Total Engine Control for Your LS1

You cannot deny that the LS1 engine is a sweet piece. There probably was never a powerplant, which sat between the fenders of a Pontiac that was so easy to make power with. A simple cam swap and head porting job releases 100 to 120 additional ponies, and that is on top of baseline stock figures of 320-350. What a testament to the prowess of GM engineers!

But as with any modern engine, the key to unlocking the most power from the parts installed lies in the ability to tune the engine-control computer. The industry answered this call with application-specific software such as LS1 Edit that allowed entry to many of the required calibration tables in the factory PCM. But since EFI calibration is a science unto itself, many so-called tuners were only changing the injector flow rate table as an attempt to tune a modified LS1 engine. Even if the tuner had the necessary skills to utilize the full ability of the edit software, there was always some power left on the table using the GM PCM.

Why would that be if the ignition timing and air/fuel ratio are correct, you may ask? There is no denying that the GM PCM is an excellent engine controller, as are all OE systems, but the internal logic is based upon an emissions instead of a performance strategy. The slew rates are designed to keep the EPA happy, not necessarily produce the best performance down a 1/4-mile. To prove that there is untapped power in almost every modified LS1 engine, ACCEL/DFI had racer and ACCEL/DFI dealer, Joe Overton of Lethal EFI Performance, install a pre-production Generation 7.0+ ECM into his already stout F-body and run it down the track. The 1/4-mile elapsed time decreased by 3/10 of a second! When this got back to HPP, we knew we had to give our readers the low down on this great product.

THE ECM
The 7.0+ ACCEL/DFI ECM that is used in the LS1 kit is the same one found in the company's universal applications. Its advanced design allows ignition compatibility and most options to be software selectable. There are additional components that are part of the LS1 kit and they will be covered as the text progresses.

What sets the ACCEL/DFI system apart from its competition is the advanced OE-style logic used by the ECM. The ACCEL/DFI 7.0+ is a math-based engine management system that employs a complex speed-density equation to control the fueling of the engine. This is in contrast to most if not all other aftermarket ECMs that use a look-up or pulse-width table in an attempt to control the injectors.

With a pulse-width designed ECM as was the older ACCEL/DFI 6.0, the tuner places values in a matrix that equate to a fuel injector opening time in milliseconds (1/1000 second). The amount of injector opening is based on only 2 dimensions, engine speed and load, which are measured as a function of manifold absolute pressure (MAP). Though systems of this type can run an engine satisfactorily, their crudeness often does not allow the maximum performance to be obtained. In engineering-speak, a pulse-width system would be said to use 2 degrees of freedom (DOF), rpm and manifold pressure in its decision making process.

In contrast, the advanced 7.0+ ECM uses a 7 DOF mathematical equation. The ACCEL/DFI system references engine displacement, injector size, volumetric efficiency, manifold absolute pressure, number of cylinders, intake air temperature, and desired air/fuel ratio and then decides how long to open the fuel injectors. When tuning the ACCEL/DFI system, the user is actually modeling the amount of cylinder fill, which is represented by volumetric efficiency (VE) along with the desired target mixture ratio.

In addition, functions such as self-diagnostics, advanced data logging, multi-stage nitrous control, ignition and fuel rpm limiters, along with the ability to be configured for either normally aspirated or boosted engines up to 30 psi are some of the 7.0+ features that come with every unit.

As mentioned previously, when tuning the engine, most of the time will be spent in the Base Volumetric Efficiency and Target Air/Fuel Ratio tables. In all, there are up to 100 calibrations screens available to maximize the LS1 engine if the Pro software is purchased. The standard CalMap software limits access to 40 screens and is usually all that is required for a 500 to 550 hp application. This is not to be interpreted that the additional 60 calibration screens from the Pro CalMap software are missing or left out. The only difference is, they function with predetermined values entered by ACCEL/DFI and cannot be altered by the tuner when using the standard software.

The Base VE, Target A/F, and Ignition Timing tables can all be load and rpm scaled to suit the needs of the particular engine. This is an especially nice feature that allows the user to expand the tuning resolution or set points in the areas that the engine operates the most frequently. For instance, if a 2-bar MAP sensor is being used for a supercharged application but the blower only builds 10 psi of boost, there would be no need to have the load scale set to 15 psi. Instead the load can be scaled to maximum of 10 psi and the additional tuning points can be used working up to that value. This allows for the best tune-up to be achieved with minimal effort. An especially interesting and noteworthy feature is the ability to perform individual cylinder tuning of the mixture ratio. Being able to so easily correct for variations in the intake manifold flow and fuel distribution is alone worth the price of admission.

