1SloLQ9

Hey guys, I'm buying a 2005 avalanche 2500, I've noticed on the hypertech site that the 02 and previous engines made more power on the dyno before and after hypertech, The 03 and up made less power with and without tunes, Is this something to do with programming? or are the cams or engines different? the 02 made 291whp at 4250 and the 03+ made 283whp. Not staggering, But.. I've read postings of guys who have owned an 02 and an 03 and said the 02 was noticeably more powerful. Any insight would be great!!

Thanks

Raylar Engineering

Pretty sure everything is the same from one year to the next. They could have tested things on different dynos, or with different transmissions (Allison vs 4L80e), or a million other variables.

The power programmers are a solution if you plan to keep the vehicle totally stock. Otherwise, I suggest you take a look at our site. Your 496 could be making over 600 horsepower naturally aspirated.

1SloLQ9

Yeah I would probably have my buddy tune it if anything, He tunes with efi live and does an excellent job. He was actually on the duramax forums a few years back with results of dyno tuning an 8.1 with e85 before it became real popular. I was over on the chevy avalanche forum and one of the guys on there said the 02 and 01 had different mufflers, due to sound and emissions i'm sure. So maybe the newer one's restricted flow.

Since you are the king of these 8.1's and aftermarket solutions, Have you ever had anyone do an H pipe configuration right after the manifolds some how? Just to get the scavenging effect as close to the motor as possible?

I'm thinking of a way to do this and see if there is any gain, Assuming it would mostly effect low end torque.

whippled 8.1l build

just go FI and be happy with 700hp at low boost

hog

Ask, and ye shall recieve. This is on eof my posts from another forum

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxx
Ive compiled the improvements to the GEN V11(GEN7) BBC Chev has made over the years from online GM literature.
.
2001
Vortec 8100 Big Block V8 Outpowers Competitor’s V10s

The Vortec 8100 (L18) is essentially a new engine. Nearly 80 percent of its parts have been redesigned. Yet, its foundation is one of the most celebrated engine components in automotive history, GM’s Big Block V8. The Big Block even competes against diesels in highly demanding marine and industrial applications – in essence giving Silverado and Sierra HD customers a lot more truck engine for the money than they realize.

The new Vortec 8100 shares its predecessor Vortec 7400’s valve and bore centers and bore diameter. But its stroke has been increased by 9.4 mm (.37 in.) for a higher displacement and more power. The result is awesome: the Vortec 8100 out-muscles even Ford and Dodge’s V10s!


Horsepower Torque
Manufacturer – Engine
--------------------------------------------------------------------------------
GM – Vortec 8100 V8 gas
340hp @ 4200 rpm
455 lb/ft @ 3200 rpm
--------------------------------------------------------------------------------
Ford – 6.8L V10 gas
275 hp @ 4250 rpm
410 lb/ft @ 2650 epm
--------------------------------------------------------------------------------
Dodge – 8.0L V10 gas
300 hp @ 4000 rpm
425 lb/ft @ 2800 rpm
--------------------------------------------------------------------------------
If there is heavy towing or hauling to be done, this is the perfect powerhouse for the job. An impressive 90 percent of its peak torque is available from 1700 rpm to 4300 rpm. And when it comes to acceleration, this engine leaves its competitors in the dust, as the following comparison of comparably loaded, automatic transmission-equipped models shows.
1) 0-60(sec.)

2) 30-70 (sec.)

3) 1/4 mile (sec.)

4) Speed (mph) in 1/4 mile

At 11,400-lb. GVW load level

Vortec 8100 with 4.10 axle ratio
1) 13.4
2) 13.8
3) 19.7
4) 74.0
--------------------------------------------------------------------------------
Ford 6.8L with 4.30 axle ratio
1) 15.7
2) 16.8
3) 20.8
4) 69.3
--------------------------------------------------------------------------------
Dodge 8.0L with 4.10 axle ratio
1) 16.3
2) 16.7
3) 21.1
4) 68.1
--------------------------------------------------------------------------------

At 22,000-lb GCW load level

Vortec 8100 with 4.10 axle ratio
1) 25.8
2) 26.2
3) 25.0
4) 59.1
--------------------------------------------------------------------------------
Ford 6.8L with 4.30 axle ratio
1) 32.3
2) 36.0
3) 27.0
4) 53.9
--------------------------------------------------------------------------------
Dodge 8.0L with 4.10 axle ratio
1) 32.2
2) 34.2
3) 27.0
4) 54.5
--------------------------------------------------------------------------------
Even with the Vortec 8100’s awesome power and performance, its specific fuel economy (per liter of displacement) is four percent better (than the 6.5 liter).

