Hide EFI in Your Next Project
Has Holley Nailed the Perfect Mix of Nostalgia Style and Modern Performance?
With the advent of bolt-on EFI, we knew this day was coming; they didn’t just come for the carburetor to replace it as a fueling system, they came and stole every bit of the carburetor’s retro-cool looks, too. As much as carbs were chosen for their practical strengths, to some folks, their look called back to the right period for many projects. Holley understood this and machined up a throttle-body that took all the technology it has developed with the Terminator and Dominator EFI systems and packed them into a double-pumper doppelgänger. This is where Dale Snoke’s 1964 Mercury Comet— a traditional A/FX Gasser that runs nostalgia races all over Socal—comes into play. Car Craft readers might recognize Dale’s Comet from the 2016 carburetor test sizing up which cfm of Holley double-pumper was ideal—ironic that we’re here to erase all that hard work with Holley’s self-learning EFI.
As a quick refresher, The Rocket is powered by a 425ci Windsor (4.060 bore with a 4.100-inch stroke) topped by a set of 195cc AFR Renegade heads that are stuffed with 2.05/1.60-inch valves, which all tap to the rhythm of an Isky roller cam (260/260 with 0.620-inch lift and a 110-degree LSA). The wild, through-the-fender headers are homebuilt by Dale, an electrician and welder by trade, and he’s fabricated two separate exhaust systems, one muffled and one baffled, depending on the noise restrictions for the day’s activities. This is notable in our EFI test, as open headers with an O2 sensor in the collector need extra exhaust length to ensure an accurate fuel-ratio readout; without some kind of extension, ambient air can get pulled into the collector between pulses, skewing O2 sensor readings—this is avoided in Dale’s configuration. Out back, a C4 built by Nick Magana, handles the gear shuffling and a Ford 9-inch with 4.30 gears lays down the power with a set of plain, old leaf springs. This is a bare-bones, street-ready combo that churns miles to a cruise night across Los Angeles as well as it churns out 6-second eighth-mile passes.
We’ve observed many EFI baptisms over the years, but this one is special: with Dale’s Comet staying true to its altered-wheelbase roots, could we build an EFI system that blended right into the vintage underhood landscape of gold Moroso valve covers, wildhair headers, and prominent MSD dizzy? And better yet, would EFI’s closed-loop selftuning for conditions make the car quicker, if not more consistent? With a weekend’s worth of effort, we found out.
Holley’s new Terminator Stealth EFI is a variation of its other four-barrel, throttlebody–injected EFI systems. Thanks to Moore’s Law—the one that states technology shrinks and becomes more capable on an exponential rate—Holley has squeezed four injectors, a throttle position sensor, idle air control valve, MAP sensor, and intake air-temp sensor under the façade of a classic double-pumper. This means the only external sensors that you have to think about are for coolant temp, air/fuel (A/F) ratio, and rpm. Holley was mindful to sheathe its wiring in a similar braiding as its fuel lines, so the harness quickly blends into the environment if routed appropriately. For control,
Terminator Stealth uses a variation of the familiar HP-series ECU with four input/output channels for additional controls, such as fans, a shift light, or nearly anything else you can dream up to be triggered or read by the unit. This also means complete laptop tuning when needed, though for this test we wanted to put all the weight on the ECU’s shoulders in figuring out this nostalgia combo. Holley also included an external high-pressure fuel pump for our kit (PN 526-5), which we’ll test in this combo.
To adapt the Terminator Stealth Kit to the Comet, we also ordered a pair of Holley’s -8 AN billet 175-gph fuel filters (10 and 100 micron; PN 162-554 and 162-564, respectively) as a pre- and post-filter, though we stuck with the included pump for this test. The billet filters allowed for a tidy adaptation to the existing -8 plumbing, and we’ll test other pumps in this combo down the road with full AN connections. We also decided to go with Earl’s braided fuel line given the track usage (and tech-inspector eyeballs) here, though the included Vapor Guard fuel hose is more than up to the task in a streetdriven project and technically meets NHRA approval. We paired a Holley 15- to 65-psi (PN 12-846) fuel pressure regulator with the system to maintain the recommended 43 psi of fuel pressure.
It’s at this point that we’ll delineate some terms, separating self-learning from the closed-loop, self-tuning aspects of Holley’s EFI. Holley’s lauded self-learning is the process in which the ECU adjusts its own base calibration (an X/Y table that compares load versus rpm, resulting in a target A/F ratio, depending on that condition) around the engine combo you’ve told it to run. This is because every engine will react differently to throttle, timing, and fueling adjustments in normal use, and the self-learning adjusts the base calibration so there’s less and less compensation to hit the target A/F ratio. What this step replaces is that initial calibration that was a major barrier of entry to many stand-alone EFI systems.
Building and dialing in a base calibration was either a relatively expensive (though very valuable) stop at a tuning shop or required a wealth of upfront knowledge to DIY. With Holley’s self-learning, that initial calibration is entirely handled by the ECU while driving—and it must be trained. This is done by driving the car across the rpm range at different throttle positions, working it through that Load vs. RPM table in as many areas as possible. We recommend starting with drives around the block and moving on to highway trips. This will build out the low- to medium-load ranges of the base calibration, which help the ECU predict what to do with full-throttle loads. We had
to fatten up the cruising target A/F ratio, but within about 50 road miles, the selflearning had gotten the hang of Dale’s stroker.
Self-tuning is what we’ll refer to as the closed-loop condition of EFI, where the car is using the base map and calculating the amount of fuel necessary based on the atmospheric conditions read by its various engine sensors—this is the real advantage of EFI. In general, the magic of carb tuning isn’t in making a big dyno number, it’s in adjusting the carb to ambient conditions to optimize the fuel curve. This meant a trial-and-error process of taking a pass and making a messy jet change between rounds—goldilocks with timeslips. This is the magic of EFI; since the ECU does this on the fly during the run—ensuring that you not only maximize power output but also keep the engine in a safer envelope of tuning—the car won’t suffer as much from bad air, and we theorized that most of the performance advantage on track would come from this second-by-second consistency.
[ If it weren’t for the giant EFI lettering, you’d be right to pick up this box expecting a four-barrel carb. The Terminator Stealth EFI comes in a polished, black, and gold finish to match your common carburetor looks.
[ We cut down the vibration insulation of our pump to expose the body. Given the heat radiated off California highways, we had heard this can prevent fuel boiling.
[ Holley’s 15- to 65-psi billet fuel pressure regulator was the keystone of this build, giving us a port for our return line while also adjusting for EFI’s higher pressure over a carbureted fuel system.
[ A mounting bracket was cut out of3⁄16- inch steel, which housed the inlet filter (10 micron) and pump. The downstream filter (100 micron) was mounted in place of the former Holley Black Pump.
[ A short piece of fuel hose was used as our return to prevent the fuel from “waterfalling” into the fuel cell, creating cavitation-inducing bumpers.