ACCEL Gen 7 System - Magnum Returns

It's long overdue, but we finally got everything to come together in the engine room of our long-term third-gen project car, Magnum TPI. We'll let the photos tell most of the story, but if you want to bone up on the first three parts of our 396 stroker build up, we suggest you reference the September 2001, November 2001 and January 2002 issues (see "Pumping Up," parts 1, 2 & 3, respectively). Here, we're dealing strictly with the engine management portion of the project, but we still need to acknowledge the contributions of Lunati (rods, pistons, bearings, rings, oil pump), Cola (forged crank), AFR (cylinder heads), Comp Cams (cam, valvetrain), ACCEL (SuperRam intake, throttle body), Evans Cooling (cooling system), Be-Cool (cooling fans), Royal Purple (lubricants), and Strope Speed Shop (engine assembly and installation).

The big news here is DFI's new Gen 7 engine management system. It offers the sophistication and flexibility of Detroit's most advanced engine control systems combined with the programming ease of a Windows-based program. This ease of programming is significant, because to make max power in a street engine like our 396, it's just not practical, or even possible, with 14-year-old electronics. Not only is the Gen 7 a performance breakthrough--incorporating the latest in wide-band 02 technology--but as you'll see, it's got a scandalously low price too. (For more on the DFI Gen 7, check out "Better By Design" in the October 2002 issue.)

The other big breakthrough is Fast Track Performance's jumper wiring harness. This piece allows our factory ECM to control all emission functions just as it did when our car rolled off the assembly line--and it can for you too, provided all your smog gear still exists and operates properly. Essentially, Fast Track's harness allows an aftermarket computer such as the DFI to run the engine while the OEM computer runs the smog gear. It's an elegant solution to a difficult problem, especially for street-legal cars in smog-controlled states like California and New Jersey.

The final piece of the puzzle was finding a qualified engine management installation center like Second Street Speed to do the dyno tuning. These guys know how to make cars run and have some of the fastest EFI cars on the east coast running out of their shop. When Magnum TPI finally came under the gentle electronic tutelage of Second Street's Bill Hunsberger, we knew we were seeing the light at the end of the tunnel.

As you'll see, Hunsberger got us hooked up, dialed in and tuned up with Second Street's vast array of gear, including its wide-band monitor, CDS data acquisition and Dynojet chassis dyno. It also offers complete engine building services, a state-of-the-art SuperFlow 1020 flowbench and a SuperFlow engine dyno equipped for fuel injection, so if you've got a truly hairy GM-powered street car in need of attention, give Second Street a call--they can handle it.

We did uncover some expected airflow limitations which cut substantially into our power, but at least we can hang a real number on it and get it fixed for our next trip to the track. Even with the restriction of the factory air intake ductwork and MAF housing, we managed a respectable 12.30/109.4 in the summer heat at full weight. As demonstrated by the Second Street dyno, there's another 30 rearwheel horsepower waiting for us with a proper inlet tract, so we are definitely within reach of running 11s on pump gas with catalytic converters and a smog-legal tune. Check out the accompanying photo captions for the entire story.

