The modern fuel-injected racing engine is a far cry from carbureted engines of the past. Through the use of ever-improving electronic controls, engines can be made to perform more precisely and consistently to ensure the user of a positive experience when the chips are down and the win light is the ultimate goal.
EngineLabs has been lucky enough to establish a relationship with one of the premier engine calibrators, noted MoTeC tuner Shane Tecklenburg of Tuned By Shane T. Recently we cornered Shane in an effort to discuss some of the important items to look for when one is calibrating an engine, be it a brand-new build making its first appearance on the engine dynamometer or an engine that’s already installed in a vehicle and making laps on the track.
Tecklenburg has a long and storied history with racing engines of all types; his customers range from the Toyota Supra Pro Import quarter-mile world record holder Ekanoo Racing (6.04 at 240.8 mph), the UK’s Andy Frost, owner of Red Victor 3, the second-quickest street-legal car in the world (save for Larry Larson), and even Bonneville competitor Roger Lessman, who competes on the salt with his compressed natural gas Streamliner. Tecklenburg has also spent time tickling the keys on Mark Heidaker’s impressive 278 mph Texas Mile Ford GT, among other customers located all over the world.
Tecklenburg’s skills are highly sought after, but he’s one of the most unassuming folks we’ve had the opportunity to work with over the years. He’s impressed upon us that not only is engine calibration extremely important, but it’s also the entire package that makes a racecar.
Read on for some of his tips about what to look for during the initial calibration and subsequent fuel injection tuning processes in order to ensure a smooth-running, high-performance engine.
These processes are not limited to MoTeC engine management systems, and can be used no matter the system on the engine as the concepts are the same.
Injectors, Injectors, Injectors
You’re wondering why a fuel delivery component is at the top of Tecklenburg’s list for an EFI tuning article, and the answer is quite simple.
“The injector is the interface between all of your expensive, sophisticated and highly accurate electronics and your engine. This has got to be the most overlooked item in any aftermarket EFI system,” he explains.
Unless the injector can perform as required – that is, to spray fuel in the required amount at the proper time – the rest of the tuning processes will not perform as required. The engine management system makes the assumption that when a certain volume of fuel is requested from the injector that exact volume is what actually gets delivered.
“It has been taken for granted that the injectors, seemingly a simple device, actually do what you tell them to do. We find that they in fact do not always do what it is asked. Surprisingly I’m not talking about spray pattern, cone angle or droplet size here; those things are all subject to application. I’m talking about the fundamental thing we require from an electronic injector, that is to deliver a specific volume of fuel or gas when asked to do so,” states Tecklenburg.
Other variables can allow the injector performance to differ from what is expected. Battery voltage and differential fuel pressure are among these variables. Differential fuel pressure is expressed as the difference in pressure across the injector from the fuel rail to the manifold pressure it is spraying into. It is essential to the operation of an EFI system that the fuel pressure regulator maintain a constant differential fuel pressure so that the only influence on injector flow volume is the amount of time in which it is turned on.
“Differential fuel pressure affects how much volume actually comes out for a certain pulse width, but there is also a ‘Dead Time’ or ‘Offset’ from what is commanded to the injector versus what is actually delivered. This Dead Time is due to the fact that the injector cannot instantaneously begin flowing fuel when it is triggered and also does not instantaneously stop flowing fuel when the trigger is removed. The Dead Time also varies based on the system Battery Voltage and the differential fuel pressure. Fortunately the ‘Engine Management System’ or EMS, has a battery offset table which can be populated with the proper Offset values as supplied by the injector manufacturer. Once the correct Offset data are entered, the linear calculations that the EMS does to determine the correct fuel volume required will be accurate, so long as the injector flow curve is actually linear,” he says.
Is it truly linear?
Here’s where the second problem comes in – that injector flow may not actually be linear at all. If it is not, there will be an error in the commanded fuel volume and the actual fuel volume due to the incorrect data entered into the EMS. The problem can be overlooked if the injectors have been flow matched and characterized based on linearity across the entire operating range, since the error will be insignificant.
However, if the injectors have only been matched at Static or Wide Open flow rating, there may be huge variations across the rest of the operating range, and one can imagine the difficulty injectors that aren’t matched will provide to the tuner during the process.
During our conversation, Tecklenburg used the analogy of a V8 engine with eight separate carburetors, each with different air bleeds, main jets, and randomly different idle, transition, and acceleration circuits, and the difficulties that engine might pose during the tuning process.
“Bottom line here, buy your injectors from a supplier who can provide you with not only the Offset data, but also the Linearization data of the injector over its entire operating range. If you request this information from a supplier or manufacturer who cannot or will not provide it, thank them and then turn and run the opposite direction,” says Tecklenburg.
Wiring Loom, Wiring Loom, Wiring Loom
Now that the injectors are sorted out, it’s time to get the system into the car to go racing; here’s another major area of concern.
“This should be totally obvious, but the greatest system in the world cannot deliver proper results without the wiring system holding up its end of the bargain. The wiring is the network that communicates all the accurate signals into and out of your EMS,” he notes.
The wiring will be subjected to heat cycles, plenty of vibration, and the occasional crew member forgetting to disconnect the loom from the engine or transmission prior to removal. Put simply, it must be robust to ensure it will live in an automotive racing application.
