In the most basic terms, electronically controlled engines must be carefully calibrated to take advantage of engine modifications that affect airflow and fuel delivery requirements. That is more imperative for forced-induction engines, which process significantly more air than a comparable, naturally aspirated engine—and do it under positive manifold pressure.
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The various calibrations, whether adjusting fuel and spark delivery or “telling” the controller about new injectors or sensors, fall under the broad heading of tuning. The importance of accurate, pinpointed tuning changes all boils down to a central goal: optimizing fuel and spark throughout the RPM range and under all load conditions.
All of the other changes and adjustments to the engine controller’s programming circles back to maintaining a safe air/fuel ratio. Too little fuel leads to a lean condition that can lead to detonation, burned pistons, and worse
Experienced tuners “sneak up” on a supercharged/turbocharged engine’s programming, keeping the fuel mixture rich and spark timing conservative at first. After establishing a safe zone of performance, the air/fuel mixture is refined to maximize horsepower. It can be a painstaking process with many adjustments. Novices are advised not to experiment with their newly force-fed car, as incorrect tuning can quickly lead to expensive problems with an engine under boost.
There is far more to engine tuning and computer programming than found in this single chapter, which covers the basics of what’s involved in the procedures and requirements for forced-induction combinations. For a more in-depth look at tuning, I recommend Greg Banish’s detailed books Engine Management: Advanced Tuning and Designing and Tuning High-Performance Fuel Injection Systems as excellent guides (go to www.cartechbooks.com for more information).
Custom tuning for a forcedinduction system (beyond uploading the pre-programmed tune included with a kit) requires experience and isn’t advised for the novice. It is best to seek a knowledgeable tuner who uses an engine chassis dynamometer facility for accurate, safe tuning. WARNING: Do not start or drive a newly supercharged or turbocharged engine with higher-capacity fuel injectors if the controller is not programmed for them.
Air + Fuel = Horsepower
Of course, the entire reason for adding a supercharger or turbocharger is increasing the airflow through the engine. And with more air, more fuel is required it to maintain an optimal air/fuel ratio across the RPM band. If sufficient fuel isn’t added as RPM and boost increase, the engine runs lean, possibly leading to detonation or worse—burned pistons or catastrophic engine failure.
The factory engine-control systems of LS-powered vehicles ensure optimal combustion, based on a programmed set of engine parameters, including displacement, the size of the throttle body, the capacity of the fuel injectors, and even the specifications of the camshaft. Anything done to the engine that significantly alters the engine’s parameters, from a simple cam change to 10 pounds of boost, requires updated programming. Otherwise, the controller “fights” the changes, as it tries to deliver fuel based on its program.
Without question, a supercharger or turbocharger system radically alters the parameters of the engine’s airflow and manifold pressure, so the controller’s programming must be altered to directly feed the engine more fuel. In a nutshell, that’s the goal of tuning. However, a few clicks of the keyboard are not the only way to produce great horsepower in a safe manner—the fuel system must support it. That means the fuel pump and injectors must be matched to deliver fuel at a rate matched with the engine’s airflow.
To put it simply, without sufficient fuel to match the boosted air charge from the blower or turbocharger, all the tuning tricks in the world won’t produce safe, sustainable performance.
Mass Airflow vs. Speed Density
To ensure the engine receives the precise amount of fuel it needs to match the incoming air, the engine controller relies on an air-metering system. There are two basic types: mass airflow and speed density. From the factory, LS-powered vehicles come with a mass airflow system.
In the simplest explanation, mass air systems directly measure air, while speed density systems estimate it from a variety of inputs. Mass airflow systems use a sensor to provide a direct reading on airflow through the intake tube, ahead of the throttle body. Basically, the sensor tells the controller how much air is entering the engine and the controller responds by matching that airflow with the appropriate amount of fuel. With a speed density system, there isn’t a direct reading of airflow, but it is calculated based on a variety of inputs, including manifold pressure, RPM level, and air temperature.
The boosted air charge of a force-inducted engine requires not only a matching increase in fuel, but the engine controller must be programmed with the specifications of the new parts in order to control the fuel delivery. Inaccurate programming prevents the engine from performing to its full potential or, even worse, allows an unchecked lean condition that could damage the engine.