To solve our calibration dilemma, we turned to ACCEL's new Gen 7 system. This system has many benefits over the stock ECM including sequential injection, data logging capability, dual mapping, auto-adjusting low- or high-impedance injector driver circuits, wide-band O2 control, selectable ignition reference, a Windows-based operating system with pull-down menus, programmable ignition rev limits and fuel cutoffs, converter lock-up and A/C clutch control, nitrous control, and many other programmable goodies.	The Fast Track Performance jumper harness is not necessary for all applications, but we would recommend one if there are tight smog laws or tough dyno emission tests in your state. The Fast Track unit allowed us to retain the factory ECM so that it could continue to operate all emission-related components such as EGR, canister purge and smog pump, and retain all factory diagnostic functions through the ALDL and SES indicator. (It's important to note that the DFI Gen 7--like all other stand-alone systems on the market--does not have provisions to control any smog equipment.) All Fast Track jumper harnesses are made to order and include a sequential injector harness (the factory GM harness is batch fire), a MAS to MAP conversion harness, the adapter harness, the conversion box and installation instructions. Our unit cost $738 and took about four weeks to deliver. Was it worth it? We passed New Jersey's tough ASTM 5015 dyno emission test--with plenty of room to spare--on the very first try.	A basic DFI Gen 7 system for an L98-style TPI motor like ours retails for $1,422. We upgraded to wide-band 02 control for an extra $951, bringing our DFI's total suggested retail (your price will likely be lower) to $2,373. That's a lot of dough, but when you compare it to comparable systems with wide-band control, it's a bargain, and that's not taking into consideration the DFI's ease of use. The large aluminum box with wiring harness in the lower left is a Fast Track Performance jumper harness, not included in the DFI system.
This is a comparison of the standard (HEGO) O2 sensor included in the basic Gen 7 DFI on the left, and the wide-band linear (UEGO) 02 sensor on the right. The rest of the wide-band option (not shown) includes a harness and calibration module calibrated to the specific sensor in the kit. For very high horsepower blower, turbo or nitrous motors, the wide-band can save an expensive engine by compensating with extra fuel when needed. The DFI's wide-band option allows the sensor to monitor and make modest adjustments to fuel delivery in real time in the event your engine goes lean (such as when a fuel pump or injector goes bad in the middle of a run). The standard HEGO sensor is only accurate at precisely 14.7:1 air-fuel ratio; the wide-band is accurate to 3 or 4 points on either side of stoichometric.	How you mount your DFI is up to you, but Strope Speed Shop elected to install our Gen 7 in a dry, protected location under the front passenger seat. The Fast Track harness box occupies the space formerly taken by the stock ECM behind the passenger-side dash panel. The harness runs under the carpet, away from prying eyes; the stock ECM now resides under the rear passenger-side seat cushion. We specified long harness extensions when we placed our order from Fast Track because we wanted both controllers inside the cockpit. Note the DFI interface cable that allows the Gen 7 to be programmed by a laptop or desktop computer.	One of the most striking improvements over the previous Gen 6 DFI is the virtual analog instrument panel. The Gen 7's virtual gauges are a big improvement over digital numerical readouts (which change too quickly to be read) or scalar graphs (which are too small). With traditional gauges the data can be easily interpreted at a glance, thus speeding the tuning process. Note that the air/fuel ratio is a large read-out, dead center in the screen. There should be no doubt about what the most important tuning parameter is!
One of the first screens you'll visit when programming your Gen 7 is this one, the engine configuration editor. The Gen 7 begins earning its keep from the start with this screen, which asks for basic information about your engine such as displacement, number of cylinders, compression ratio, injector size and type, ignition reference and firing order. Once this screen is configured, the software calculates a volumetric efficiency (VE) table from the information. This is significant because in the past the VE table, or load table as it's often referred to, was arrived at through a dismal process of trial and error that could quite often lead to engine damage. The Gen 7's calculated VE table takes the guess work out of fuel programming because instead of inputting injector pulse values directly into cells, the Gen 7 automatically calculates the injector pulse values from the VE numbers. And best of all, the VE table is usually right on the money if you've configured your engine properly. As with all the Gen 7's tables, this can be manually tweaked if desired.	Those familiar with engine dynos will feel right at home with VE (volumetric efficiency) nomenclature. Each cell in the VE table represents--at that engine speed and load--the ratio of actual air/fuel charge in relation to the theoretical maximum allowed by its full, swept volume. The vertical axis is manifold pressure in kilopascals; the horizontal axis is engine rpm. You'll note that unlike the engine dyno, there are many values considerably below 100 percent (1.00). These lower values represent part-throttle conditions. These VE values are used by the processor to calculate the injector pulse time in conjunction with other values such as coolant temperature, ambient air temperature, idle air control disposition and Tau, the manifold puddling constant. As you can probably tell, this fueling strategy is significantly more sophisticated than previous generations of aftermarket engine management. In fact, it's closer to a modern OEM computer in terms of precision, flexibility and processing speed, but with one difference--you can actually tune it without GM's Powertrain department at your disposal.	