Understanding the GENIII LS1/LS6 Control Systems and PCM

By:  Shawn Whitehead

aka: kewlbrz ( www.corvetteforum.com )

Website: www.vetteguru.com

Note: This is a work in progress and may change accordingly.  The obvious goal here is to assemble as much LS1/LS6 control system information as possible.  Any contributions will be noted and appreciated.


I want to pass along some information, in hopes that it will help those that are considering modding their C5 or LS1/LS6, and what happens when you do.
I don't claim to be an expert, and much of what I have learned, I have learned from; my own experiences, other enthusiasts, and elsewhere. There may be some errors below, but all of this information has been performed and researched over a long time by me, and is thought to be correct.


One of the most typical mod that most effects your system's calibration is modding the MAF. Adding cold-air systems, ported/polished throttle bodies, etc, serve to compound taking the system out of scope when used with a ported MAF.

This is a byproduct of enhancing the efficiency of the engine, and can be maximized if re-tuned properly.

Other modifications to the engine, including adding headers, all the way to heads/cam applications, and even full out, bored and stroked motors, all effect the system in much the same way a ported MAF does. Because when you increase the efficiency of the motor, you are changing the way it is calibrated to meter airflow, and fuel delivery.

I am attempting to be as low level as possible, yet also am trying to speak in layman terms where at all possible.

Some Acronyms
PCM - Powertrain Control Module (the cars brain)
MAF - Mass Air Flow Housing and Sensor
MAFT - MAF Translator (by Modern Musclecar)
GMS - Granetelli Motorsports MAF Housing
POT - Potentiometer (variable resistor)
WOT - Wide Open Throttle
Autotap - ODBII Diagnostic Tool
OBDII – On Board Diagnostics Version 2



Here is an internal view of the LS1 PCM that runs the whole show. This PCM is located in the engine bay on the passenger side behind the tire well on the C5.


Most GM enthusiast are familiar with the older Delco engine computers and the availability of so called 'hot chips', unfortunately with the GenIII PCM Delphi moved to using Flash ROM which did away with the need for a removable EPROM (Memcal). It's great if you have the tools to 'reflash' the memory in the PCM but unless you are a GM dealership such tools are probably a bit out of reach.

Looking at the picture, the MCU is clearly visible as the big square chip near the top, this MCU is based on the Motorola MC68332 but it seems to be a custom one for GM as there doesn't seem to be a 160pin 68332 in any Motorola docs. A few of it's features are a 32bit CPU and on board TPU (Time Processor Unit).

The MC68332 ia s highly-integrated 32 bit microcontroller that combines high-performance data manipulation capabilities with powerful peripheral subsystems.This MCU is built up from standard modules that interface through a common intermodule bus (IMB).

The MCU incorporates a 32 bit CPU (CPU32), a system integration module (SIM), a time processing unit (TPU), a queued serial module (QSM) and a 2 Kbyte static RAM module with TPU emulation capability (TPURAM).  The MCU can operate at 16, 20, and 25 MHz.

The MCU's System Integration Module Includes:

Motorola 68332 Tech Manual In Adobe PDF Format

To the right of the MCU is the Flash ROM, this is a 4 Mbit unit by Intel, this is where all the running code and calibrations are stored, it cannot be easily removed, but it can be reprogrammed (new calibrations etc) via the ALDL plug under the steering column with a Tech2 or similar device.

Down each side you can see many driver arrays mounted to a heatsink, these are all the drivers for various functions (Injectors, A/C relay, Fan Relays, Transmission Solenoids, Idle Stepper Motor, etc.). One smart move IMHO is that Delphi choose not to fire the 8 individual ignition coils directly from the PCM (unlike some other makes do), instead each cylinder has it's own 'igniter' mounted on it's coil and the PCM drives that with a low voltage pulse, the advantage there is that ignition coil failures happen, if they go short circuit then it usually takes out the igniter, if this is part of the PCM then you are up for another PCM instead of just 1 igniter and coil. Generally such a failure won't damage the PCM's internals if it does not directly fire the coils.

