injection timing

Timing Table
The injection timing table has values in Degrees BTDC (compression stroke). When using an M400/M600/M800 you can choose to have either a 2D or 3D Injection Timing table (20 x 11 sites). The Setup Parameter "Injection Timing Position - (itp)" selects Start of Injection or End of Injection. End of Injection is normally best. When using an M4/M48 the Injection Table is a 2D table (20 sites) for End of Injection Timing. The table is found in the Adjust menu under FUEL / Injection Timing.
The Injection Timing may be adjusted at various RPM points and optionally at various Efficiency Points depending on the state of the 'Miscellaneous Setup - Injection Timing Table (itt)' parameter. The injection timing position must be selected to either start of injection or end of injection in the ECU Manager Fuel Setup (M800). It is most common to select the end of injection point as it is easier to relate this to the time the inlet valve closes and it means that the values in the table will have smaller steps. At idle speed a 5ms fuel pulse will have duration of 18 degrees of crankshaft rotation, a 10ms pulse at 3000 RPM will last for 180 degrees and a 10ms pulse at 6000 RPM will last 360 degrees. So for the same end of injection time we would have to have a table with very large differences from one point to the next if we were to use beginning of injection as a timing position. It would also be necessary to have different timing values depending on the length of the injection pulse.

Normally the ideal aim is to inject the fuel with the inlet valve open but we have to take in to account that there is a delay between the time the injector closes and the time the fuel passes through the valve, this delay will vary depending on engine speed and manifold design. The closing rate of the valve and the amount of valve overlap will also have an effect on the ideal fuel timing position.
The best and easiest way to find the ideal fuel timing is by tuning to the richest lambda value. Moving the injection will have an effect on the lambda reading because in-correct timing will cause more of the fuel to condense on the port wall and so will not be burned. As the timing approaches the ideal point the lambda reading will show richer because more if the injected fuel is being burned. A good starting point is to have the timing at around 270 degrees at 1000 RPM and increasing by 20 degrees every 500 RPM until about 4000-5000 RPM where the injection timing is less critical (depending on injector sizing). It is reasonable to expect that this would give the most efficient timing point whether or not there is any gain in performance. The fuel table can then be re-trimmed to give the desired air-fuel mixture. When injector pulse times are long the injection timing will have less effect. To avoid rapid transitions in Injection Timing it is advisable to limit variations between adjacent sites to less than 100 degrees. A value of 0 is the same as a value of 720 i.e. both are Top Dead Centre. The value may be increased past 720 degrees if necessary which allows a transition back through 0 degrees without causing a transition problem. In other words a value of 820 deg. is the same as 100 deg.
It is reasonable to expect that this method will give the most efficient timing point and provide the most accurate control of fuel mixture but there may be applications where this is not going to give the best performance. The main reason for this is fuel atomisation. If the injector is not particularly good at atomising the fuel better results may be found by injecting on a closed inlet valve. This can also be beneficial for engine starting. This will allow the fuel to atomise better in the inlet port prior to induction but will lead to a less precise control of fuel mixture.
When the Injection Timing screen is open and the engine operating point is close to the current cursor position the Injection Timing is forced to the cursor value rather than being interpolated from the adjacent sites, this allows adjustments to be made without the adjacent sites affecting the adjustment value. The quick lambda function may be used to adjust the main fuel table when the Injection Timing screen is open. Some engines (e.g. Subaru) have tumble valves in the inlet manifold to improve the fuel mixing at los speed. Where these are disabled or removed timing the end of injection at about 450 will give best results at idle speed and starting.

Injector Sizing
Typically in a production car an injector is selected to run at around 85% duty cycle at maximum fuel demand. This will normally allow enough resolution in the fuel table at idle speed to provide accurate fuel mixture adjustment and injection pulse times that are not too short. In this case the injection timing will have little effect at high RPM / Load because the injector will be open most of the time, by the time it closes it is nearly time to open again. Bigger injectors can be used which would give shorter injector duration at high speed and take advantage of the benefits of timing the fuel, however this will cause a loss of resolution and very short injection pulses at low speed. This will cause poorer idle quality and starting, particularly when the engine is cold. An alternative to this is to use secondary injectors (Hi/Lo).

