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Tech Review—Engine Management for Under $1,000, AEM Series 3 Engine Management System and CD-7 Digital Display

Justin Spencer’s 2000 Roush Mustang was the perfect candidate for the Infinity Series 3 with its fortified 4.6L Two-valve Mod Motor. It features Trick Flow cylinder heads, Edelbrock intake manifold, and a Vortech V-2 Ti supercharger. On the chassis dyno it spits out 608 rwhp through the TH400 automatic and it’s run a best of 9.32 at 149 mph.
By Miles Cook

Photos by AEM Performance Electronics and FSC Archives

It is a horsepower war that has simply crushed the golden era of the ‘60s with OEs getting in on the fun with cars like the 840hp Dodge Demon and all three manufacturers offering supercharged 8-second drag racing packages. For older muscle cars, converting to EFI has never been easier with inexpensive plug/play kits up to stand-alone units that can control virtually every system in the vehicle. The technology boom is quite apparent in our beloved high-performance world from the aftermarket to the big three automakers.

The Mustang and late-model GM markets have proven that even a mostly factory car can turn 9-second runs and there are a lot of great options for re-calibrating the factory ECU. However, as racing intensifies so does the need to have more control on the engine management side of the equation. Our example is longtime West Coast racer and multi-time NMCA WEST champion Justin Spencer. His 2000 Roush Mustang runs deep into the 9s with a Vortech-supercharged 4.6L Two-valve Modular combination. The factory ECU benefited from a custom tune delivered by a DiabloSport hand-held programmer, however the tough competition in Open Comp and Index racing dictated he needed more control.

“It was inconsistent in the high rpm, usually after 7,400. It was hit or miss if it would accelerate past that rpm,” noted Spencer. He mentioned the problem was most likely the computer couldn’t read the cam and crank signals in the upper rpm ranges. He was definitely a candidate for a stand-alone EFI system, which sent him hunting through the marketplace.

Navigating the aftermarket ECU segment could be tricky, there is a balance of the system’s capabilities and, of course, pricing. Through racing he was familiar with AEM Performance Electronics, so he started looking at the systems they offer. There is a significant amount of attention placed on the AEM Infinity Series 7 ECU, especially with its successes in the Coyote market. For Spencer, his combination didn’t require all of the options since his engine is fairly basic, most notable differences being the locked camshafts of the 4.6L SOHC style engine and the cable-controlled throttle body instead of the drive-by-wire setup.

A step back from the high-profile Series 7 is the reasonably priced and highly capable Infinity Series 3. It is designed for most popular early- and late-model, throttle-body and port-injected Ford, GM, and Mopar V-8s. The Series 3 ECUs are simplified engine controllers designed to run a basic race, marine, or crate engine without the need for, or cost of, additional features like variable cam control, drive-by-wire throttle control or internal wideband air/fuel sensor controllers. The Series 3 includes the Infinity 308 (PN 30-7113) and Infinity 358 (PN 30-7114). Both Infinity Series 3 systems are offered for an amazing low price of $999.

Infinity 308 Programmable EFI

The Infinity 308 features two different injector types and two different coil outputs that support three different types of fuel and ignition configurations.

For throttle-body-injected (TBI) and GM multi-port fuel injected V-8s the Infinity 308 includes a single direct-drive ignition coil output to work with a distributor and a single coil, and two peak-and-hold injector drivers that can drive up to four high-impedance injectors each. Other port injected and single-coil-distributed V-8 engines like pushrod Ford and Mopar engines can be controlled using the Infinity 308’s eight high-impedance injector drivers and single direct-drive coil output.

For the GM LS, the Infinity 308 has eight high-impedance injector drivers and eight “smart” coil outputs to drive LS coil-near-plug ignition systems.

Infinity 308 MEFI Upgrade
The Infinity 308 is a great upgrade for users looking to replace their older MEFI-4 system. This system also provides users with an upgrade path to sequential port-injection and “smart” coil-near-plug ignitions. A plug-and-play adapter harness to install an Infinity 308 on engines using MEFI controllers will also be available.

Infinity 358 Programmable EFI

The Infinity 358 is designed to control two- and four- valve Ford Modular SOHC and DOHC engines, late-model Dodge Hemi engines and other late-model, individual direct-drive “dumb” coil V-8 engines with port injection using eight high-impedance injectors.