The PCM has the capability of running 8 Injectors sequentially, and firing 8 Individual Ignition coils as well as all the other O/P's that must be managed by the PCM. GM have always been great with their diagnostic info from computers, the GenIII PCM is no exception, with about 100+ different error codes it should be quite easy to pin point any errors that are detected.

MAF and Throttle Body Porting, and it's application

Obviously the reason people port their MAF, whether it's by physically porting it, adding MAF ends (97-00 only), or by replacing the entire unit, GMS etc..., it is to increase the engines ability to take in air, and also attempt to increase timing advance, by inducing less perceived load.

A stock 97-00 MAF is comprised of several components.

- the center housing and heated elements
- outer ends with the intake side having a honeycomb screen
- electronics that convert the current draw, to maintain the heated elements temperature, to a frequency to be sent to the PCM for processing

The 01 MAFs, including LS6 MAFs, are slightly larger than 97-00 LS1 units, and are complete housings, without MAF ends. This MAF is actually the MAF used on the GM Truck engines, and was adopted from them in 01 for the C5.  (By the way, so was the 6.0 liter truck cam for 01).  There is a wiring difference between 97-00 and 01 MAFs, so be aware of that when modding, because the 01+ MAFs have integrated the IAT sensor into the MAF Housing. All C5 MAFs (except the 02 Z06) have screens in them to help in laminar airflow. The 02 LS6 MAF does not. It was removed because GM believes the location of the MAF assembly so far forward near the filter with a screen does not significantly assist in helping smooth airflow, at least when compared to the power the 02 LS6 is making, and the need for more air.

The MAF measures airflow by maintaining a constant temperature on wire elements inside the MAF housing. When airflow increases, the wires attempt to cool, and the current draw needed to maintain the temperature, is converted into a frequency and sent to the PCM for further processing. The PCM contains algorithms that interpret the signal received via the MAF sensor. It then increases or decreases fuel injector pulse width signals, thus increasing or decreasing the a/f ratio. In true closed loop mode (part throttle operation), the PCM uses the O2 sensors to insure that it is mixing the a/f mixture properly, and it will adjust fuel trims accordingly to achieve a 14.7 stoichometric a/f ratio. This ratio is the scientific ratio where 100 percent of fuel is utilized when 14.7 parts of air is mixed with 1 part of fuel. This achieves the best compromise of fuel economy and power.

Throttle Body

I think porting the TB is not worth the money on a stock motor. I do think smoothing it out, and removing any turbulent causing items, does help smooth out and increase airflow. a/f should only be slightly effected.

Air/Fuel Ratios, and their effect on power output

Due to the nature of the internal combustion engine, it produces maximum power on a slightly richer mixture than 14.7 - around 13 parts of air to one part of fuel will satisfy most engines. Maximum economy occurs on a mixture that is slightly leaner than the chemically correct proportion - around 16:1. Under normal operating conditions, the fuel system has to regulate the mixture around these two points, depending on whether we demand power from the engine, or are just cruising at a steady speed on the highway.

From the graph it is clear that mixtures richer than about 13:1 will only succeed in wasting fuel : one part of fuel will burn up 14.7 parts of air. If we add two parts of fuel to 14.7 parts of air, only one part of fuel will burn up and do work, because there is not enough air for the second part of fuel to burn. A very important point to note, is that the second part of fuel, which is not going to do any work, takes up space in the combustion chamber – valuable space which could have been filled by a combustible mixture. So, where we could have had a combustion chamber that was filled 100% with a combustible mixture, we now only have about 80% of that space available. The other 20% is taken up by excess fuel, which is not going to burn. That leaves us with an engine that will only deliver 80% of the power it is capable of, while using twice the amount of fuel it should. This explanation finally dispels the "more fuel, more power" - myth. If we want more power, we need to fill the combustion chamber with more "mixture".

Another aspect of tuning "rich or lean" comes down to your reference point of what is rich or lean.