Fuel Conditioning and Targeting
Most injectors deliver an atomized fuel spray, and some engines have injectors with a spray pattern specifically tailored to suit the port / valve / injector location for that engine. Some motor sport injectors do not have a spray pattern at all and just squirt fuel in a straight beam. This may not seem like a good idea but where high quantities of fuel are required (particularly when using methanol) it is an effective way of getting a large quantity of fuel into the engine but it relies on swirl in the combustion chamber for good mixing.
Injectors which target fuel directly on to the back of the inlet valve will provide the best control of fuel mixture and response to transient changes. Engines with this type of injector layout will respond very well to injection timing where the injection takes place with the inlet valve open. The deviation from desired air fuel ratio will be reduced with this layout because there is little or no port wetting. The injector’s ability to atomize fuel is critical in this instance because there is no time for the fuel to atomize in the intake manifold. Although this will not effect the mixture stability it may mean that there is higher levels of un-burnt hydrocarbons in the exhaust emission. Timing the injection pulse with the inlet valve closed (exhaust stroke) will improve fuel atomization but deviations from the desired air fuel ratio will be greater because of the effect of the fuel layer that is created on the port wall.
Some engines used in Motorsport have injectors mounted on the air intake side of the throttle. Typically these injectors would be mounted roughly 250 mm away from the valve. Gains in engine performance can be found at higher RPM with this arrangement, this is partly because the fuel has more time to atomize before it reaches the engine. There is also a slight cooling effect generated by the atomized fuel (stand off)in the intake. The disadvantage of this is that there is a large area of the inlet covered by a film of fuel which leads to problems with deviations from the desired air fuel mixture when accelerating and decelerating. Other common problems with this arrangement are fuel stand-off (reversion) and the risk of air box fire. Injection timing can be used to reduce and help control stand-off but is more effective with shorter injector durations.

Idle Stability
Injector timing will have an influence on idle stability as well as tail pipe emissions. It is expected that fuel mixtures need to be a little bit richer at idle and at low load than at cruising speed but this can be minimised by injector targeting and timing. This will vary depending on engine design but is significant particularly when using a closed loop idle control system.

MoTeC Europe Ltd

The Story Behind the Dynojet Chassis Dyno - The Truth Meter

1/4

It's a story as old as hot rodding itself. It starts with the sales pitch-"Buy my widget and your engine will gain 50 hp"-and ends with a disappointed customer with a car that sure doesn't feel like it picked up 50 hp. A dragstrip doesn't offer much proof one way or the other on incremental changes because there are too many variables involved, so the seat of the pants was for a long time the only way to tell if a modification or part really helped. That all changed in the '90s with the introduction of the Dynojet, a portable chassis dyno that was in the financial grasp of most every mom-and-pop performance shop. Finally, power claims were proved or disproved as soon as the stuff was installed. And with the emergence of custom computer tuning, the Dynojet has proven invaluable to these shops; they can now tune the car without ever having to blast up and down a city street. They can thank Mark Dobeck, the machine's creator.
Dobeck got his start tuning English sports cars in a Portland, Oregon, garage in the late '70s. He had hot-rodded the shop's Sun infrared exhaust analyzer to improve response time and became a wiz at using exhaust-gas carbon monoxide to optimize power on the go. The trouble came later when he moved on in 1980 to open a motorcycle shop in Wisconsin. Cars were one thing, but there was no way to haul a gas analyzer as big as a TV set on a motorcycle. So Dobeck talked his inventor/fabricator father into building a stationary rolling-road that could support the rear wheel of a motorcycle on a moving drum so he could continue tuning while "driving" with the big infrared analyzer.
The rolling road was designed with a hydraulic system that could be adjusted to work a bike engine harder at a given speed, something like the resistance controls on a Stairmaster machine. But because Dobeck and his dad were mechanics rather than mathematicians, they made the rolling drum heavy, and the homebuilt dyno had a surprising amount of inertia. It was accidentally pretty good at simulating a motorcycle's ability to accelerate.

2/4 On the road, Dobeck tested a bunch of cars in secret so he could watch the Dynojet 248 in action without too many people knowing what he was doing. The Dynojet often disappointed optimistic enthusiasts and tuners, but it just as often helped find free power.

Dobeck's new bike shop opened just in time for the arrival of Japanese superbikes equipped with constant velocity (CV) carbs, which were new to motorcycling. CV carbs provided good performance, economy, and emissions, but they could not be tuned and jetted using traditional methods. Many people recommended replacing them, a $600 solution. But Dobeck understood CV carbs from the days of wrenching on English cars and modified them to allow the new motorcycles to run with performance pipes and air cleaners. Before long, bikers were traveling from all over the upper Midwest for Dobeck's dyno-jetting service. Meanwhile, in the evenings, Dobeck read magazine stories of hot rod bikes running exhaust-system shootouts on the torque-cell dynos of famous California super tuners.
Performance magazines loved dynamometers because they brought science to hot rodding. But torque-cell dynos, which load an engine by forcing it to pump water or generate electricity, are expensive, and using them has often required removing the engine from the vehicle.
"I started to realize I was doing something that no one else was doing," says Dobeck, who was using his homebuilt inertial dyno to tune bikes with the goal of improving acceleration and responsiveness. "Eventually I built a few jet kits to see what we could do with them."