One of the benefits of a mass airflow system is its ability to roll with certain airflow changes without major tuning alterations. If the increased airflow is within the air meter’s sensor range, it simply signals the airflow reading to the controller, prompting increased fuel delivery (assuming the fuel system is up to the task). That’s not the case with a speed density system, which requires tuning updates for all airflow changes. Also, mass airflow systems compensate for engine wear over time.
Generally speaking, the factory mass airflow systems work with lowboost forced-induction systems and has helped make LS-powered vehicles among the easiest to tune for great power increases. Factory mass airflow systems provide excellent performance and optimal air/fuel for up to approximately 15 pounds of boost. In fact, the pre-programmed, uploadable tuning software that comes with most bolt-on blower and turbo kits is designed to work with the factory mass airflow system and provide good drivability and performance.
The factory mass airflow meter/ sensor assembly is used without modification on most Roots- and screw-type supercharger kits. Largerdiameter meters allow more air, but slightly diminish maximum boost. Changes to the meter’s diameter or the sensor must be addressed in the controller’s programming.
The custom intake systems of most centrifugal supercharger and turbocharger systems require swapping the stock mass airflow sensor into the intake tract. For the most accurate airflow readings, the sensor should be placed in a section of the intake that allows a straight flow path across the sensor element.
The bypass valve (lower left) for a centrifugal supercharger system mounted on a C6 Corvette is shown with the front fascia removed. When installed on a vehicle with a factorystyle mass airflow system, the bypass valve must be mounted between the intercooler outlet (flowing toward the engine) and before the mass airflow sensor. The intercooled air charge must only pass the mass airflow sensor once, or accurate air metering is impossible. That means bypass air shouldn’t be introduced back into the intake stream ahead of the air meter; and bypass air released to the atmosphere shouldn’t be vented after the air meter.
Most modern Eaton superchargers and twin-screw compressors have an integrated bypass valve, negating the need to insert a separate bypass valve in the intake system.
Speed density air metering is the way to go with racing engines, because, generally speaking, it can be programmed to handle more power than a mass air-metered engine. It is also necessary on setups like this twin-turbo engine, where air enters the intake plenum in two places and uses multiple throttle bodies.
After 15 pounds of boost, tuning becomes difficult with factory mass airflow systems because the manifold absolute pressure (MAP) sensor cannot provide accurate readings to the controller. Swapping the stock, 1-bar MAP sensor with a 2-bar or 3-bar sensor alleviates that problem.
Some builders prefer speed density systems with higher-boost combinations, because they aren’t limited by the range of the mass airflow sensor. They also enable higher boost with 1-bar MAP sensors. However, speed density systems have “fixed” programs, meaning that the controller is programmed to suit the exact parameters of the engine to ensure the air/fuel ratio. Anything done to the engine that changes the airflow characteristics, or volumetric efficiency, requires a new program for the controller—and that goes for engine wear over time and, sometimes, extreme temperature swings. Also, drivability can suffer somewhat, when compared with a properly tuned mass air system. Generally, however, speed density systems are used more with very-high-boost/racing combinations, where stoplight-to-stoplight smoothness isn’t a great concern.
Bottom line: For most street and street/strip combination of low to moderate boost, the factory-style mass air system is preferred.
Map Sensors
Whether used with a bolt-on kit on an internally stock engine or on a custom-built engine, a MAP sensor that’s capable of “reading” higher levels of boost must be used. Forcedinduction engines making approximately 8 to 10 pounds of boost usually work fine with the 1-bar MAP sensors that are equipped on most naturally aspirated LS production engines.
When the boost level is expected to exceed 10 pounds, at least a 2-bar MAP sensor should be used. The 6.2- liter LS3 engine uses a 2-bar pressure sensor, while the LSA and LS9 use a trio of sensors—one on the inlet side before the supercharger, and two on the outlet side, after the supercharger and intercooler. The LS3 sensor, along with the inlet sensors for the LSA and LS9, are the same GM PN: 12591290. The outlet sensor on the factory supercharged engines is a 2.5- bar MAP, PN 12592525.
The MAP sensors for LS engines are mostly interchangeable, except for the LS7 sensor. Here’s the factory 2-bar sensor for LS9/LSA engine. Adding a higherpressure sensor must be accounted for when programming the controller.