How does it effect power?  Lets take a look:



Above we can now see why the PCM does not concern itself, nor is it restricted to EPA restrictions during WOT operation.  Thats why the mode is called "FUEL enrichment mode"  :)

Back to the C5; If the proper ratio is not being maintained based on O2 input, the PCM will begin to adjust the short term fuel trims. This means the PCM will increase or decrease the injector pulse width based on a too lean or rich condition. If the PCM has to adjust for this condition long enough in the short term fuel trims, it will make an update to the long term fuel trims, and set the short term fuel trims back to 0.

Fuel trims are simply tuning parameters inside the PCM that the PCM updates based on information from the Oxygen Sensors.

Fuel Metering Modes of Operation

    Short Term Fuel Trim Description

The short term fuel trim (FT) is a PCM erasable memory register. The neutral value for the short term FT is 0 percent. Any deviation from 0 percent indicates the short term FT is changing the injector pulse width. The amount of pulse width change depends on how far the short term fuel trim value is from 0 percent. The short term FT is rich when the scan tool indicates a negative number. The short FT is lean when the scan tool indicates a number greater than 0. The short term FT changes the injector pulse width by adding to or subtracting from the base pulse width equation. As the PCM monitors the oxygen sensors input, it is constantly varying the short term FT value. The value is updated very quickly, therefore the short term FT only corrects for short term mixture trends. The correction of long term mixture trends is the function of long term FT.

When the PCM determines that the short term FT is out of the operating range, 1 of the following DTCs will set:

DTC P0171 FT System Lean Bank 1
DTC P0172 FT System Rich Bank 1
DTC P0174 FT System Lean Bank 2
DTC P0175 FT System Rich Bank 2

    Long Term Fuel Trim Description

The long term fuel trim (FT) is a matrix of cells arranged by RPM and MAP. Each cell of the long term FT is a register like the short term FT. As the engine operating conditions change, the PCM will switch from cell to cell to determine what long term FT factor to use in the base pulse width equation.

While in any given cell, the PCM also monitors the short term FT. If the short term FT is far enough from 0 percent, the PCM will change the long term FT value. Once the long term FT value is changed, it should force the short term FT back toward 0 percent. If the mixture is still not correct (as judged by the PCM), the short term FT will continue to have a large deviation from the ideal 0 percent. In this case, the long term FT value will continue to change until the short term FT becomes balanced. Both the short term FT and long term FT have limits, which vary by calibration. If the mixture is off enough so that long term FT reaches the limit of its control and still cannot correct the condition, the short term FT would also go to its limit of control in the same direction. If the mixture is still not corrected by both short term FT and long term FT at their extreme values, a FT DTC will likely result. When the PCM determines that the long term FT is out of the operating range, the following DTCs will set:

DTC P0171 FT System Lean Bank 1
DTC P0172 FT System Rich Bank 1
DTC P0174 FT System Lean Bank 2
DTC P0175 FT System Rich Bank 2

Under the conditions of power enrichment, the PCM sets the short term FT to 0 percent and freezes it there until power enrichment is no longer in effect. This is done so the Closed Loop factor and the long term FT will not try to correct for the commanded richness of power enrichment.

The ability of the PCM to increase or decrease long term fuel trim adjustments is +/- 25% in either direction (23% and 13% for 01's). It will set a diagnostic code. At that point, you are forced to look at your system and either remedy it by go back to where you were, or tuning your system, and/or adding larger injectors, etc.

Fuel Cells

The PCM will move from cell to cell under varying conditions.
There are 22 Fuel Cells, and are as follows:

1-19 – used to update fuel trims
20 – Idle Cell
21 – Deceleration Cell
22 – WOT (Power Enrichment mode)

Timing and Fuel Tables

The LS1 and other modern engines use Timing and Fuel Tables inside the PCM.  They look like the following:


Effects of porting the MAF

When you port your MAF, you do several things to the system.

First by removing the screen, you increase airflow. By doing this however, you somewhat decrease the laminar (smooth) airflow across the MAF elements in the housing. The increase in airflow though, typically offsets the increase in turbulence, so it’s a good mod. Vendors are now including airfoils with their MAF ends to reestablish a smoother airflow.

