Massive, mechanically fuel-injected, supercharged engines have been staples in drag racing. Tuners of these combinations are revered as legends since it takes a lot of skill to tame these beasts.  FuelTech has shaken things up by making it easier than ever to tune screw and Roots-supercharged engines by either integrating its ECU into mechanically injected systems, or by going with a complete standalone electronic fuel injection system instead.

How Roots And Screw Blown Engines Are Controlled

Despite the intimidating stigma surrounding mechanical injection that makes it a mystery to most, the basic concept of how it works is surprisingly simple. In regards to most supercharged drag racing applications, the engine’s crankshaft is linked to the fuel pump. As the engine spins, the fuel pump directly follows suit and feeds the engine fuel.

Although the general concept is straightforward, the trick in tuning mechanically injected screw- and Roots-supercharged combinations is perfecting that balance of fuel across an entire run to make the most power possible.

“At the output of the fuel pump, there are lines and restrictors and some go to the runners and some go to the supercharger injector hat,” explains Luis de Leon, FuelTech USA’s Chief Operations Officer. “Basically, tuners try to balance the fuel distribution between the two, with some going above the blower and some going below it.”

To make adjustments throughout the duration of a pass, tuners will incorporate pump loops to adjust the base volume and lean-outs that loop back to the fuel cell to decrease flow, both of which make the fuel pump act as if it were smaller than it really is. “Essentially, it’s like setting up a controlled leak,” de Leon notes. “When we add electronics to a mechanical system, it controls those leaks based on time, engine RPM, gear, and a whole lot of other factors.”

In mechanically fuel injected applications, because the fuel pump is directly linked to the engine, the pump gains flow as the engine gains RPM and the fuel curve isn’t actually a curve, but rather a straight-line ramp instead. However, by utilizing the aforementioned pump loops and lean-outs, you can modify the ramp into more of a curve-type shape with steps that change the angle of the ramp at certain intervals. To adjust fueling for individual cylinders, a common need in certain V8 applications where cylinders Number 6 and Number 8 often require more fuel, a tuner can simply use different jets or restrictors on the specific cylinders.

An application that uses actual fuel injectors functions pretty much like an EFI system. The injectors are tasked with feeding the engine the fuel it needs to run properly at any given RPM level. There are different ways the injectors will introduce fuel into the engine, and there are usually multiple points of entry. You’ll see engines where the injectors are mounted on a rail and introduce fuel directly into the manifold. There will also be additional injectors that pump fuel into the blower hat itself. You’ll also see some applications that use a fuel injector block, where the injectors are mounted and distribute fuel from a single point in the system.

Using FuelTech Technology To Control A Supercharged Engine

For boosted engines that use a Roots or screw blower, something as simple as losing a rocker arm on a single cylinder can be catastrophic. “The compressor still blows the same amount of air, but each cylinder receives more air because the dead cylinder isn’t receiving any more,” shares de Leon. “With mechanical injection, you’ll pop the blower because the cylinders get lean.”

However, by incorporating an ECU into a mechanically injected system, or by converting to EFI entirely with technologies like FuelTech’s FT600 system, tuners can often mitigate damage while still preserving the run itself. That level of control is one of the biggest advantages adding an ECU to a Roots- or screw-blown engine can provide.

For de Leon, who races his PJS Racing Engines screw-supercharged 4.9-inch borespace Hemi, he generally sets an engine idle of about 2,000 rpm and shifts gears close to 11,000 rpm. The FT600 EFI system actively manages a set of 16 FuelTech FT fuel injectors to precisely deliver fuel according to de Leon’s needs at each exact moment throughout the run.

“The injectors act like lean outs and are synchronized to follow the engine and pulse quicker or slower as the engine revs higher or lower,” de Leon explains. If he has to pedal the car, or if the boost goes up or down for whatever reason, the ECU reacts in real time and constantly updates the amount of fuel going to the engine. “Mechanical injection uses a fixed curve pre-defined by the tuner that only relies on engine RPM and time. If you have problems during the run, you can lose the run or the engine itself,” says de Leon.

EFI technology has progressed enough to allow it to be used in these high horsepower applications.

Conversely, thanks to EFI’s closed-loop system with boost references, O2 sensors, fuel pressure sensors, and so many other bells and whistles, the computer can compensate for a variety of changes and automatically fix things on the fly during the run. This translates to better reliability, less parts breakage, more consistent passes, and quicker elapsed times.

This also means that, if a cylinder goes out on a pass, instead of risking the entire engine or aborting the run, the ECU can protect the engine while still enabling the lap to be completed. “The other cylinders would compensate for the one you lost. You might go a little slower than if nothing had happened, but it could mean not having to fix a blown-up intake or even still winning the race,” added de Leon.

Of course, not everyone will want —– or need —– a full-blown (pun intended) EFI system. For those wanting to stick with the tried-and-true mechanical injection system, FuelTech can definitely bring a lot of advantages to the party.

FuelTech’s mechanical fuel injection controller function incorporates eight individual timer systems and RPM windows with three zones that can be activated or deactivated as lean outs. Additionally, FuelTech incorporated safety measures for engine RPM and time, adding some handy, and cost-effective levels of protection for high-dollar engines.

A FuelTech ECU can increase the accuracy of how a tuner controls the engine’s mechanical fuel injection system.

“FuelTech’s FT600 can control a mechanical injection setup with a crank trigger. The ECU knows where the engine is at in terms of RPM, and can see the trans brake button, so the unit knows when you’re starting your run,” states de Leon. Of course, the FuelTech’s logging functionality also records all of the data from each run to provide valuable feedback and insights into the engine’s expected versus actual performance. “And, if you attach flow meters or sensors to the ECU, you can also see the fuel flow, both with and without your lean-outs, across the whole race. It’s pretty much an all-in-one system for drag cars that’s really straightforward and easy to handle,” de Leon explains.

With the FTSpark ignition modules, it’s possible to run ECU-controlled coil-on-plug ignition setups with mechanical injection. Additionally, FuelTech’s ECU-managed lean-out control and power management features are all big bonuses “Tuners have the safeties from FuelTech, the ignition from FuelTech, the traction control from FuelTech, it’s just the fueling side that they aren’t using with FuelTech,” says de Leon. “But there are definitely some really badass mechanical guys out there like Todd Tutterow and Jon Salemi that have records and championships and know what they’re doing, even without EFI.”

FuelTech’s ECUs have changed how Roots- and screw-blown engines are controlled. Tuners now have the ability to control a mechanically injected engine with a supercharger with the same precision as an EFI system. Those same tunes can now use the power of EFI with mechanically injected applications, something that was considered science fiction not too long ago. Using a FuelTech ECU opens up a new realm of possibilities for racers and tuners.