Introduction to Engine Tuning

Before this book even begins, I wish to make it perfectly clear that this is not an engine design or combustion theory text. The goal here is for the educated enthusiast, skilled technician, and automotive engineer alike to all be able to come away with something. To this end, we explore the basics of engine operation to reinforce what is really going on under the hood. From there, we move on to the “ins and outs” of modern electronic fuel injection systems and ultimately some specifics of calibration methods and horsepower production. The focus of this book is gasoline engines; however, many of the concepts can carry over to other applications. While much of the material may seem like a review to many, it is important to keep in mind the fundamentals of engine operation while attempting to change calibrations. A solid understanding of what is happening inside the manifold and combustion chamber gives the calibrator an edge in tuning.

 


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Let’s face it, today’s performance enthusiast doesn’t want to compromise. We want tons of power, reliability, drivability, and worry-free operation. Gone are the days of living with the compromises between the horsepower seekers and the emissions regulators. We now live in a time where one can walk into a new car dealership and simply buy an honest 400-horsepower car that idles quietly, drives smooth as silk, and is backed by a full factory warranty. Considering that in the heyday of the muscle car wars 300 gross horsepower was astounding and it still came with a rough idle and terrible gas mileage, today’s performance car market is as good as it has ever been.

 

The 1968 Plymouth GTX 440 made 375 gross hp and was considered state of the art for its time. In reality, this engine has a specific output of 0.85 hp per cubic inch and would fail modern emissions tests miserably. (Nate Tovey)

The 1968 Plymouth GTX 440 made 375 gross hp and was considered state of the art for its time. In reality, this engine has a specific output of 0.85 hp per cubic inch and would fail modern emissions tests miserably. (Nate Tovey)

 

The 2006 Ford Mustang makes 300 hp out of a 281 cubic engine for a specific output of 1.07 hp/ci, with complete compliance to today’s stringent emissions standards. (Nate Tovey)

The 2006 Ford Mustang makes 300 hp out of a 281 cubic engine for a specific output of 1.07 hp/ci, with complete compliance to today’s stringent emissions standards. (Nate Tovey)

 

The engine in this Mercedes 220SE is equipped with mechanical fuel injection and makes about 120 hp from 2.2 liters. It has limited capability to adjust for changing weather conditions. (Nate Tovey)

The engine in this Mercedes 220SE is equipped with mechanical fuel injection and makes about 120 hp from 2.2 liters. It has limited capability to adjust for changing weather conditions. (Nate Tovey)

 

So how did we get here? First and foremost, the automakers have learned a thing or two about engine design in the last three decades. Serious advances in the areas of cylinder head, intake, and camshaft design have allowed engines to make far more power out of much smaller packages and displacements. What the OEM engineers call specific output, or power per cubic inch, has gone way up directly as a result of the increase in flow potential of modern component designs. Compare today’s injection molded long runner intake with the castiron four-barrel paperweight of the ’60s and it’s easy to see the difference. Other than the obvious weight advantage, the port walls are smoother and sizes are tuned to take advantage of standing waves to increase port energy at the same time the valves are opening. Friction has become another area where modern engines have evolved tremendously. Where there were once solid tappets dragging across an oiled cam under severe spring pressure, there are now hydraulically damped rollers or even the complete lack of pushrods shortening the path between the cam lobe and valve. Looking at a modern cylinder head also reveals carefully designed port geometry, combustion chambers designed to do more than simply seal ports, and often a camshaft or two. The head ports themselves have evolved to increase velocity, yielding more total flow through smaller valves and better mixing of the air and fuel in the combustion chamber.

 

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With that said, efficiently designed air pumps don’t run as a working engine without a little help. Current production vehicles run on electronic fuel injection for a whole list of reasons, not the least of which are emissions and drivability. Fortunately, emissions and power production are not completely at odds with one another as the environmentalists would have us believe. The underlying connection is efficiency. Taking advantage of every drop of fuel in the engine leaves less left over to pollute our precious atmosphere and ensures that we’re not missing out on our chance to use the energy in that fuel to push as hard as possible on the piston to move us down the road. The balance is to make sure that we only inject enough fuel to make the power necessary to do whatever it is we’re asking the engine to do at the moment. Whether it’s idling at a stoplight, cruising the interstate, or racing down the quarter mile, there is always an ideal recipe of air and fuel to pour into the engine to keep things working as close to peak efficiency as possible. The closer we can keep the engine to this ideal mix at all times, the better the engine will perform.

 

This modern engine, although still carbureted, produces large amounts of power. But even at over 1,600 hp, it must still be adjusted to accommodate changes in current weather conditions for best performance. (Nate Tovey)

This modern engine, although still carbureted, produces large amounts of power. But even at over 1,600 hp, it must still be adjusted to accommodate changes in current weather conditions for best performance. (Nate Tovey)

 
This Super Street Outlaw engine uses two sets of injectors, each on its own rail, to supply enough fuel to make almost 2,000 hp. With an EFI control system, changes in weather are automatically compensated for by the PCM to keep the engine running at its peak. (Nate Tovey)

This Super Street Outlaw engine uses two sets of injectors, each on its own rail, to supply enough fuel to make almost 2,000 hp. With an EFI control system, changes in weather are automatically compensated for by the PCM to keep the engine running at its peak. (Nate Tovey)

 

Sure, that old small-block Chevy in the garage has run great for years with a single Holley 650 on top and the timing locked at 34 degrees. It makes all the power you need to go out on Friday nights and cruise the memory lane of your choice to your satisfaction on any summer night. So how does it start in March? Why do you need to re-jet the carburetor to run good every October? Why did that new Mustang at the last stoplight walk all over you? How can he do that to your hot rod and still be 100 percent emissions legal?

