With the short-block, cylinder heads, valvetrain, and induction installation sorted out, the last step before hitting the throttle is feeding that new LS stroker motor some fuel and spark. This can be achieved by using the factory EFI system, an aftermarket EFI system, or by converting over to a carbureted induction setup. All three methods have their pros and cons, and there are dozens of different options among the three arrangements.
This Tech Tip is From the Full Book, HOW TO SUPERCHARGE & TURBOCHARGE GM LS-SERIES ENGINES. For a comprehensive guide on this entire subject you can visit this link:
SHARE THIS ARTICLE: Please feel free to share this article on Facebook, in Forums, or with any Clubs you participate in. You can copy and paste this link to share: http://www.lsenginediy.com/fuel-and-spark-guide-for-big-inch-ls-engines/
For instance, GM used several different types of factory powertrain control modules, which must be matched with specific engines and wiring harnesses. Furthermore, the stock PCM can be tuned by using specialized programs and a laptop computer, or a simpler hand-held device. Stand-alone aftermarket EFI systems eliminate much of the applicationspecific minutia associated with running a factory PCM, but they’re generally more expensive; however, there are several different manufacturers to choose from.
If simplicity is the primary objective, a carbureted induction system is the easiest to install and tune. Thanks to standalone ignition systems from companies such as MSD and GMPP, LS-series smallblocks can have their timing maps tuned with a laptop while still relying on a venerable carburetor for fuel delivery. Although space limitations here prevent breaking down every single option on the market, here’s a run-down of some of the most popular engine management systems available.
Electronic Fuel Injection
Part of the appeal of building an LS-series small-block for any project car is its high-tech credentials. Electronic fuel injection (EFI) adds to this mystique, and it offers irrefutable advantages over a carburetor in cars that see an appreciable amount of street duty. EFI-equipped motors start up reliably—even in cold weather—and offer improved fuel mileage, cleaner emissions, and superior drivability.
On the other hand, EFI’s impact on horsepower output is a topic of much debate. In numerous back-to-back, EFIvs.-carburetor dyno tests conducted by several highly respected engine builders, a fuel-injection system rarely produces more power than a carburetor. Usually, it’s the other way around, with the carb taking top power honors. That’s because carburetors atomize fuel very high in the intake manifold, which increases charge density and the inertial ram effect of the incoming air/fuel charge.
In fact, this is why Formula One engines have their fuel injectors positioned at the top of the intake manifold runners. In contrast, production engines, including the Gen III/IV small-block, have injectors placed at the very end of the intake runners. Additionally, EFI systems tend to be more temperamental and difficult to tune. These inconveniences aside, no carb can touch the versatility and streetability of a well-tuned EFI system. So although it may take more initial effort to dial in, a properly tuned fuel injection system offers the best balance of all-around performance and economy.
Stock Powertrain Control Modules
The LS-series small-block has only been in production since the late 1990s, but GM has matched it with a dizzying array of powertrain control modules (PCM). Nevertheless, when matched with software programs, such as those from HP Tuners or EFI Live, the factory computer is an incredibly powerful tuning device that can tame even the most radical engine combinations. These software programs offer levels of tuning flexibility similar to that of an aftermarket stand-alone system, and at a fraction of the cost. Just a few years ago, this type of technology was unheard of.
If you are opting for a used-core engine as the basis of a stroker LS project, know that they’re often sold with a matching PCM and wiring harness. This ensures that the engine and PCM are compatible with each other. However, with the increasing availability of aftermarket blocks, not all engine builds start with a used-core engine. If you are electing to run a stock PCM-based engine management system, it’s imperative to choose the right computer. Factory GM computers can be broken down into two basic groups: those designed for 24-tooth reluctor wheels and those designed for 58-tooth reluctor wheels.
Engines equipped with 24-tooth wheels include 1997–2004 LS1s, 2001–2004 LS6s, 2005 and 2006 LS2s, and 1999–2006 Vortec truck motors. Gen IV small-blocks—including the LS3, LS7, LS9, LSA, L76, L99, and 2007-andlater Vortec truck engines—come equipped with 58-tooth reluctor wheels. Generally, either style PCM can be used to operate any LS-series small-block, as long as it’s matched with the correct reluctor wheel and wiring harness. For instance, if you’re using an LS3 core as the basis of a stroker built, it can be paired with a PCM designed to work with a 24-tooth reluctor wheel, as long as a 24-tooth reluctor wheel is installed on the crankshaft.