And the Vortec 8100 operates more cleanly; it already complies with 2002 "clean-fuel-fleet" requirements. Its new design also permits running on alternative fuels, including liquid propane gas (LPG) or compressed natural gas (CNG), without requiring any special valves and seats. California versions of the engine are equipped with Air Injection Reaction (AIR) and pup catalytic converters to meet that state’s more stringent emissions requirements.

The Vortec 8100’s 200,000-mile (322,000-km) durability testing includes rigors that no other gasoline engine in its class have been put through; they include running at wide-open throttle for 300 straight hours!

Its low maintenance design requires only normal oil and filter changes during the first 100,000 miles (160,000 kms). Oil changes are based on actual need. The Powertrain Control Module records engine temperature and length of operation at a given temperature, then indicates the need for an oil change with an easy-to-read "Change Engine Oil" LCD message in the Driver Message Center. The driver is also alerted to "Check Engine Oil Level," when necessary.

Long-life engine coolant is good for five years or 150,000 miles (240,000 kms). A standard coolant level sensor warns the driver of a drop in coolant level. If a catastrophic event causes a total coolant loss, the engine protects itself against damage by running on alternate banks of four cylinders and using cool air to cool itself, enabling the driver to reach a service station.

Advanced Design Features
The Vortec 8100’s rigid cylinder block uses four-bolt main bearings to optimize crankshaft rigidity. The nodular iron crank is internally balanced and counterweighted to minimize internal stresses and bearing loads. The bearings are produced with a new alloy (A260) that increases their life and eliminates the use of environmentally hazardous cadmium. An elastic material called Vamac is used in place of rubber to support the crankshaft’s torsional rigidity: it increases both damping capability and durability. A change in the firing order (to 1-8-7-2-6-5-4-3) reduces main bearing wear and stress on the crank by seven percent.
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxx

Hope that helps

peace
Hog

hog

A coil-near-plug ignition system increases ignition energy by 50 percent, reduces emissions and improves idle quality.

New pistons have a shorter deck height and skirt length; they permit the longer (0.37 inch/9.4 mm) engine stroke, without any significant increase in engine deck height and minimal heat build-up. A Teflon™ coating reduces friction. An especially short (5 mm) top ring land and new full-radius top ring design improve combustion efficiency and reduce exhaust emissions.

New cylinder heads feature replicated intake ports (each precisely equal in diameter and length) for improved fuel-air distribution and a reduction cylinder-to-cylinder variations in torque output, improving operating smoothness and efficiency. Powdered-metal exhaust valve seats and cast-iron guides enhance durability. Five head bolts circle each cylinder to assure reliable lifetime sealing, which is further enhanced by (1.3 mm) thicker, more durable head gaskets.

Hydraulic roller lifters ride on a durable steel camshaft. Stiffer ball-pivot studs support more robust rocker arms. A cast-iron cam-drive cover adds to the valvetrain’s quiet operation.

The aluminum intake manifold’s long, even-length runners yield a broad, flat torque curve plus excellent volumetric efficiency (breathing) at high rpm. The manifold is more precisely made, using a "lost foam" casting technology. It involves making a styrofoam assembly; pouring sand around it and shaking the sand into voids. Molten aluminum is then poured through the sand. It melts that foam, displaces it and cools in the shape of the part. The process permits more intricate internal crankcase ventilation passages that eliminate the need for an external crankcase valve and plumbing. This cuts maintenance costs and eliminates potential leak sources.

Fuel is delivered by a high-pressure (400 kPa) sequential port fuel injection, providing quick starts and smooth operation in cold and hot weather. An Electronic Throttle Control (ETC) meters intake air more precisely. It also reduces weight and enhances reliability/durability by replacing the 7.4 liter’s mechanical hardware with electronic sensors, wires and actuators and integrating functions such as cruise control, brake torque management and traction control into a single controller. The Vortec 8100’s new mass airflow sensor also has an integral temperature sensor to facilitate fine mixture adjustments.