Porting your MAF either by MAF ends, physical porting, or adding a completely new housing, increases air volume into the motor, but decreases air velocity. Also, unmetered air bypasses the MAF elements. This conflicts with the algorithms in the PCM since air velocity changes, and unmetered air gets by.

You in effect have "tricked" the PCM and created a lean condition because you now have more parts of air relative to fuel. In closed loop mode, the PCM will fix the problem because the O2 sensors will realize the lean condition and the PCM will update the short term fuel descriptions, and eventually the longterm fuel descriptions, if the anomaly is maintained. This in effect forces the PCM to operate in a constant state of modifying the a/f mixture in long term fuel trims from its neutral state without further tuning/modding.

There are several “modes” of operation:

The PCM looks at voltages from several sensors to determine how much fuel to give the engine. The fuel is delivered under one of several conditions called modes. The PCM controls all modes.

Wide Open Throttle Operation

Something to note: The PCM on GEN III engines only operates in True Open Loop Mode during cold engine startup because the heated O2 sensors need time to warm up to operating temperatures. Cold startup is where the engine runs in speed density mode, whereby it only looks at map/maf sensors, and other information such as engine speed and throttle position. Then it goes into, closed loop mode, but has a Power Enrichment Mode for WOT operation.  This mode of operation is a modified version of Speed Density still relying heavily on the MAF for airflow metering to determine engine load, but does not send updates to the PCM like fuel trim adjustments.

Starting Mode
With the ignition switch in the ON position (before engaging the starter), the PCM energizes the fuel pump relay for 2 seconds allowing the fuel pump to build up pressure. The PCM first checks speed density, then switches to the mass air flow (MAF) sensor. The PCM also uses the engine coolant temperature (ECT), throttle position (TP), and manifold absolute pressure (MAP) sensors to determine the proper air/fuel ratio for starting. The PCM controls the amount of fuel delivered in the starting mode by changing the pulse width of the injectors. This is done by pulsing the injectors for very short times.

Clear Flood Mode
If the engine floods, clear the engine by pushing the accelerator pedal down to the floor and then crank the engine. The PCM reduces the injector pulse width in order to increase the air to fuel ratio. The PCM holds this injector rate as long as the throttle stays wide open and the engine speed is below a predetermined RPM. If the throttle is not held wide open, the PCM returns to the starting mode.

Run Mode
The run mode has 2 conditions called Open Loop and Closed Loop. When the engine is first started, and engine speed is above a predetermined RPM, the system begins Open Loop operation. The PCM ignores the signal from the HO2S and calculates the air/fuel ratio based on inputs from the ECT, MAF, MAP, and TP sensors. The system stays in Open Loop until meeting the following conditions:

Both HO2S have varying voltage output, showing that they are hot enough to operate properly. This depends upon the engine temperature.
The ECT sensor is above a specified temperature.
A specific amount of time has elapsed after starting the engine.
Specific values for the above conditions exist for each different engine, and are stored in the electrically erasable programmable read only memory (EEPROM). The system begins Closed Loop operation after reaching these values. In Closed Loop, the PCM calculates the air/fuel ratio (injector on-time) based on the signal from various sensors, but mainly from the HO2S. This allows the air/fuel ratio to stay very close to 14.7:1.

Acceleration Mode
When the driver pushes on the accelerator pedal, airflow into the cylinders increases rapidly, while fuel flow tends to lag behind. To prevent possible hesitation, the PCM increases the pulse width to the injectors to provide extra fuel during acceleration. The PCM determines the amount of fuel required based upon the throttle position, the coolant temperature, the manifold air pressure, the mass airflow, and the engine speed.

Deceleration Mode
When the driver releases the accelerator pedal, airflow into the engine is reduced. The PCM looks at the corresponding changes in throttle position, manifold air pressure and mass airflow. The PCM shuts OFF fuel completely if the deceleration is very rapid, or for long periods (such as long closed throttle coast-down). The fuel shuts OFF in order to protect the catalytic converters.