The three factory MAP sensors are visible on this LSA engine. For the most part, aftermarket supercharger systems use only the single MAP sensor from the stock, naturally aspirated engine. If the system is tuned to produce more than 10 pounds of boost, the factory 1-bar sensor should be swapped with at least a 2-bar MAP sensor, and the flash memory for the controller must be updated to accommodate it.
The 2-bar sensors are interchangeable with 1-bar sensors, but the engine-control module must be modified to reflect the change. For experienced tuners, it is a quick and easy adjustment. The recommended sensor is the more common PN 12591290 part. The only factory LS-engine MAP sensor that doesn’t directly swap out with the others is found on the naturally aspirated LS7. Its sensor has a different-size pin end.
There are aftermarket 2-, 3-, and 4-bar MAP sensors, but for most higher-boost combinations, the GM 2-bar sensor is adequate.
GM Controllers
Generally speaking, all of GM’s production LS engine controllers can be tuned to work with supercharged and turbocharged engine combinations. Commercial tuning is available for all of them and each works well with low- and moderate-boost systems.
GM’s E38 and E67 controllers are the most flexible for tuning of those matched with factory LS powertrain systems, with the E67 being the best for forced induction. For higher-boost engine combinations that also incorporate other significant engine modifications, it is the best choice for tuning up to approximately 1,000 hp. It is available through GM Performance Parts, under PN 19166569.
The later E38 and E67 controllers are the most flexible, offering greater parameter ranges, but the E67 is the most flexible of them all. For highboost, custom-engine combinations, it is the best option—to a certain point (see page 94, “Standalone Control Systems”). It is available from GM Performance Parts under PN 19166569.
Here’s a quick look at the most common factory controllers used with LS engines.
LS1A: Used on early LS1 engines equipped with a cable throttle and 24X reluctor wheel. Also features integrated transmission control and a wiring harness with LS1 fuel injector connectors.
LS1B: Used on later LS1 engines and compatible with electronic throttle control with separate throttle actuator control (TAC) module, and a 24X reluctor wheel. It features integrated transmission control and uses LS1- style injector connectors.
E40: Not as common as the LS1 controllers or the later E38 and E67 controllers, the E40 works with a 24X wheel and electronic throttle control, but the harness uses LS2- style fuel-injector connectors; no integrated transmission control.
E38: Works with a 58X wheel and electronic throttle control; uses LS2-style injector harness and compatible with integrated, automatic 6-speed transmission control.
E67: Same basic capability as the E38: 58X, electronic throttle, LS2 connectors and integrated 6-speed automatic transmission control—but with a greater range of parameters and increased tuning flexibility. It is the controller used with the factory LSA and LS9 engines, along with several other naturally aspirated LS engines.
It’s important to note that the later controllers, including the E38 and E67, were incorporated based on vehicle and system requirements, so different LS-powered vehicles built in the same model year were equipped with different controllers. The 2010 Camaro SS, for example, was equipped with the E38 controller, while the same-year Cadillac CTS-V received an E67. In other words, the next-generation controller didn’t necessarily supersede the previous generation in production vehicles—different vehicles received different controllers based on their control-system and vehicle electrical architecture.
Pre-Packaged Programming
The vast majority of supercharger and turbocharger kits include some type of uploadable, pre-programmed tuning system, usually a hand-held device that plugs into the vehicle’s OBD (on-board diagnostics) port beneath the dashboard. When the instructions are followed correctly, the engine controller has all the information it needs to operate the engine safely. For do-it-yourself enthusiasts and those without convenient access to independent tuning shops, it’s the only real option for tuning the car.
Because a measure of safety is built into those pre-programmed systems—ensuring adequate fuel delivery and spark control for a number of variables including fuel type, engine load, altitude, and more—it is possible to achieve greater horsepower results with custom tuning. More importantly, the pre-packaged tuning cannot be used if other major engine modifications have been made, including a camshaft swap, stroker crankshaft, higher-flow cylinder heads, or even fuel injectors of a different capacity than what was included with the kit. To put it simply: Anything beyond the blower kit is not accounted for with a kit’s included programming.