A major difference between the two is that 24-tooth reluctor wheel PCMs can be programmed to operate both drive-bycable and drive-by-wire throttle bodies, and 58-tooth reluctor wheel PCMs are only compatible with drive-by-wire throttle bodies. Because PCMs designed for 58-tooth reluctor wheels have been produced in much lower quantities thus far, they tend to be harder to find and more expensive. Consequently, the 24-tooth reluctor wheel PCMs are far more popular with LS enthusiasts. They’re plentiful and can be purchased for as little as $50 to $100. One caveat is that the PCMs used on 1997 and 1998 LS1-powered F-bodies and Y-bodies have a different pin-out configuration, which requires a different wiring harness, so they are less common for engine swap applications.
For decades, the only way to comprehensively reprogram a fuel-injected engine was to bypass the stock PCM entirely with a stand-alone aftermarket computer. That all changed in the late 1990s, when computer-savvy hot rodders figured out how to hack into the factory computer codes and fully unlock the tuning potential of stock PCMs. In the LS camp, tuning software from HP Tuners and EFI Live has set the standard for flexibility and ease of use. These systems are essentially software programs that are downloaded to a laptop computer, and they interface with the factory PCM through the diagnostic port. The versatility of these programs is truly impressive, as they allow modifications of the fuel injector pulse widths, ignition timing, rev limits, knock retard, transmission shift points, cooling fan thresholds, speed limiters, final drive ratios, idle speed, and data logging. Additionally, the compatibility with two- and three-bar MAP sensors allows control over extreme-horsepower, forced induction applications.
Because reprogramming the stock PCM can be intimidating, both HP Tuners and EFI Live offer comprehensive support forums on their websites, as well as a stockpile of various tunes users can download to use as a solid baseline program instead of trying to create one from scratch. Prices range from $400 to $800. The factory PCM can also be tuned using hand-held devices from companies such as Superchips, Granatelli, Jet, and Diablosport. These hand-held units plug into the PCM’s diagnostic port, but they do not require a laptop to operate. Most offer generic tunes that alter the fuel and spark maps based on fuel octane ratings, and some allow alterations of shift points, rev limits, and shift firmness. Due to their limited range of flexibility, handheld tuners are best suited for stock or near-stock engines, but not for a heavily modified stroker combination.
Aftermarket EFI Systems
Without question, tuning software, like that from HP Tuners and EFI Live, has pushed the stock PCM beyond what anyone could have imagined just a decade ago. In fact, it’s not unheard of anymore for a 1,000-hp forced-induction engine to make do with a factory computer. Even so, there’s a limit to the stock PCM’s capabilities, which is why you won’t find a single Outlaw drag car running anything but a standalone aftermarket EFI system.
Once eclipsing the 1,000-hp mark, where heavy doses of boost and multiple stages of nitrous are the norm, an aftermarket EFI system offers a level of precision and versatility that a stock computer just can’t match. Obviously, these systems are geared more toward race cars and extremely high-end street cars, but with the tremendous horsepower potential of the LS platform, street cars equipped with aftermarket EFI systems are becoming more common.
There are literally dozens of standalone EFI systems on the market, but the most popular units with LS enthusiasts are offered by FAST, BigStuff3, and Accel. Compared to their stock-based counterparts, aftermarket systems offer more durable injector drivers, traction control, individual cylinder tuning, wideband oxygen sensor compatibility, multiple stage boost and nitrous controls, and data-loggers featuring accelerometers and blazing sampling rates. The biggest downside to these systems is cost, as they ring up a bill between $2,000 and $3,000. That price includes an aftermarket computer, wiring harness, engine sensors, and computer software. For the ultimate in tuning flexibility and horsepower potential, an aftermarket EFI system offers limitless possibilities.