Battery Voltage Correction Mode
When the battery voltage is low, the PCM compensates for the weak spark delivered by the ignition system in the following ways:

Increasing the amount of fuel delivered
Increasing the idle RPM
Increasing the ignition dwell time

Fuel Cutoff Mode
The PCM cuts off fuel from the fuel injectors when certain conditions are met. This fuel shut off mode protects the powertrain from damage, and improves drivability. The control module disables the injectors under the following conditions:

The ignition is OFF (prevents engine run-on)
The ignition is ON but there is no ignition reference signal (prevents flooding or backfiring)
The engine speed is too high (above red line)
The vehicle speed is too high (above rated tire speed) (Does not apply to Y Cars)
During an extended, high speed, closed throttle coast down (reduces emissions and increases engine braking)

Power Enrichment Mode

When going to WOT or Power Enrichment Mode. The PCM does several things.

It no longer is concerned with maintaining economical or environmental operations. It freezes the fuel trim adjustments, stops monitoring the O2 sensors, and looks briefly where it was at in “closed loop mode”.

It then starts to rely almost exclusively on the MAF sensor input for proper a/f adjustment.

Here is where we are most concerned. Since we have modified our stock MAF, all the conditions of unmetered air, decreased air velocity, etc, that we created with our mods, cause the system to be out of adjustment, in power enrichment mode.

To solve this problem, we need to increase the injector flow rate. To do this, we can either have custom PCM programming done, which modifies the a/f tables in the PCM to accommodate the difference in airflow. Or we can modify the signal before it enters the PCM for processing by tricking the PCM into perceiving there is a greater or lesser load being reported.

In this mode the PCM will add fuel as a percentage, greater than it would normally during PE Mode, if the Ltrims are positive (correcting for a lean condition).  However if the Ltrims are correcting for a rich condition (when they are negative), then the PCM will not take away any percentage of fuel that it normally adds during PE mode.

You will find that if you are running positive Ltrims during non PE mode, and you go WOT, you will see a correlating locked positive Ltrim value at WOT. On the other hand, you will see the trims locked at 0 if you normally have negative Ltrims during non WOT.

MAF Translator, GMS, and MAF Operation

The stock MAF sensor consists of 3 wires. A ground, power source, and a signal wire.

Let's look at how the GMS or MAF Translator work.

The GMS (granatelli) is a complete MAF Sensor with its own customized fixed electronics. It's electronics are preset to adjust the change in airflow based on it's MAF's physical characteristics, and sends what it believes to be the appropriate signal to the PCM for proper fuel adjustments. It seems to be pretty successful in doing this, as long as there are no other variables in the system such as other mods like headers etc.

The MAF Translator is a little more involved, but allows more flexibility.

The MAF Translator consists of a microcontroller (mini stand alone computer), which takes the stock MAF signal, and reinterprets it before the PCM sees it.

The MAFT has two potentiometers on it (variable resistors) that allow the user to skew the signal one-way or the other.

This is a photo of the MAF translator board that resides in the box. Notice the two variable resistors on the bottom. Note: all mode switches should be set to off on the C5

The first POT, is the BASE POT. It is the fundamental signal adjustment, and is present throughout, including WOT. The second POT is the WOT POT. It is utilized when the MAFT senses a WOT load from the MAF. It combines to further skew the BASE signal for fine tuning of WOT a/f operation.

Here is a frequency breakdown of MAFT operation: (courtesy of 'Topless Texan' of corvette forum)

For F-in < 8 kHz

    F-out = F-in * (0.03440 * BASE + 1)
For Fin >= 8 kHz
    F-out = F-in * (0.03440 * BASE + 1) * (0.00407 * WOT + 1)

When changing values on the BASE setting of the translator you are changing the signal across the whole range.  At > than 8K you are adding in WOT settings to BASE for WOT operation.  This allows fine tuning of WOT.