GM’s E38 and E67 controllers are the most flexible for tuning of those matched with factory LS powertrain systems, with the E67 being the best for forced induction. For higher-boost engine combinations that also incorporate other significant engine modifications, it is the best choice for tuning up to approximately 1,000 hp. It is available through GM Performance Parts, under PN 19166569.
Flash tuners upload their programming to the engine-control module or powertrain-control module via the OBD-2 port located inside the vehicle, under the dashboard.
Some manufacturers have technical hotlines that allow custom tuning, but the modifications beyond the stock configuration must be conveyed before the kit is shipped. (See page 93, “Livernois Motorsports’ X-Treme Cal Tuning System,” for an alternative.)
Aftermarket Flash Software
One of the reasons LS-powered vehicles are so popular among high-performance enthusiasts is the comparative ease with which their controllers can be reprogrammed to accommodate the air/fuel changes that come with engine modifications. Aftermarket software packages enable professional and knowledgeable private tuners to edit and/or alter the operational parameters of the enginecontroller program and upload the changes through a flash procedure.
The ability to alter the flash memory of engine controllers is a big change from earlier computercontrolled systems that used control-module “chips” that required separate ones to be “burned” for basically every modification. All LS-powered production vehicles use the modern flash-style memory systems that are easily accessed via the OBD-2 (onboard diagnostics, second generation) port under the dashboard.
The primary sources for LS-engine flash memory tuner software utilities are HP Tuners EFILive and Carputing LLC, a company whose products are collectively known by the name LS1 Edit. Like software for a home or business computer, the utilities offered by these companies are licensed either on a singular basis for a specific vehicle or for tuning shops that use the software for multiple vehicles. They are priced accordingly, too, with single-vehicle systems costing several hundred dollars and multiple-vehicle licenses costing several thousand dollars.
Here’s an example of an editable screen from HP Tuners’ flash memory utility. When the tables are adjusted, the settings are saved and uploaded to the engine controller. It then directs the engine and/or transmission as programmed. Knowing which values to change and what to change them to is the trick of tuning. An understanding of how the values affect the engine and transmission is necessary before modifying them.
This is an HP Tuners interface module that connects between a computer and the OBD-2 port inside the vehicle. It is what enables modifications in the flash memory to be made, saved, and uploaded. Whether using HP Tuners’ system or the LS1 Edit system from Carputing LLC, software is included to facilitate modifications.
Lidio Iacobelli, from Alternative Auto Performance, performs a common test-and-tune procedure, whereby a test drive of a modified vehicle determines the need for further tuning adjustments. With a laptop connected to the HP Tuners interface and plugged into the OBD-2 port, Iacobelli inputs the value changes and saves them to the controller’s flash memory. Then, it’s out for another test drive to find out whether the changes delivered the desired results.
Boiled down to their most basic functions for tuning, these products enable the user to read the engine controller flash memory and save it to a file that can be altered/modified to suit new performance and engine component parameters. HP Tuners’ VCM Editor utility, for example, enables manipulation of not only fuel and spark parameters, but RPM limit, cooling-fan operation, transmission shift points, and more. It also incorporates an automatic recovery feature that protects against re-flashing problems.
Currently, HP Tuners’ latest tuning utility is VCM Suite 2.22, which incorporates updated Editor features along with the company’s VCM Scanner. System highlights include:
- Windows Vista compatibility
- “Tunerlock” support for GM’s E38 controller (preventing access by unauthorized tuners)
- More than 450 updated parameters for GM’s 6L80 automatic transmission (along with Alison transmission and Duramax Diesel engine support)
As with HP Tuners, the editing utilities from Carputing LLC (LS1 Edit and LS2 Edit) enable manipulation of the controller’s flash memory. The LS2 Edit utility, which covers most later-model LS-powered vehicles, regardless of whether they actually have an LS2 engine, accommodates those vehicles’ split powertrain controller system that operates on a controller area network (CAN). That means the engine and transmission controllers perform mostly independently, but are linked via the CAN.
Regardless of the utility, you must have a working knowledge of the base fuel, spark, and air/fuel ratio requirements of the engine, recognizing them in the myriad of tables the flash tuner software is equipped with and the proper approximate values for tuning the system to accommodate new performance parts.