Stainless steel exhaust manifolds (replacing the Vortec 7400’s cast iron) are significantly more heat resistant and durable. Manifold shields keep heat out of the engine bay and muffle the sound of high velocity exhaust flow.

The improved (over the Vortec 7400) cooling system is fully pressurized, it includes a surge tank and a single, aluminum-body double-volute pump. The pump has a durable, cast-iron case, and longer-life silicon-carbide shaft seal. Its redesigned water jackets provide more flow, and it distributes equal amounts to both banks of the cylinder case for greater efficiency. A 100 mm wider radiator provides two more liters of capacity. The transmission cooler has been relocated to boost airflow. A modulating fan clutch provides quieter operation. To prevent any potential leaks, fitting beads and hose ends were designed for tighter, more reliable fit; clamps are specified for optimum pressure and glued in place on hoses to assure proper alignment and secure sealing.

A dual belt accessory drive de-couples the engine’s alternator and accessories from the air conditioning compressor. This reduces loads on the accessory pulleys by up to 50 percent (over the Vortec 7400), improving efficiency and belt life. It also reduces accessory drive noise by nearly 50 percent (7 dBA) at 1000 rpm and further increases interior comfort by permitting the A.C. compressor to be located as far as possible from the passenger compartment. Stiff cast-iron accessory mounting brackets also help reduced noise and vibration. The drive belts are constructed of a new, non-neoprene compound that extends their life to 150,000 miles (240,000 km).

Controlled compression gaskets are used in the oil pan, rocker covers and intake manifold to eliminate leaks. Rocker rails have also been raised to prevent oil from puddling against the rocker cover gaskets.

A three-piece, thermoplastic sight shield adds to the advanced look of this superlative engine.




2002
Silverado provides the most powerful line of three-quarter and one-ton pickups and chassis cabs in the heavy-duty pickup segment
Silverado HD dominates competitors in engine power, payload and pulling



2003
CHEVROLET EXPRESS AND GMC SAVANA APPLICATION ELIMINATED
The Vortec 8100 is no longer an option in the Express and Savana. The Vortec 6000 6.0L (LQ4) will be the most powerful engine offered in the redesigned 2003 models (see Product Specifications).

POWERTRAIN CONTROL MODULE AND SOFTWARE WITH ADDITIONAL MONITORING FUNCTIONS
A new Powertrain Control Module (PCM), called P59, manages the 8.1L. With this new PCM, processor clock speed increases from 21 to 24 mHz and memory capacity doubles to 1.1 megabytes. The PCM also manages the 4.3L V6 (LU3) and all gasoline-powered Vortec V8 truck engines, and provides one of the most sophisticated engine control systems in the industry.

Commonality offers the advantage of reducing inventory complexity and increasing efficiency at various assembly plants. More important, P59 offers the most precise engine management possible, optimizing performance according to temperature or operating conditions and virtually eliminating unintended variation in every function it controls, from ignition timing to fuel delivery to transmission shift points. It also allows GM Powertrain engineers to monitor more engine operations and improves the accuracy and robustness of the OBDII (On-Board Diagnostics) system.

For example, the PCM now measures electrical current flowing to the oxygen or 02 sensors (crucial components of the emissions-control system) on vehicles equipped with the Vortec 8100. Previously, the O2 sensors were monitored with a time-to-activity algorithm, which required more measurement latitude to ensure proper operation. The new PCM more quickly reports a malfunction in an O2 sensor with virtually no margin for misreporting. It also allows a new Engine Off Natural Vacuum (EONV) diagnostic for the Onboard Refueling Vapor Recovery system (ORVR), which reduces evaporative emissions by preventing gasoline vapor from escaping the vehicle into the atmosphere. With EONV, the PCM continues to operate when the engine is turned off, monitoring pressure in the fuel tank and ORVR system. If pressure bleeds off more quickly than ambient temperature and other conditions indicate, the PCM can determine whether the system has a leak, even when the vehicle is parked. The new PCM ensures that the engine operates according government emissions regulations. And thanks to its precision, it will also reduce the number of false alarms— OBDII “service engine” warning lights—that require dealer intervention.

hog

The new PCM is roughly the same size as the PCM it replaces and is installed in the same place as the previous PCM in various applications—in all applications on the firewall or inner fender, depending on the vehicle. There is no visible difference in the engine bay.