The answers come in the form of precision. The ability to instantly adjust to changes in conditions is what gives an electronically fuelinjected car the decided advantage here. Carburetors can be tuned perfectly under any single condition. This is why you see drag racers constantly checking their weather stations in the pits between rounds and making adjustments to the jets. With a change in density comes a change in what would be considered an ideal mixture at any given moment. What was spot-on last night can now be five percent rich this afternoon. The beauty of EFI is that changes to the engine’s operating parameters, necessary to keep up with a changing atmosphere, happen without even lifting the hood. Further, the changes that EFI can make are in smaller increments than what can be done with a jet change on a carburetor. It’s not unusual to see adjustments in half a percent of fuel delivery or even a quarter of a degree of spark lead in a modern fuel injection system. The whole trick is to know where to have the controller make these adjustments.

 

6) From left to right: GM GENIII, Siemens SIM90, and Ford EEC-V. All are different packages for the same general set of control functions. (Nate Tovey)

From left to right: GM GENIII, Siemens SIM90, and Ford EEC-V. All are different packages for the same general set of control functions. (Nate Tovey)

 

Modern PCMs pack as much processing power as the desktop computers of several years ago. In the time it took you to read this caption, this processor can perform over 16 million calculations. (Nate Tovey)

Modern PCMs pack as much processing power as the desktop computers of several years ago. In the time it took you to read this caption, this processor can perform over 16 million calculations. (Nate Tovey)

 

The speed at which the electronic processors inside modern Powertrain Control Modules (PCMs) operate is extremely fast, even when compared to the operating speed of an engine at redline. Processor speeds are measured in Megahertz, or millions of cycles per second. Even the most advanced Formula 1 engines today only operate at a maximum of approximately 23,000 rpm. It becomes easy to see how the PCM has plenty of time to think about what outputs to deliver. The PCM can take a snapshot of the engine’s performance at any instant, analyze every parameter, and make multiple calculations before the crankshaft even rotates a couple of degrees. This process can be repeated multiple times between combustion events at high speed.

 

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In the early years of electronic fuel injection, control of system and engine operation was reserved for OEM engineers. The added complexity did a good job of scaring many performance enthusiasts away. Little by little the aftermarket began to step up to the plate and embrace the technology. Eventually enthusiasts were rewarded with replacement EPROM (Erasable Programmable Read Only Memory) chips modified to provide the subtle changes to air/fuel mixture and timing needed to squeeze 10 or more horsepower out of production vehicles. After that came the aftermarket’s trump card, the stand-alone fuel injection system. No longer were performance enthusiasts tied to factory fuel and timing maps. New, more exotic combinations of parts could be employed in the name of horsepower.

With the advent of the Internet, we have seen hundreds of enthusiast sites spring up dedicated to just about any performance make, engine, and vehicle imaginable. The question that seems to get echoed across all forums seems to be: “How do I change the PCM to get more out of my car?” Not unlike politics, everyone seems to have their own opinion of what’s best, and nobody seems shy to argue that they are right. While some forums seem to be far more technically oriented and mindful of avoiding the proliferation of misinformation, there seems to be no shortage of armchair quarterbacks in the Internet tuning arena. The best advice here seems to be to take everyone with a grain of salt. It is rare to see true experts online teaching the general public the secrets to their success for free. More often it’s the grassroots enthusiasts sharing what tip or trick most recently worked for them.

The word of caution here is to remember that with the complexity of today’s EFI systems it’s easy to get what seems like the right result for the wrong reason. Many output functions are controlled by layer upon layer of tables, scalars, and functions that work in concert to deliver the seamless operation of the engine. Changing the wrong function or table may indeed correct the problem at hand while unknowingly creating another. The benefit of the EFI system is that the layers of control, if employed correctly, can independently prevent individual performance issues while maintaining a complete package that drives smoothly. Don’t feel bad if this seems intimidating at first; it takes time to fully understand the layers of control in an EFI system. Many systems use slightly different strategies or naming to describe and control the same physical systems. With a little bit of patience and attention to detail, it is possible to tame even the most complicated system.

This book covers a logical approach to EFI calibration. The methods discussed here closely follow those used by OEM calibration engineers on current production vehicles. We cover a solid foundation of proper setup, airflow modeling, and fine-tuning of drivability parameters. This approach works regardless of the EFI system being used. Whether you are reflashing the PCM in a 2005 OBD-II equipped BMW, burning a new chip for a 1992 Mustang, or tuning a dedicated racecar using an Accel DFI GenVII standalone processor, the tuning procedure is fundamentally the same. I encourage the calibrator to constantly think about what is going on inside the combustion chamber when making adjustments. Understanding how much air is making its way into the cylinder and how fast the mixture is burning after ignition goes a long way toward making the right decision when changing engine maps during the calibration procedure. At the end of the day, almost all EFI systems operate on the same set of principles. The processor does not know what kind of car it is running, only what inputs and outputs it has. The same laws of physics and thermodynamics apply to all engines equally. A proficient calibrator can tune any engine as long as he has access to the necessary hardware and software.

Known by many names, engine controllers are still engine controllers. It seems as though almost every manufacturer has its own name for their electronic controller. Examples include Powertrain Control Module (PCM), Engine Control Module (ECM), Engine Control Unit (ECU), and Electronic Engine Controller (EEC). For the sake of simplicity, we use PCM through this text as a generality.

 

Written by Greg Banish and Posted with Permission of CarTechBooks

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