Self-Learning EFI Systems
As computer technology continues to evolve at an alarming rate, it has enabled the automotive aftermarket to develop EFI systems that can now program themselves. Holley has recently launched its Dominator EFI system for LS-series small-blocks, and it offers many of the same flexible tuning features as competing systems. The ace up its sleeve, however, is a self-tuning fuel table that greatly simplifies the tuning process. By utilizing dual-channel wideband oxygen sensors, the Dominator EFI system can precisely create a fuel map based on an engine’s fueling needs within a couple of wide-open-throttle (WOT) dyno pulls. From there, the end user can fine-tune the programming. It’s very impressive technology, for sure, and it offers a glimpse into the future of aftermarket EFI systems.
Fuel Pump and Injector Sizing
Of the multitude of decisions that go into properly planning and building a stroker LS small-block, choosing an appropriately sized fuel pump and injectors is relatively easy. For naturally aspirated combinations, a good rule of thumb to follow is to use a fuel pump that flows .5 lb/hr of fuel for every 1 hp. For example, a 1,000-hp naturally aspirated combination needs a pump that can flow 500 lb/hr of fuel, and a 500-hp engine requires a pump capable of flowing 250 lb/hr of fuel. Because maxing out a fuel system leaves no margin for error, it’s not a bad idea to add another 10 percent of flow as a safety factor. Forcedinduction applications tend to be less efficient, so fuel pump flow rates of .60 to .65 lb/hr per hp are ideal.
Once proper fuel pump size has been determined, selecting the right injectors can be calculated in a similar fashion. A 1,000-hp naturally aspirated engine that requires a 500-lb/hr fuel pump would need 62.5 lb/hr injectors. That’s because 500 pounds of fuel divided by eight injectors yields 62.5 lb/hr per injector. That said, fuel injectors are all rated at a certain fuel pressure, and increasing fuel pressure can bump up the flow rate of an injector. Therefore, it’s important to compare the pressure an injector is rated at to the fuel pressure you will be running in your engine combo when selecting fuel injectors.
Although the Gen I small-block Chevy was built in both carbureted and fuel-injected configurations from the factory, all LS-series motors came equipped with EFI. This presented a problem for traditionalists, as they recognized the horsepower potential of the LS platform, but they didn’t care for the complexity of EFI.
Edelbrock and MSD teamed up to create an ingenious solution in 2003 that allowed a person to bolt a carburetor to the Gen III small-block. Edelbrock got things rolling by creating a series of carbureted intake manifolds for LS-series small-blocks that could accommodate a MAP sensor. MSD then developed a revolutionary new ignition controller that took care of the spark side of the equation. The MSD 6LS controller looks like any other MSD ignition box, but it features a wiring harness that plugs into the coil packs and crankshaft and camshaft position sensors of the LS small-block. That and the MAP sensor integrated into the Edelbrock intake manifold are all that’s needed to manipulate the factory ignition system. The MSD box allows creating custom timing advance maps with a laptop computer and has controls for vacuum advance, rev limits, and a step retard for nitrous use. Furthermore, MSD has two versions of its LS ignition box that will work with both 24- and 58-tooth reluctor wheels. With a carburetor administering fuel, and the MSD box controlling the electronics, for traditionalists, this combo is the best of both worlds.
For good reason, when the topic at hand is the phenomenal performance of the Gen III/IV small-block, most of the talk revolves around the cylinder heads. However, the cast of supporting components, such as the ignition system, shouldn’t be overlooked. As with many modern cars, the LS-series small-block utilizes crankshaft and camshaft position sensors to precisely measure the location of each piston. This allows the ignition system to fire each cylinder at exactly the right moment to maximize power and reduce emissions. Another benefit is that the system eliminates the need for a conventional distributor. In its place are eight coil packs, one for each cylinder, that bolt on top of the valve covers.
With one coil pack dedicated to each cylinder, this coil-on-plug arrangement results in a tremendous amount of spark energy. In fact, the stock ignition system performs reliably in engines producing well in excess of 1,000 hp. The only reason to replace a factory coil pack is if it’s stopped working, due to age. Otherwise, the stock coils can handle just about anything an engine can throw at them. Over the years, GM has produced five different types of coils. Although they look different externally, due to the fact that they’re made by different suppliers, GM says that the performance among them is identical. MSD also offers stock replacement coil packs, which are said to produce three times the spark energy.
Written by Barry Kluczyk and Posted with Permission of CarTechBooks