This is where a book like Greg Banish’s Engine Management: Advanced Tuning becomes essential. Both HP Tuners and Carputing, LLC, offer online assistance for basic tuning issues and troubleshooting. Many popular online enthusiast forums, as well as HP Tuners’ Web site, devote space to flash-memory tuning. If you are contemplating custom tuning for the first time familiarize yourself with the basics, because even a relatively small mistake at the keyboard could result in serious engine damage.
Livernois Motorsports’ X-Treme Cal Tuning System
Enthusiasts who perform installations at home or don’t have convenient access to a good, reputable tuning shop are challenged when it comes to proper tuning on a combination that exceeds the parameters of a manufacturer’s pre-packaged programming, such as a cam-andheads swap in addition to a bolt-on blower kit. As noted earlier, the flash memory upgrade included with most bolt-on systems does not account for additional engine modifications.
Livernois Motorsports’ solution is an interface system that allows an easily uploadable, customized flashmemory upgrade based on an individual’s specific requirements. It’s called X-Treme Cal Tuning Interface and it essentially works like this: The customer receives the interface kit from Livernois Motorsports, which includes a pre-programmed tune based on that customer’s specific vehicle equipment—a 2009 Pontiac G8 GT with a Magna Charger blower kit, LS3 cylinder heads and a hotter camshaft, for example. Based on the experience of similar combinations, Livernois Motorsports creates an appropriate tune and loads it on the interface module. After receiving it, the customer uploads the new tune to the controller, just as he or she would with the pre-packaged tune from the supercharger kit.
Livernois Motorsports’ X-Treme Cal Tuning Interface includes a software disc, interface module, and cables required to connect between a laptop computer and the OBD-2 port
Among the benefits of the X-Treme Cal Tuning Interface system is how Livernois Motorsports stores each customer’s tuning files. This allows them to quickly modify and forward a revised tune if further changes are planned for the particular engine combination.
“It allows us to achieve results equivalent to dyno tuning for simple bolt-ons or more elaborate power adders that normally would require custom tuning at our dyno facility,” says Livernois Motorsports’ Dan Millen. “The X-Treme Cal Tuning Interface is a single VIN unit with the ability to data log, so it is the customer’s to keep. We can send updates to the customer with our tuning files as they become available, or the customer can update his own tune— within reason—to accommodate further modifications.”
According to Millen, the X-Treme Cal Tuning Interface reads the factory controller program, which can be saved, to return the vehicle to stock specifications. The system includes software, a USB-to-laptop computer cord, and an OBD-2 interface cord.
Standalone Control Systems
Although very adaptable to tuning, the factory controllers on GM vehicles have their limits. In general terms, it’s about 1,000 hp. After that, the requirements to fuel the engine demand things the factory controller isn’t designed for. Mostly it’s injector-driver control, because the high-output, aftermarket-performance injectors are known as the “peak and hold” type and GM’s controllers aren’t designed to operate them.
Joe Alameddine, of ACCEL/DFI provides a more thorough explanation: “Most of the injectors found in the market today that flow significant amounts of fuel for high-horsepower applications are typically low-impedance injectors [less than 12 ohms]. The injector drivers in the stock computer do not support the current levels necessary to drive them properly. Also, the few, specialty highimpedance injectors that are available have a very slow opening rate that causes poor stability at idle and high RPM. The effect is magnified further if the user increases fuel pressure. With an aftermarket computer, such as ACCEL/DFI Gen 8, these issues are not a problem, as each injector driver can handle up to 8 amps. This equates to very finite control at just about any engine speed and compatibility with an injector carrying an impedance rating of 1.5 ohms.”
The ACCEL/DFI Gen 8 engine-control module is one of the most advanced engine controllers on the market and is capable of driving a variety of highperformance fuel injectors. It can fire up to eight ignition coils simultaneously. It features three integrated microprocessors capable of supporting engines spinning to 15,000 rpm and producing more than 3,000 hp. Additional highlights include: the capability to drive low-impedance fuel injectors common on racing engines; programmable inputs to support cooling fan control; 64 channel internal data logging, and more. Real-time programming software helps dial in combinations very quickly. There are several PNs of the Gen 8 for different applications; the one compatible with LS engines carries PN 75807.