The target air/fuel ratio map is the key to max power and emissions, and functions in DFI versions with and without wide-band 02 control. In standard versions, the A/F target is reached based on a calculation of the air entering the engine. The Gen 7 then delivers a corresponding amount of fuel to meet this theoretical target. In Gen 7s with the wide-band option, a target is achieved by measuring the A/F ratio directly. In naturally-aspirated engines, the A/F target map usually doesn't vary significantly from one engine to another; DFI offers several generic maps as starting points; ACCEL's tech department can recommend one for your particular engine or help you develop one for a boosted engine.
The ignition map is pretty much the same in all aftermarket engine management systems, including the new Gen 7. The vertical axis is engine load expressed as manifold pressure; the horizontal axis is engine speed. Once again, DFI offers several generic maps to help get you started, but the significant thing to remember here is that spark lead time is highly dependent on combustion chamber efficiency. The better the swirl and quench characteristics of the cylinder head, the less spark lead time and the more horsepower you will make. Note that the Gen 7 does support knock retard like most modern OEM systems. In our application, knock retard is not currently being used because our Evans cooling system has given us an added measure of octane tolerance, but we could implement it in the future if we desire.	One of the pull-down tables we used early on was the idle air control (IAC) throttle follower. This allowed us to set the IAC threshold high enough to keep the engine from stalling when the throttle shuts suddenly. At lower load conditions, the IAC is progressively closed to achieve idle sooner. Later, we discovered the engine would stall when the A/C was on and the throttle was suddenly closed. We then accessed another pull-down menu and programmed 10 more IAC counts to kick in whenever the A/C clutch was engaged. This eliminated the stall with just a few keystrokes.	The CalMap's "help" system is chock full of important information, such as this explanation of the manifold puddling constant, or Tau. Unlike its predecessors or its contemporary competitors, the Gen 7 appropriately adds or subtracts fuel--in a transparent background calculation--based on the amount of fuel available in the manifold that has collected, or puddled, on the manifold walls. (Veteran DFI tuners who have in the past struggled with mysterious part-throttle stumbles will rejoice at the Gen 7's Tau calculation.) Simply put, there is a transient amount of fuel which collects on the manifold walls. This fuel will eventually be used in the combustion process. Furthermore, the quantity of this fuel changes dynamically as load condition and engine speed changes. By knowing the amount of puddled fuel residing in the manifold at all times, the Gen 7 can compensate, thus driveability is vastly improved.
For dyno tuning our Gen 7 DFI, we moved our project car over to ACCEL EMIC Second Street Speed in Perkasie, Pa. Second Street is well-versed in DFI installation and tuning; its capability is often called upon by the east coast's quickest and fastest EFI racers, some of them running well into the 6s in the quarter mile. Bill Hunsberger dynoed Magnum TPI with the stock computer and MAF sensor in place, but not until he had fully wired us up for comprehensive data acquisition including fuel pressure and stand-alone wide-band air/fuel ratio monitoring. With a custom PROM programmed for our 396, the Dynojet registered 226 rwhp. In just a scant few hours, Hunsberger re-installed our Gen 7 (relegating the stock ECM to smog duty), tuned our Gen 7 and uncorked a bucket full of power.	One of the first things Hunsberger does in all his dyno sessions--no exceptions--is to verify the integrity of the fuel delivery system. This CDS data acquisition graph shows how our Cotton's Performance fuel pump was delivering the goods well up to redline. Many times Hunsberger has diagnosed a WOT power problem as an inadequate fuel pump or pump wiring fault. No problem here.	Big problem here. After getting the DFI up and running, power increased to just 323 rwhp--a lot more, but well short of what we already knew this Strope Speed Shop 396 was capable of. The culprit was thought to be a restriction in the inlet ducting, most notably in the rubber elbow and MAF meter. Note that the MAF meter was strictly along for the ride in DFI trim; we wanted to quantify the DFI's improvement without improving airflow, and we also needed it as part of our plumbing.
In our final set of Dynojet pulls, Second Street pulled the MAF sensor and inlet elbow. Power swelled to 354 rwhp, an increase of over 30 rearwheel horsepower; with our automatic transmission and high-stall converter, that's on the order of 40 flywheel horsepower. Obviously, we can't go racing with an open hood and no air filter, so our next goal will be to find a way to get unrestricted quantities of cool, filtered air into the engine. When we figure out how to do that, we'll let you know.	For our drag testing, we went to Englishtown during the GMHTP shootout. We put the air filter, MAF sensor tube and rubber elbow back on (in 323 rwhp trim) and ran a best of 12.30/109.4 with a 1.67 60-foot time. (Weather conditions were 86 degrees, 39 percent humidity and 29.27 baro.) We borrowed TGOW's Mickey Thompson ET Streets and Centerline Telstars and filled the tank with 93 octane. Race weight on this day was 3,625 lbs. with driver. If we can get unrestricted quantities of air into the 396 (getting our other 30 rwhp back), we should nudge the 11.90s in the summer heat and maybe 11.70s in really good air.