The PCM will not "learn out" the settings of the MAFT on the BASE.  What will happen however is a permanent change in Long Term Fuel Trims.  This will most directly effect perceived engine load and timing.  Remember that no matter what, the O2 sensors rule in 'closed loop' mode, and will always tell the PCM to adjust to 14.7 stociometric a/f ratio.  The MAFT setting during fuel enrichment (WOT) however will always be permanent since the PCM freezes any possibility of updating its fuel trims or any other values.  In this mode the PCM solely relies on raw flow data from the MAF, RPM, and TPS.  This is what makes the MAFT a very good product.

How long does it take for Long Term Fuel Trims to update and set Short Term to 0?  That is really dependent on too many factors to make a specific determination.  I have seen it take up to 250 miles of driving to fully normalize the system after tuning the BASE on the MAFT.  The WOT happens immediatly.

Fuel Cells

You need to analyze your fuel trims (cells 0-19) only, for dialing in the BASE setting on your MAFT, and you analyze your O2 sensors only, for WOT tweaking. Remember, that the stock narrow-band O2 sensors are not precision devices, and should be baselined against a Wide Band O2 sensor at a dyno shop, before you begin tuning.

Custom PCM programming is great, and offers other features separate from a/f tuning, but the drawback is that you have to wait to get a new program each time from the vendor.  (update Jan 2002)  LS1 Edit is out and looks extremely promising as a tool for the home user, without need of hiring a PCM tuner to give you a program.  However the learning curve may be somewhat steep for beginners.

Larger injectors and Why

Another approach to providing the proper fuel needed when porting your MAF is adding larger than stock fuel injectors.

Lets first look at various injector flow rates:

Most injectors will max out at 80% duty cycle and this is the accepted industry standard.
B.S.F.C is brake specific fuel consumption - How much fuel you are using per horsepower per hour.


.50 = B.S.F.C (Brake Specific Fuel Consumption)
In most cases a naturally aspirated engine will have a B.S.F.C of .50. This means that the engine will use .50 lbs. of fuel per hour for each horsepower it produces. Turbocharged engines will want to be at .60 lbs. per hour or higher.

(Inj. Size lb/hr) x (Duty Cycle) / .50 = HP rating per injector

C5 Corvette:

97-98 = 28.4 lbs/hr
80% duty cycle rating: 45.44 Crank HP x 8 = 363.52 Crank HP
100% duty cycle rating: 56.8 Crank HP x 8 = 454.4 Crank HP

99-2001 = 26.4 lbs/hr
80% duty cycle rating: 42.24 Crank HP x 8 = 337.92 Crank HP
100% duty cycle rating: 52.8 Crank HP x 8 = 422.4 Crank HP

Z06 = 28.2 lbs/hr
80% duty cycle rating: 45.12 Crank HP x 8 = 360.96 Crank HP
100% duty cycle rating: 56.4 Crank HP x 8 = 451.2 Crank HP

30 lbs/hr SVO = 36.12 lbs/hr (LS1 at 58psi)
80% duty cycle rating: 57.79 Crank HP x 8 = 462.33 Crank HP
100% duty cycle rating: 72.24 Crank HP x 8 = 577.92 Crank HP


(While .50 is used as the industry standard for calculating and determining an injectors HP ability. High Performance Engines and Racing engines begin to use less than .50

.48, or even .40 in extremely high output.

So with the LS1, there is a margin there below .50

It's difficult to determine precise BSFC needs on an individual basis, because the process involves extensive dyno testing, and the use of lambda meters to observe and log specific air fuel ratios under all conditions.

Also to note, an engine will be most efficient at peak torque.)

As you can see the 30 lbs/hr SVO injectors provide a lot of versatility. Since most ported MAFs typically lean the system out 10 to 15%, the SVO pieces actually bring you back over into a too rich condition (or as I like to say, enough to purposefully overdo it).

This is what we are after. Since the PCM determines the timing curve to use based on engine load, we can now use a MAF Translator to dial in "leanness" or "less of a perceived engine load". Since the PCM doesn’t know the larger than stock injectors are in there, they flow more fuel. Yes, the O2's will adjust for the extra fuel flow via the fuel trims, but the WOT will again be skewed along with the fuel trims. So we have tricked the PCM with our larger injectors. By dialing in leanness, (less perceived engine load), on the MAFT, the PCM will increase the aggressiveness of the timing. Or in other words, it will advance the timing. That is ok, because we are getting the necessary fuel, so pre-ignition, or knock should not occur. We can dial out knock if necessary.