IMPROVED DENSO OXYGEN (O2) SENSORS
The Vortec 8100 has new oxygen (O2) sensors. These O2 sensors have the same 6.6-volt heat rating as the parts they replace, allowing them to achieve closed loop operation—and maximum exhaust emissions reduction--in minimum time. The new sensors allowed engineers to implement the current monitoring function provided by the new PCM, and they are common to other truck gasoline V8s.

SOLID STATE OIL-PRESSURE SENSOR
The 8.1L now has a fully electronic, solid-state oil pressure sensor, replacing an analog/mechanical sensor. The solid-state sensor is installed in the same location in the engine block, but it has no mechanical parts, increasing reliability. Its introduction coincides with a new electronic instrument package in some applications.

REVISED ELECTRONIC THROTTLE BODY
The Electronic Throttle Control (ETC) system on the 8.1L uses a new throttle body and Throttle Actuator Control (TAC) module. The throttle body’s diameter (75 millimeter) has not changed, but the new part features a ``wrap around’’ throttle motor. The electric motor that operates the throttle plate is literally built around the throttle body and responds more quickly to commands from the TAC. The new throttle body is now common to all gasoline-powered GM truck V8s.

Before the Vortec 8100, ETC was largely reserved for premium passenger car engines and some heavy duty trucks. There is no mechanical link between the accelerator pedal and the throttle. Besides throttle pedal angle, the PCM measures other data, including the transmission's shift points, in determining how far to open the throttle. ETC delivers outstanding throttle response and can be calibrated to match demands in different applications.

COOLANT FLOW FROM HEATER CORE REVISED ON SILVERADO AND SIERRA
In the 8.1L applications, the flow pattern for engine coolant has been revised to heat the cab more quickly during cold temperature operation.

The heater core is a small radiator inside the vehicle’s instrument panel, behind the engine firewall. Hot coolant from the engine flows through the heater core, where the ventilation fan forces heat through ductwork to the dash vents and into the cab. In extremely cold temperatures, large displacement engines such as the 8.1L can take some time to reach a temperature sufficient to heat the cab. GM engineers have developed a simple, effective method to increase customer comfort by shortening the time it takes to heat the cab.

On Silverados and Sierras, the heater return hose is now routed into the radiator return hose rather than the radiator itself. That means the coolant flowing in and out of the heater core bypasses the radiator, where coolant is at its coldest temperature anywhere in the cooling system. Coolant flowing to the heater core stays out of the radiator until the engine reaches full operating temperature and the thermostat opens. This allows the cab to heat more quickly, meeting GM’s stringent time standard, without reducing cooling capacity during high-temperature operation.

2004
LOW PERMEABILITY INTAKE MANIFOLD AND THROTTLE BODY GASKETS
The Vortec 8100 has new intake manifold sealing gaskets manufactured from a fluorocarbon material. These fluorocarbon gaskets represent the best sealing technology available. The gaskets are resistant to most chemicals, for maximum durability, and particularly impermeable to small hydrocarbon molecules. Gasoline vapor cannot penetrate the fluorocarbon. Moreover, the gaskets are designed to improve sealing for the life of the engine. They are molded with slight protrusions, or ``snouts,’’ that fit into counter-bores milled in the cylinder heads. The snouts more positively locate the gaskets and virtually eliminate the possibility of movement during assembly or after repeated thermal cycling over the life of the engine.

IMPROVED ONBOARD REFUELING VAPOR RECOVERY (ORVR) SYSTEM FOR CHEVROLET AVALANCHE AND SILVERADO, GMC SIERRA AND YUKON XL
The ORVR system on these Vortec 8100-equipped vehicles uses a new evaporative emissions canister and purge-control solenoid. ORVR reduces evaporative emissions by preventing gasoline vapor from escaping into the atmosphere during refueling. These new ORVR components take full advantage of advanced technology built into the Vortec 8100's P59 Powertrain Control Module (PCM). The PCM and new components more efficiently manage ORVR, and improve the accuracy and robustness of the OBDII (On-Board Diagnostics) system. This precision will reduce the number of false alarms – OBDII ``service engine’’ warning lights – that require dealer intervention.

With improvements to ORVR, the returnless fuel injection and low-permeability gaskets, the Vortec 8100 meets new, near-zero evaporative emissions standards mandated for 2004.