We’ve all seen the in-car videos on some of the world’s quickest and fastest vehicles, where the camera looks like it might vibrate off its mount at any time; just think about the wiring looms and how they must endure those conditions, day after day, round after round, in the heat and potentially in the cold, and not fail.
Better yet, they must excel to ensure consistently high levels of engine performance.
I have developed a philosophy. It says ‘give the engine what it wants and invent a theory as to why later’. – Shane Tecklenburg, Tuned By Shane T
He also notes that complicated systems with many different sensors and components are often best wired by a professional with the experience to properly design and blueprint a system. Much like the engine itself, the wiring loom is paramount to performance.
Estimation Of Air And Fuel – Do Your Math
Assume...Sometimes
There are a few assumptions to be made during the tuning process, which reflect known-good items. Firstly, that the engine is 100% efficient, and that efficiency will exist at 4,500 rpm. Secondly, we’ll assume sea level air density of .0746 pounds per cubic foot. Third, that the throttle is wide open as it would be on a dyno pull.
Making these assumptions is not a leap of faith, rather, they are truths that will permit the rest of the calculations to be performed with a measure of confidence.
Well, almost.
He recommends breaking out the calculator to do a bit of math – this will give you an idea of what to expect during the tuning process. By breaking down the information into steps, it allows for a greater understanding of what one is trying to achieve during the tuning process.
“The goal of any calibration is to match the required mass of fuel to the mass of air that the engine is able to consume to arrive at the correct air fuel ratio under all operating conditions,” he says.
“If the air mass was a known quantity, this would be easy, but it’s not. And that’s where the math comes in. It’s helpful if we can make some assumptions and do a quick calculation or two so we have a cross reference point to check against as we do the actual calibrating.”
Here is an example engine. It’s a 350 cubic inch naturally aspirated small-block Chevrolet, running VP C16 race fuel. It’s using Injector Dynamics ID1000 (1015cc/min @ 43.5 psi), and has a desired A/F ratio at efficiency peak of 12.6:1.
- Step 1: Solve For Air Mass
Cycles per minute = RPM/2, 2250 in this example with a starting point of 4,500 rpm
Engine Volume = Cycles Per Minute X Displacement
2250 X 350 = 787,500 cubic inches/minute or 455 cubic feet/minute
Air Mass = Engine Volume X Air Density
455 X .0746 = 33.943 pounds/minute - Step 2: Solve For Fuel Mass
Required Fuel Mass = Air Mass/Desired Air Fuel Ratio
33.943/12.6 = 2.693 pounds/minute or 161.58 pounds per hour - Step 3: Convert Known Injector Flow Volume into Mass in pounds/hour
Total Fuel Mass = Volume for all injectors X specific gravity x 60 / 453.6
1015 X 8 X .735 X 60/453.6 = 789.44 pounds per hour - Step 4: Determine percentage of total injector flow current conditions will require
Flow Percent = Required Fuel Mass / Total Fuel Mass
161.58 / 789.44 = .2046 or 20.46% - Step 5: Determine Injector Cycle Time at current Operating Speed
Cycle Time = 1000 mS / (Cycles per Minute / 60)
1000 / (2250/60) = 26.66 milliseconds - Step 6: Convert Injector Flow Percentage Into Effective Pulse Width
Effective Pulsewidth = Flow Percent X Cycle Time
.2046 X 26.66 = 5.454 mS
“These results mean we can expect the engine management system to deliver a 5.454 millisecond long pulse (before the battery offset is added) at full throttle and 4,500 rpm. We will expect then to have an air fuel ratio of 12.6:1 when this happens, assuming the engine volumetric efficiency is 100%” says Tecklenburg.
“This now gives us a guide to either pre-program the ECU for that operation or to at least have a reasonable guess what to expect when we reach that operating point. If the engine is richer than 12.6:1 at that operating point, and the pulse width, battery offset and fuel pressure are correct, then the engine’s volumetric efficiency is less than 100% efficient. In fact, the percentage you have to adjust the fuel delivery table by to achieve 12.6:1 is also the amount less or more than 100 that your engine volumetric efficiency is.”
What Does The Engine Want?
The entire goal of the calibration process is to optimize the performance of the engine. Calibrate the engine to what it wants, not what you think it needs.
“It’s not to make particular sensors read a specific value, or to satisfy your preconceived notion of what the engine should want under particular conditions, or what your buddy’s engine wanted that was ‘almost the same’ as yours,” says Tecklenburg.
Far from it, in fact. He stresses that the most important thing you can do is pay attention to all of your senses while working on the engine calibration – not just put your head down in the sand and think ‘but it’s supposed to be doing this.’
Before any change is made, it’s a wise idea to analyze it and think about the expected result of the change if it were to be made. Finally, if the change you make does not reach the desired result, he suggests going in the opposite direction.
“Between them you should be able to pick the middle ground. This would include adjustments for fueling, ignition lead and boost. Always concentrate on a plus and minus and try to leave your final calibration in the mid point. This will leave you with a calibration that leaves little room for improvement while also operating within safe limits,” he says.
“I have been on the dyno calibrating an engine when the readings from all of my sensors indicated one thing, yet the dyno indicated another. When in doubt, believe the dyno – it’s the device relaying to you what your engine is trying to tell you,” he sums up. “In my 14-plus years calibrating racing engines, I have developed a philosophy. It says ‘give the engine what it wants and invent a theory as to why later’.”