Designed for the price-conscious racer, the Infinity Series 3 incorporates all of the features necessary to run a high-performance engine including airflow-based VE tuning for fuel-injection control, ignition control, flex fuel, knock control, boost control, nitrous control, launch control, traction control and engine protection. The Series 3 is able to communicate with third-party dashes and loggers and is AEMnet CANbus enabled to easily communicate with other AEMnet equipped devices including the AEM CD-7 and CD-7L. All maps can be password protected. Its latest generation 200MHz processor can process 400 MIPS (millions of instructions per second).

Air/fuel ratio (AFR) feedback is supported by adding external wideband controllers through 0-5-volt analog inputs or via AEMnet CANbus using AEM’s X-Series Wideband UEGO AFR controllers. An engine history feature is included that records basic engine operational conditions including run time, peak rpm (overrev), oil pressure/temp overheat (requires sensors, sold separately) and lean condition (boost/vacuum vs. AFR). All of the parameters of the engine history feature are user programmable.

Both systems feature a small, thin footprint (7.35 x 6.55 x 1.8), lightweight case (29.9 ounces/848 grams) with 73-pin connectors. The Infinity Series 3 enclosure is fully sealed and the connectors are IP67 rated (dustproof, waterproof to 1 meter) making the Infinity suitable for engine-compartment mounting.

According to Spencer, the installation was effortless and he accomplished the task in his garage using a flying lead wiring harness, though there are plug-and-play options available from AEM. He worked with the AEM tech staff to get the car started up using their start-up program, which requires answers to a series of basic parameters (displacement, cylinders, ignition type, and firing order) and methods of calibration for ignition and airflow. The software creates a base VE table to get the car fired up easily. Spencer chose to run his Roush Mustang on the Westech chassis dyno, which showed his car was making 608 rwhp with some fine-tuning.

Other Features of the Series 3

The Infinity ECU uses a coolant-temp-based idle control model. It includes an rpm vs. engine-speed-rate idle decel feature that provides accurate control of the IAC and allows for adjustment of engine braking. The Infinity’s idle TPS offset provides smoother low idle operation when necessary, like driving in the pits or return lane following a pass.

Choose from time, gear, vehicle speed, switch based or other boost control strategies. The Infinity’s boost control includes two 2D base duty tables and two 2D boost target tables. The second tables can be used as a trim, and users can choose from multiple strategies including IAT, MAP, Baro (kpa), throttle percentage, flex fuel content, boost target and more. AEM’s forums have an in depth review of the Infinity’s boost-control capabilities.

The Infinity’s software allows you to run a single-stage wet or dry nitrous set up with a four-stage to soon become available. This feature includes nitrous timing delay to account for nitrous bleed out, and can be set up for water/methanol injection tuning. Four stage nitrous will be upgraded for free for existing Infinity users when it becomes available.

The Infinity’s diagnostics software can be configured to constantly monitor signal and current quality to alert the user of a potential issue before it creates the potential for engine damage. And finally, dual knock-signal conditioning circuits allow for precise measurements of knock levels. The Infinity can utilize both piezoelectric and flat-response-type knock sensors.

Real World Results

Instantly the Series 3’s capabilities were realized once Spencer grabbed the transbrake button and brought the car up on the two-step. “Using the CD-7 dashboard data logger and overlaying it with the Series 3 graphs, I was able to clean up the air/fuel ratio and timing when I got the transbrake, bringing the rpm up quicker and keeping the engine consistent when it hits the two-step,” shared Spencer.

He continued, “I’ve gone into the fuel tables to lean it out a bit, allowing the car to get up on the converter quicker and helping the sixty-foot times if I need to push it a bit in Index or Open Comp racing. The Series 3 has given me control that the factory ECU never offered.” The smoother two-step tuning with timing and air/fuel control has produced a quicker reacting racecar. In fact, Spencer said they have to mechanically adjust the transbrake button to slow it down—his worst light at the last race was .007!

Another bonus is the ability to go back and forth between open loop and closed loop using the 02 sensor. Spencer will baseline the car in closed loop mode, meaning the ECU will correct the tune to a target air/fuel ratio. In competition, he will adjust the fuel map to be as close to perfect and then run the car in open loop mode. The locked tune in open loop enables the supercharged Mustang to run near identical from run-to-run, provided the weather doesn’t change too much between rounds of competition.

Then the final benefit is tuning the car to go quicker or slower based on his index, the Series 3 is used to ramp in timing quicker, or slower, and has the car running smoother and more predictable.


AEM Performance Electronics


Mike Galimi
Mike Galimi is the Director of Content & Marketing at ProMedia Publishing and Events with nearly 20 years of experience in motorsport writing and photography.