EXHAUST GAS RECIRCULATION (EGR) ELIMINATED
The EGR control valve and plumbing have been removed from all Vortec 8100s. The EGR system was used to recycle some exhaust gas back into the intake stream to cool combustion and reduce oxides of nitrogen (NOx) emissions. Data from development and durability test vehicles indicates that software refinements in the P59 PCM, and the engine’s overall efficiency, allow the Vortec 8100 to meet all 2004 North American exhaust emissions standards without EGR. Removing EGR reduces cost, complexity and potential warranty claims, improving both assembly efficiency and reliability.

IMPROVED CRANK AND CAM TIMING SENSORS
Vortec 8100s are equipped with new crankshaft and camshaft timing sensors. The sensors continue to operate on the Magnetic Reluctance (MR) or “mirror image” ignition timing principle, ensuring precise measurement over the life of the engine without adjustment. These sensors are now common with those used on other Vortec V-8s, helping streamline purchasing requirements, reducing inventory requirements and increasing efficiency at engine assembly plants.

IMPROVED CRANKSHAFT SEAL
The Vortec 8100 has a new front engine cover with a redesigned crankshaft seal. The seal requires no particular orientation during installation. It reduces engine assembly time and virtually eliminates the possibility of misalignment.

ADJUSTABLE THROTTLE PEDAL FOR WORKHORSE CUSTOM CHASSIS
WCC commercial vehicles will be offered with a throttle pedal that can be moved to accommodate different drivers. Vortec 8100s built for this application require PCM software recalibration to manage the electronic throttle control. There are no hardware changes.

REVISED CYLINDER HEADS FOR INDUSTRIAL APPLICATIONS
Vortec 8100s built for industrial use have new valve and valve seat material and new springs. Industrial engines typically operate at relatively low, steady rpm (1800-2000), creating different demands than the typical truck duty cycle. The valve seats in industrial Vortec 8100s have been metallurgically improved with induction hardening, and valve-spring tension has been reduced to soften valve interaction with the seats during low speed operation. Finally, industrial engines are now equipped with the same Silcrome 1 valves used in Vortec 8100s built for trucks. This material includes tungsten, vanadium, manganese and silicone, with higher chromium content than conventional iron valve alloy. The Silicrome 1 valves ensure long-term durability in industrial engines and increase efficiency at the engine plant by reducing inventory.

hog

2005
FLOATING PIN PISTONS
The Vortec 8100 is fitted with new floating-pin pistons. Introduced previously on GM Powertrain’s Vortec 6000 V-8, these pistons feature wrist pins that “float” inside the rod bushing and the pin bores in the piston barrel. Previously, the Vortec 8100 used a fixed-pin assembly, in which the connecting rod is fixed to the piston’s wrist pin, and the pin rotates in the pin bore. In the Vortec 8100, snap rings now retain the wrist pin in the piston, while the rod moves laterally on a bushing around the pin.

The Vortec 8100’s pistons, piston rings and connecting rods are identical to those used in 2004. The new floating-pin assembly allows tighter pin to pin-bore tolerances and reduces noise generated during engine operation.

RETURNLESS FUEL INJECTION FOR MARINE APPLICATIONS
All Vortec 8100s built for marine application are equipped with a new ``returnless’’ fuel injection system that eliminates fuel return lines between the engine and the gasoline tank. The new fuel system is also known as a demand system, and was introduced on Vortec 8100s built for the Chevrolet Silverado and GMC Sierra for model year 2004.

Before model year 2004, the sequential fuel injection (SFI) on all Vortec 8100s used a return line to manage fuel pressure by bleeding off excess fuel at the fuel rail and returning the excess to the tank. The new system eliminates the return lines and moves the fuel pressure regulator from the fuel rail on the engine to the fuel tank. The fuel line from the tank now includes pulse dampeners, or a series of baffles, that manage fuel pulsing and limit noise.

Because it delivers only the amount of fuel need by the injectors, and returns no fuel to the gas tank, the returnless system essentially eliminates heat transfer from the engine to tank. This reduces the amount of vapor generated in the tank and released as evaporation. The returnless system has been introduced on marine engines to give marine customers the same emissions standards and efficient operation as truck customers.

IMPROVED OIL PAN FOR MEDIUM DUTY AND MARINE APPLICATIONS
The oil pan on Vortec 8100s built for medium-duty (C4-C8 trucks) and marine use has been redesigned. This cast aluminum oil pan is essentially identical for both applications, with differences limited to final machining.