Another popular standalone engine controller is F.A.S.T.’s XFI system. Like the ACCEL/DFI Gen 8 controller, it handles high-performance, lowimpedance injectors and enables the use of up to 16 injectors (a trait factory controllers don’t have). Another benefit is the XFI system’s ability to store four separate engine mapping programs (tune ups), allowing the user to switch fuels (pump gas to racing gas or E85, for example) without having to re-flash the memory. The different tunes can be accessed with the simple flip of a switch.
Alameddine further suggests a computer swap in a force-inducted setup with a high-performance camshaft.
“The stock racing-oriented computer cannot compensate for a high level of valve overlap, causing coldstartup issues and general poor-idle quality—and mass airflow sensors typically have a glass ceiling for measurement of airflow, limiting potential power levels,” he says. “While there are many flash programs available to compensate at some level, usually the end user fights some degree of performance to dial in the whole package.”
Along with the products from ACCEL/DFI, standalone control systems are also available in the forms of F.A.S.T.’s XFI electronic fuelinjection system and Big Stuff 3’s GEN3 Pro SEFI control system.
Chassis Dyno Tuning
Whether a modified vehicle uses a pre-programmed software program or a custom tune, it is highly recommended that the vehicle be tested and fine tuned with the assistance of a chassis dynamometer. It more closely replicates the real-world performance of the engine by putting a load on the drivetrain. Of course, it also indicates the horsepower and torque levels of the engine. Those numbers are generally referred to as “at the wheels” power numbers, because they’re measured at the drive wheels on the dynamometer’s inertia drums (the large rollers on which the vehicle is loaded).
Depending on the type of dyno used, the at-the-wheels power numbers can be corrected by a factor of about 15 to 20 percent to indicate the true horsepower and torque output of the engine. The difference between the engine and drive wheels is the result of parasitic losses from the engine turning the transmission, driveshaft, rear axle, etc., before the horsepower and torque get to the pavement.
Most tuning shops use chassis dynos from either Mustang Dynamometer or Dynojet. Generally, the same car tested under the same conditions reveals slightly more at-the-wheels power on a Dynojet dynamometer than a Mustang dyno, although many tuners suggest the Mustang unit imposes a more real-world load on the vehicle that produces a result closer to what the vehicle will deliver on the street.
A chassis dynamometer is a wonderful tool for gauging before-and-after results of a supercharger or turbocharger, as well as ensuring the air/fuel ratio is adequate at WOT. Generally speaking, automatic transmission-equipped vehicles lose more of the engine’s power before reaching the drive wheels. Testing automatic-transmission-equipped vehicles can be difficult on a chassis dyno, because their factory lockup-style converters don’t always lock up. That means full engine power isn’t being transmitted to the drive axle. However, a knowledgeable dyno operator can get the converter to lock and take an accurate measurement. All-wheel-drive vehicles (like the TrailBlazer SS) also pose a unique challenge. They require a dyno with both front and rear rolling drums, which can be difficult to find, even in metropolitan areas with numerous tuning shops.
After a “pull” on the chassis dyno, the technician notes the recorded horsepower and torque measurements at the rear wheels and compares them with the baseline numbers that were recorded prior to the installation of the supercharger or turbo system. The graphs generated by the dyno pull not only point out the peak power numbers, but graph them in RPM increments, showing where in the rev range the power increases are most effective. If the vehicle is equipped with wideband oxygen sensors, air/fuel ratio measurements are also compared.
Part-throttle performance is more accurately tested on the road, with air/fuel ratio measurements recorded through a wideband oxygen sensor. Wideband sensors are also used on the chassis dyno during WOT tests, but they are acutely effective at helping fine-tune low-speed drivability and ensuring adequate fuel is available at all RPM and throttle levels.
Confirmation of a newly modified vehicle’s power output is certainly important, but ensuring adequate fuel delivery under load is the most important aspect of dyno tuning. It is imperative to know that the engine is free from detonation at WOT and under full boost. For vehicles undergoing a custom tune, such testing helps determine the precise fuel requirements throughout the RPM range.