The nice thing about the SVO racing injectors, is that they are also able to grow with our engine if we happen to need the extra HP ability of them. They are also much more robust and quieter than the stock ones.  They maintain the same 10 degree conical spray pattern, and are distanced in the same position over the hot intake valve.  They also have the same impedance rating etc of the stock units.  In fact, they are the exact same type of injector, only they flow more fuel.

Here is a visual comparison with the SVO unit on the left:

Note: Fooling around with injectors is not for all. It’s for those looking to maximize output. Don’t expect any major gains on a stock motor.

Couple of things about Dynoing your car and using a Wide-Band O2 Sensor:

Remember that when you dyno, you can't make changes to your BASE setting on the MAF translator, and expect to see a permanent gain.  If you understand the fundamentals of Short and Long Term Fuel Metering.  You know that they require time to normalize.  In most cases 40 - 100 Miles of spirited driving between tuning sessions. WOT settings on the MAFT can however be changed while dynoing to identify gains or losses.

Tuning:  One of the best tools for tuning your system, is an ODB-II scanner.  This connects to your vehicles ODB-II port under the steering column, and you can observe and log 100's of parameters in real-time.  Most importantly you can monitor your Fuel Trims, and Oxygen Sensors, and tune your engine accordingly.  It is a must have tool for tuning.  I prefer Autotap.  Something to consider.  The heated oxygen sensors used today, are quite accurate at low voltages which occur during closed loop operation.  However they become less accurate during WOT operation.  They should however remain fairly consistent, for this reason, it is important to Dyno your vehicle every so often to get a baseline with a Wide Band O2 sensor to see where they compare.  It is also important to consider that taking reading before and after the catalytic converters can be different since there is a catalyst action occurring on the exhaust gases. so keep this in mind.  The best location to place a wide band O2 sensor is in the exhaust stream before the cats.  Some drill holes in their exhaust for this purpose, some remove their precat O2 sensors and use that boss.  Speak with your dyno operator for the best placement.

Personal Opinions:

The first performance mod I would recommend for anyone is a cold air system. I am partial to the Vortex Rammer, for a few reasons. The Vortex uses a round filter with a inwardly shaped conical front that allows very efficient airflow and increase laminar (smooth) flow.


It also sets up high. Almost where the stock box sits, so water ingestion is as much / or as little of an issue, as with the stock box. Also, remember, that the C5 will never generate enough speed where it creates any sort of ram effect or positive atmosphere. The most substantial gain from a aftermarket filter comes first in removing the restricted stock box. Then you pick up the rest from exposing your filter to cold air. As you accelerate your intake air temperatures will decrease a lot. I would say you pick up power from a cold air system where 80% is from unshrouding, and 20% is from cold air exposure.

The second mod i would do, is long tube headers. Cold air and headers will in most cases net you a solid 35 to 40+ HP to the rear wheels. Thats real power. Headers are one of the most expensive bolt on mods at around 1200 with install. But by the time you nickle and dime other mods onto your C5, you will go over 1200 pretty quick. Guys with 4 CATS like 01's will see a larger return by removing the precats with the long tube header install.

Beyond that, bolt on mods become thrown into what I call an "additive" group. For instance, I believe there is merit in the throttle body bypass, powerducts, ported mafs, etc. But the HP increase is small for each. All together though, and they can add up to something worthwhile.

Exhausts will typically yield 0 to 8 HP on a basically stock motor. Do not buy exhausts expecting performance increases. Buy them for looks and sound first. And anything you get will be a pleasant addition.

Other solid HP and ET gainers are:


As you can see, the whole system is quite involved. But it becomes more and more simple if you break it down. An internal combustion engine functions on the same fundamental principles of physics as it did since inception. Often times, the most difficult process in learning and understanding it, and its electronics, is the difficulty of most to, “dumb” themselves down enough, to understand it.

Good luck to you and your modding!




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