With the new pan, the interior baffle has been reconfigured to maximize oil flow, improve durability and stiffen the cast-aluminum pan’s structure, further reducing engine vibration. Moreover, sump capacity for medium-duty trucks increases 3.1 liters. The change was driven by the demands of the commercial fleet and rental markets. Rental truck customers may not be the most diligent operators when it comes to monitoring oil levels. The larger sump adds an extra measure of security for rental companies and fleet operators, even if customers use trucks for weeks without checking oil levels.

IMPROVED THROTTLE ACTUATOR CONTROL MODULE
All Vortec 8100’s are equipped with an improved throttle actuator control (TAC) module. Located on the throttle body, the TAC module is an integral component of the Vortec 8100’s electronic throttle control (ETC) system. The TAC takes command from the powertrain control module (PCM) and then operates the motor that opens and closes the throttle plate.

The TAC module has new read-only memory and control software. Like its predecessor, it allows multiple throttle progressions or algorithms, which operate the throttle at varying rates according to operating conditions and driver demands. It also has built-in default settings that protect the engine and ensure safe operation in the event of malfunction with the ETC or other engine subsystems.

RATE-BASED DIAGNOSTICS
The Vortec 8100’s powertrain control module (PCM) uses a new monitoring protocol known as rate-based diagnostics. Rate-based diagnostics improve the robustness of the Onboard Diagnostics System (OBD II) and ensure optimal performance of emissions control systems.

With rate-based diagnostics, the PCM applies a new formula to manage OBD II. Essentially, new software increases the frequency at which the PCM checks various engine systems, and particularly emissions-control systems such as the catalytic converter, oxygen sensors and exhaust gas recirculation (EGR). Rate-based diagnostics more reliably monitor real-word operation of these systems, and allow regulatory agencies to more easily measure and certify emissions compliance. The new protocol allows the Vortec 8100 to meet more stringent OBD II requirements two years ahead of a mandate by the California Air Resources Board.

GF-4 ENGINE OIL
All Vortec 8100s will be shipped to customers with a new engine oil that reduces engine deposits, extends oil change intervals, improves fuel economy and extends the life of emissions control systems. GM Powertrain has taken a leading role in developing and introducing the new oil, designated GF-4 (for “Gasoline Fueled, Standard 4’’) by the American Petroleum Institute.

GF-4 contains a new ash-free antioxidant ingredient and less phosphorous than the previous formulation (GF-3). The typical automotive engine now operates at a much higher temperature than an engine built 10 years ago. GF-4 is twice as resistant to oxidizing, which can present itself as foaming, at high operating temperatures. At the same time, GF-4 provides better low-temperature protection, reducing engine wear during the critical cold-start period. Lower phosphorus and sulfur content – chemicals that are harmful to catalytic converters – will extend anticipated catalyst life beyond 120,000 miles. Finally, GF-4 lowers friction overall and retains its optimal friction-reducing characteristics longer. The result is an anticipated improvement of 0.2 percent to 0.3 percent in an engine’s fuel economy, and longer oil change intervals.

Production of Vortec 8100s with GF-4 begin in fall 2004, ahead of an industry recommendation of April 30, 2005. This will allow vehicles with the Vortec 8100 to be tested for 2005 Corporate Average Fuel Economy (CAFE) standards with GF-4. GM’s industry-leading Oil Life System may be adjusted to account for the new oil. The owner’s manual in vehicles equipped with the Vortec 8100 will continue to recommend oil with the Starburst logo, which must be certified to GF-4 by May 2005.

