at idle to get around large injector idle issues.

Here is a stock 3.5-liter F-150 DI/PI blend table where 100-percent is 100-percent DI and 0-percent is 100-percent PI.

JE: Is the supplemental PI still running at 43.8 psi, or is it higher? Would there be any benefit to running higher pressure?

AS: In a factory DI/PI system we are always running high pressures. Ford does not use boost referenced fuel pressure – it is controlled by the ECU. Typically, on a DI/PI system the low-side pressure is going to be dictated by the minimum high-pressure fuel pump (HPFP) inlet pressure. From the factory this ranges between 55 and 73 psi, with 73 psi being the requirement on pretty much anything over 3,500 rpm.

On a DI/PI system the low-side pressure is going to be dictated by the minimum high-pressure fuel pump inlet. This can been when comparing fuel temperature and engine speed.

JE: How is the supplemental injector sizing calculated?

AS: This is hard DI system sizing is typically limited by the size of the high-pressure fuel pump. I have a program that I wrote that can give me the max fuel flow rate based on the pump size and volumetric efficiency (VE) table for the high-pressure fuel pump. From that number, I can basically work backwards and say the DI side can support 400 wheel horsepower on E85 – how much port fuel system do I need to meet my goals?

JE: You mentioned Fuel Injector Clinic at the beginning — is there something they bring to the table that helps your tuning process?

AS: I prefer Fuel Injector Clinic because they are willing to do what it takes to provide the right product and data. As I mentioned, it was very key to have the injector data rescaled for the EcoBoost application. That made all the difference in tuning, and they did that for me almost the same day, whereas other injector companies didn’t listen to my request, dismissing it as not needed and then taking weeks to provide the data after realizing it was needed.

In Depth With Fuel Injector Clinic

We wanted to gain some more knowledge about the processes that Fuel Injector Clinic takes to provide such a highly recommended and high quality product. So we decided to go straight to the source. We reached out to Fuel Injector Clinic’s Head of Sales and Marketing, Randy Earle, to let the answers flow about the products and processes at the Fuel Injector Clinic headquarters.
JE: What has Fuel Injector Clinic done to ensure its injectors perform at a high level of performance?

Randy Earle (RE): We have invested a great deal into developing our proprietary injector test bench that allows us to characterize injectors at the highest level possible. In fact, our technology is so advanced, we have been asked to match injectors for NASCAR teams, where accurate fueling can mean the difference between winning and losing a race.

JE: Does Fuel Injector Clinic have a threshold for data matching variance?

RE: Our injectors are matched for flow at less than 1-percent, and less than 2-percent for dead times.


Our injectors are matched for flow at less than one-percent and less than two-percent for dead times. Randy Earle, Fuel Injector Clinic head of sales and marketing

JE: What is the process each injector faces before shipping out?

RE: Each injector is flowed and characterized on our flow bench. Once this is completed, that injector is serialized and entered into a large database of injectors flowing the exact same size. When you call and order a set of eight injectors for your vehicle, we pick eight injectors out of our database that are matched at the highest level for both flow and dead times.

JE: Does Fuel Injector Clinic offer a warranty on its products?

RE: All of our injectors come straight from Bosch, and every injector we sell is compatible with E85 and comes with our lifetime warranty.


Precise fueling is often overlooked during a vehicle’s build phase, but is easily recognized as problems arise during tuning. Fuel Injector Clinic provides a high quality answer that solves tuning woes. So, if you’re looking for injectors that come accompanied with great ECU tuning data and are data-matched  to provide low variance, then Fuel Injector Clinic might be the best answer for your combination.

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About the author

James Elkins

Born into a household of motorsport lovers, James learned that wrenching takes priority over broken skin and damaged nerves. Passions include fixing previous owners’ mistakes, writing, and driving.
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