Additional features of the ACCEL/DFI system are software selectable sequential or batch injector firing events along with the installation of the optional wide-band universal oxygen sensor option (UEGO). The kit comes with a standard heated exhaust gas oxygen (HEGO) sensor that mounts in the header or exhaust manifold. This production-style sensor has the ability to recognize an air/fuel ratio of 14.7:1. But the optional wide-band sensor kit allows the ECM to correct to mixture ratios of between 10:1 to 20:1. Especially nice for nitrous applications, the wide-band feature has the ability to let the ECM track the mixture ratio. If the air/fuel ratio goes leaner than the user programmed mixture, the 7.0+ system automatically shuts off the nitrous. This may cost you the race but will save the engine to race another day.

THE KIT
As with all ACCEL/DFI engine management systems, the 7.0+ is American-made and built to rugged OE-quality standards in an ISO certified facility. Cataloged under PN 77050 the complete kit has a retail price of $2150 and includes everything required to switch an existing EFI car to the ACCEL/DFI.

The ECM is considered weatherproof and can be mounted either in the vehicle or under the hood. This is not to be confused with waterproof that would allow submersion. The ECM is not completely sealed because of an internal barometric pressure sensor that is used to keep the engine performing perfectly in all weather conditions. The barometric sensor needs to experience atmospheric pressure. For a hassle-free installation, the wiring harness has an integral fuel pump relay and employs weather tight connectors.

ACCEL/DFI takes much pride in the fact that not only is the 7.0+ ECM the most advanced engine controller in the aftermarket, but the kit was designed to be a direct plug-in to all of the GM sensors and underhood wiring. To work with the LS1's coil-on-plug ignition system, an additional LS1 module is included in the package. This component is used to drive the 8 ignition coils on demand from the ACCEL/DFI ECM. When installing the ACCEL/DFI ECM the factory issue 8-way injector and ignition coil harness is retained.

The ECM is enclosed in a rugged extruded aluminum case and can be connected if so desired to work in concert with the factory PCM. Many street car applications choose to use the ACCEL/DFI as a companion engine controller, allowing manipulation of the fuel and timing commands. If connected in this fashion, mundane duties such as cruise control, transmission logic, etc. are all left in tact.

As with other ACCEL/DFI 7.0+ products the LS1 kit is sold only through the company's nationwide network of more than 200 Engine Management Installation Centers (EMIC). This group of highly trained dealers can provide whatever level of service the Pontiac hobbyist desires. This ranges from an over-the-counter sale to a complete installation and calibration.

Not only does the ACCEL/DFI allow fine tuning of a modified engine but it opens up the possibility of an easy engine swap of LS1 power into any Pontiac body style. So if you are one of the many F-body owners who are looking for the maximum from your Bird, then give ACCEL/DFI a call and let those Ponchos run!

EFI FOR EVERYONE
There is no need to run out and buy an LS1 car to enjoy the benefits of ACCEL/DFI electronic fuel injection. The same features are available on the standard kit and at a lower cost because there is no need for a special coil driver module. ACCEL/DFI offers part numbers for both L98 and LT1 engines. In addition, ACCEL/DFI sells all of the parts required to turn a "Pure Pontiac" engine into EFI. Electric fuel pumps, weld-in injector bungs, raw stock fuel rail, fuel injectors, high flow-four-barrel-style throttle bodies, along with all the necessary sensors are in the ACCEL/DFI catalog. Also offered are a complete line of crank triggers, CD ignition boxes, and electronic spark timing distributors to round out the product line.

Since Mallory is part of the Mr. Gasket Performance Group, the parent of ACCEL/DFI, an especially interesting Pontiac distributor for EFI is now on the market. Identified as the Dual-Sync, it incorporates both an internal cam and crank trigger signal so a real Pontiac engine can not only be converted to EFI, but true sequential firing of the injectors. By opening the fuel injectors in time with the valve events instead of all at once as batch fire does, it provides better hydraulic control in the fuel rail along with improved fuel injector performance. One long pulse width of the injector is better than 2 short pulses. The longer opening time allows the injector to become more repeatable and atomize the fuel better.

Even though a Pontiac engine can run great with a properly tuned carburetor, do not discount the benefit of adding ACCEL/DFI 7.0+ EFI to your ride.