hog

2006
New dual mid-coupled catalytic converter system
Chevrolet Suburban, Avalanche and GMC Yukon XL three-quarter-ton models equipped with the Vortec 8100 receive a new M120 mid-coupled catalytic converter system. Two new mid-coupled converters replace four previous ones (two mid-coupled and two under-floor converters). The new dual converters, with about two liters of volume, are also located closer to the exhaust manifold to enhance their effectiveness. Their construction, consisting of multiple materials, is unchanged. While providing lower LEV emissions levels, the new converter system also allows a more moderate 47.1 kPa of exhaust back pressure for more power. Induction restriction is unchanged.
Improved electronic throttle control and throttle actuator control module
With the Vortec 8100, the Chevrolet Suburban, Avalanche and GMC Yukon XL 2500 Series also receive an improved electronic throttle control pedal and improved throttle actuator control (TAC) module. The throttle pedal provides more consistent truck-to-truck pedal force and effort feel for vehicle operators. The TAC is designed to accommodate the new pedal.
Located on the engine side of the front of dash, the TAC module is an integral component of the Vortec 8100’s electronic throttle control (ETC) system. The TAC takes command from the powertrain control module (PCM) and then operates the motor that opens and closes the throttle plate.
Like its predecessor, the TAC module has read-only memory and control software. It allows multiple throttle progressions or algorithms, which operate the throttle at varying rates according to operating conditions and driver demands. It also has built-in default settings that protect the engine and ensure safe operation in the event of malfunction with the ETC or other engine subsystems.

Returnless fuel injection for Chevrolet Kodiak and GMC TopKick
For 2006, the Vortec 8100 available in Chevrolet Kodiak and GMC Topkick medium duty trucks is equipped with a new "returnless" fuel injection system that eliminates fuel return lines between the engine and the gasoline tank. The new fuel system is also known as a demand system. The system is already used with the Vortec 8100 on Chevrolet Silverado and GMC Sierra models and with all Vortec 8100s built for marine applications.
Before 2006, the Sequential Fuel Injection (SFI) in medium duty trucks equipped with the Vortec 8100 used a return line to manage fuel pressure by bleeding off excess fuel at the fuel rail and returning the excess to the fuel tank. The new system eliminates the return lines and moves the fuel-pressure regulator from the fuel rail on the engine to the fuel tank. But because the returnless system delivers only the amount of fuel needed by the injectors, and returns no fuel to the fuel tank, it eliminates heat transfer from the engine to the fuel tank. This reduces the amount of vapor generated in the tank and captured by the evaporative emissions control system.
Recalibrated P59 engine controller
The Vortec 8100’s P59 engine controller in medium duty trucks is recalibrated to coordinate with the newly available version of the Allison five-speed automatic transmission and the returnless fuel injection system. The P59 also has new calibrations to optimize driveability and fuel economy with the new Allison six-speed automatic transmission being introduced for the first time in GM full-size pickups.


2007
HEXAVALENT CHROME ELIMINATED
An ongoing process to eliminate heavy metals from engines results in one small component—the drain plug—being replaced by a hexavalent chrome-free part.

Overview
Few words generate excitement for car and truck enthusiasts like ‘’Big Block.’’ The Vortec 8.1L V8 is the legendary GM Big Block for a new millennium, with a longer expected useful life and horsepower and torque that surpass the large-displacement gasoline engines offered in competitors’ heavy-duty pickups. This heavy-duty engine also sets benchmarks for marine and industrial applications worldwide.

After extensive analysis of competitors' engines, the Vortec 8.1L development team set a goal of 200,000 miles of useful life without major repairs – and achieved it. Before it was ready for production, this big block had to pass the “Marine Dock'' test, in which it is run at full throttle for 300 consecutive hours without a failure, and a minimum of 1,000 hours at full-throttle operation for truck applications.

In the six years since its launch, virtually every aspect of the engine – from sealing to electronic management to noise, vibration and harshness control – has been re-examined and improved.

GM's leadership in big block V8 technology dates to at least 1958, when the Vortec 8.1L's progenitor was launched with 348 cubic inches of displacement in the full-size 1958 Chevrolets. The 348 was followed by several variants, including a 409, 366 and 427. In 1970, the 454-cubic-inch big-block was introduced. It was retooled in 1991 as the Vortec 7400 – a truly powerful pickup engine that met stringent 1990s emission requirements. The Vortec 8.1L bears little resemblance to those engines, but it maintains a tradition of outstanding durability and class-leading power.


2008
Carryover content and benefits from 2007 model year(no longer available in the new GMT900 2007.5+ trucks, only in commercial trucks)

2009
Carryover content and benefits from 2008 model year

2010
The GENVII , and the BBC in general is no more. The end of an era.
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxx

Hope that helps

peace
Hog

Raylar Engineering

An H-pipe downstream will balance the exhaust pulses between the two banks, but it won't do what you're looking for. The best way to increase power via scavenging is a set of long tube headers from Stainless Works. If you're limited by smog, 3/4 length headers like JBA's will work nicely as well.