Frankly, some tuners are better than others—and a professional shop that’s adept at installing parts and fabricating custom systems may not have a staff member who is experienced at the finer points of tuning electronically controlled engines. It is incumbent on the vehicle owner to seek the most qualified tuner to ensure a costly investment in a blower or turbo kit isn’t going to end prematurely with burned pistons. The Internet makes it relatively easy to probe whether a tuning shop has a good reputation, while old-fashioned asking around at the drag strip or a car show may also help find a knowledgeable local tuner.
Wideband Tuning
As helpful as chassis dyno tuning is, the measurements on the dyno are generated with the engine at WOT. Ensuring a safe air/fuel ratio and adequate fuel delivery at full throttle is, of course, vitally important, but part-throttle driving makes up the vast majority of conditions for street-driven vehicles. Tuning for those conditions ensures not only the appropriate air/fuel ratio across the RPM band, but optimizes idle quality, overall drivability, and even fuel economy.
The most accurate way to account for “real world” driving conditions is through what is known as wideband tuning, which requires a wideband oxygen sensor and supporting components. By replacing the original narrowband oxygen sensor with the wideband one, a greater range of air/fuel ratio detection is enabled. The value of the variation from the ideal, stoichiometric 14.7:1 ratio (when using gasoline) is expressed with the Greek letter Lambda (λ).
With the factory-style narrowband oxygen sensor, its capability is basically limited to determining whether the post-combustion air/ fuel ratio is at the optimal 14.7:1. If not, it triggers the “Check Engine” light and registers a code in the computer. A diagnostic check reveals if the difference was because of a rich condition (more fuel than air) or a potentially engine-damaging lean condition (more air than fuel).
A wideband oxygen sensor simply replaces the standard narrowband sensor in the exhaust system. One should be used in each position originally occupied by a narrowband sensor; most range in price from $50 to $100 each. If you plan to tune the engine yourself, it is a worthy investment. If you use a professional shop for tuning, the shop can usually swap out the standard sensors for wideband sensors during tuning sessions.
These graphs illustrate the difference in air/fuel measurements recorded by narrowband (left) and wideband (right) sensors. In the narrowband graph, the measurement within the 1.0 value section depicts the limited sensing range of the sensor, whereas the wider sensing range with the wideband sensor is clear. More importantly for tuners, the wideband sensor tells how lean or rich the mixture is, while the narrowband sensor merely indicates a rich or lean condition.
Unfortunately for tuners of modified vehicles—especially those with supercharged or turbocharged engines—the narrowband sensor signals rich or lean, but cannot indicate the precise air/fuel ratio that triggered the code. A wideband system has the capability of precise measurements. Typically, a wideband oxygen sensor identifies air/fuel ratios between 9.65:1 and 20:1.
Because incorrectly tuned forcedinduction systems can quickly lean out the air/fuel ratio, wideband tuning should be considered a must. In fact, for engine safety’s sake, many tuners build in a slightly rich ratio to ensure adequate fuel for any operating or engine-load condition. Typically, such tuning scrubs off a few horsepower, but the tradeoff is often welcomed because it brings with it peace of mind. Without wideband tuning, it would be difficult to accurately measure the air/fuel ratio and optimize it to ensure a safe tune that doesn’t drastically affect the engine’s output.
Electronic Throttle
Some builders have discovered a problem with the electronically controlled throttle body of some LS engines, particularly LS2 engines found in TrailBlazer SS and SSR models. The issue involves the throttle blade being pushed open unintentionally by the supercharger/ turbocharger boost pressure.
The condition is usually detected through uneven performance, bucking, and even an illuminated “Check Engine” warning. It is believed the culprit is a comparatively weak spring within the throttle body and the cure is the installation of another production throttle body with a stronger spring mechanism. Builders who’ve dealt with this issue report the 2005–2007 Corvette LS2 engine’s throttle body has sufficient spring strength to stand up to considerable boost pressure. Another possible culprit may be an insufficiently strong bypass valve.
Most Gen IV LS engines use electronically controlled throttles, but they’re not all manufactured with the same internal components. A strong throttle spring is necessary to prevent boost creep that affects tuning and could possibly harm the engine. Higher-boost supercharged and turbocharged engines must all have adequate bypass valves and/or blow-off valves or waste gates.
Also required for a methanol injection system is a pump to deliver the solution to the intake system. Unfortunately, the pump for the windshield-washer system that pairs with the reservoir isn’t strong enough to generate the pressure necessary to provide a finely atomized spray of the alcohol solution in the intake tract. This example is from methanol injection specialist Snow Performance.
A homemade methanol injection system is relatively easy to build. A salvage-yard windshield-washer reservoir makes a perfect storage tank for the methanol solution. Filling up with windshield-washer solution is cheaper and easier than tuning the engine to run on high-octane racing gas, too.
Another throttle-related issue seems to affect the TrailBlazer SS, Hummer H3, and other all-wheel-drive vehicles. The comparatively violent acceleration caused by a full-throttle blast with a force-inducted engine can upset the factory stability-control system called StabiliTrak. When this occurs, a warning message may flash on the dashboard and temporarily disable the stability system. It may also cause the stability system to perform in a manner where it believes it is intervening in a potentially hazardous driving situation. If that happens, the spark may be retarded and the throttle position reduced—even under boost— because that’s what the stability system is programmed to do.
Lingenfelter Performance Engineering has a simple module that “tricks” the stability system with a more appropriate torque signal and it works for most—but not all— LS-powered all-wheel-drive vehicles. It’s called the Delivered Torque Output Limiter (DTOL) and its PN is L460021105.
Methanol Injection
Pushing the edge of the envelope with boosted performance has inherent risks in engine combinations using stock rotating assemblies, not the least of which is detonation. Even with the necessary air-to-air or air-to-liquid intercooling systems, the boundaries of sustainable, pumpgas performance can be easily reached with only moderate boost levels. One of the ways some tuners expand the pump-gas safe range is with a methanol injection system.
In a nutshell, an alcohol-based solution—usually a 50/50 mix of methanol and water or even blue windshield-washer solution—is injected with the regular fuel supply and delivers a pair of significant advantages: lower inlet temperatures and a greater effective octane rating. Essentially, methanol injection acts as a secondary intercooler. Injection of the solution is done in the intake stream, ahead of the throttle body, much like the nozzle does for a dry nitrous system.
The intake tract is drilled to accept a nozzle for the methanol injection system, just as it would be for a bolton nitrous system. Fortunately, no fuel-system modifications are required for methanol injection, but tuning is necessary to optimize its advantages.
Of course, a methanol-injection system must be accounted for in the tuning, but the lower inlet temperature and higher octane rating enable more aggressive programming. Snow Performance is the aftermarket industry authority on methanolinjection systems. It offers installation kits, as well as a pre-mixed methanol solution.
The user must closely gauge the range of the alcohol solution to ensure it matches the gas tank. In other words, if the methanol tank runs dry before the gas tank, a larger methanol tank is needed. In very general terms, a gallon of methanol/water solution should last roughly the range of an average fuel tank. Of course, larger vehicles, such as the G8/Commodore and trucks have larger gas tanks.
The Martin SS 427 Package
It delivers more than 725 supercharged horsepower from 427 ci and does so with the docile driving manners of a family sedan. That’s the Martin SS 427—a package for the fifth generation Camaro from longtime Pro Mod drag racer and racing-shop proprietor Harold Martin.
More than a bolt-on blower kit, the SS 427 package is based on a larger-displacement version of the standard LS3 engine, which grows from 376 to 427 ci through greater bore-and-stroke dimensions. Along with that is a set of modified LS3 cylinder heads and a ProCharger D-1SC centrifugal supercharger and intercooler system that generates around 11 pounds of boost. Martin’s claimed rating for the engine is 727 hp and 700 ft-lbs of torque.
The impressive Martin SS 427 Camaro, with 727 hp and 700 ft-lbs of torque, gets its ample power from a 7.0-liter engine based on the car’s original 6.2-liter LS3.
A ProCharger D-1SC blower and intercooler are used on the Martin SS 427, generating about 11 pounds of boost at the throttle body. A smaller pulley is used on the blower to generate more boost for the larger-displacement engine. The factory E38 controller is used with this engine combination and enables excellent drivability.
Importantly, the completely modified engine uses the stock E38 controller that was carefully tuned for the combination. The engine starts, idles, and pulls through the rev range without stalling, hiccupping, stumbling, or any other tuning issues. It’s a daily-drivable, 727-hp street car.
Written by Barry Kluczyk and Posted with Permission of CarTechBooks
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