3/4 The front end of a Chrysler K-car-the cheapest vehicle Dobeck could find-was used to spin up this research chassis dyno at Dynojet. A robotic controller could use the K-car to the spin the dyno drums to high speed to observe balance issues and then leap off the drums to remove all drag.

Dobeck named his company Dynojet. His first big customer was K&N Filters, and it wasn't long before he was selling lots of jet kits. His company grew at a rapid pace, and sure enough, a competitor sprang up with a similar product. "Their advertising was working," Dobeck says. "They were taking away sales. But the product didn't work. Not at all." To prove it, he called several of the top engine-dyno suppliers to see if they would help him develop an affordable version of his homebuilt inertial chassis dyno that could live in the shops of Dynojet dealers to show the world what worked and exactly how well. "Every one of them laughed at me," Dobeck remembers.
One of the biggest headaches of Dynojet's go-it-alone chassis-dyno project was figuring out how to assign meaningful power numbers in the face of unknown inertia from the moving parts of the hundreds or thousands of engine, drivetrain, and tire combinations. Wrestling to fully understand inertia and powertrain losses, Dobeck and his team quickly realized that the standard physics formula of weight, time, and distance for converting acceleration into horsepower simply didn't work-the derived number was always lower than accepted numbers. They poured on resources and burned up time and money investigating it, but no matter what they did, the math never added up.
Dynojet's final number-fudge was arbitrarily based on a number from the most powerful road-going motorcycle of the time, the '85 1,200cc Yamaha VMax. The VMax had 145 advertised factory horsepower, which was far above the raw 90hp number spit out by the formula. Meanwhile, existing aftermarket torque-cell engine dynamometers delivered numbers that clustered around 120. Always a pragmatist, Dobeck finally ordered his Chief Engineer to doctor the math so that the Dynojet 100 measured 120 hp for a stock VMax. And that was that: For once and forever, the power of everything else in the world would be relative to the '85 Yamaha VMax and a fudged imaginary number. Dobeck's engineering staff was dismayed by the decision, but the Dynojet 100 exclusively measured surplus power available to accelerate the vehicle's mass-no more, no less-and that was true even if the modification was a low-inertia flywheel or lightweight wheels. As long as the inertial dyno's numbers were repeatable, the critical question (did a particular modification make the engine accelerate faster or slower?) would be answered correctly.

4/4 Demonstrating the Dynojet 100 bike dyno in communist China, Dobeck entertained these bikers in the hills above Macao.

Dobeck then turned his attention to providing the dyno to bike shops across the country. The first 20 early adopters of Dynojet kits were customers who had defeated the replace-your-CV-carbs drumbeat seven years earlier. "These guys believed in what we were doing," says Dobeck. "I called, said I've got this dyno, and it costs $6,500. And they said, 'Send it.'"
When a small network of the most important dealers had dynos, Dobeck took to the road with a mobile bike dyno mounted in a trailer. He would ask performance-shop owners, "Aren't you sick of being the scapegoat for stuff that doesn't work as advertised?" They were, and they started buying dynos. In subsequent years, Dobeck demonstrated his bike dyno everywhere from Montana to communist China. Then he took on the world of cars.
The pre-Dynojet world of hot rods circa 1993 had a lot of information, misinformation, and disinformation. You can't feel a 5-10hp boost on a car, so many engine modifications were faith-based efforts made with a screwdriver and a prayer. Hot rodding had left more than a few hapless victims with fading dreams of glory and empty pockets. The onset of computerized engine controls in the '80s made increasing horsepower even more complicated-escalating the opportunities for the unscrupulous or incompetent to fleece those with the need for speed: Install this electronic doohickey, double your power. Car guys needed a cost-effective, repeatable B.S. meter every bit as much as bikers. Dobeck hired his dad and put several engineers on the project to handle critical design issues and the team constructed the original Dynojet 248A using two 48-inch-diameter, 1,200-pound rollers, later increased to 1,600 pounds.
When it came time to market the new car dyno, Dobeck realized that although his company was big-time in the motorcycle universe, no one in the door-slammer crowd had ever heard of him. So he went on the road again. The import crowd embraced the new Dynojet first, since they were the victims of a lot of bogus power claims from unscrupulous manufacturers. Then Dobeck visited some of the bigger aftermarket companies. The Dynojet often brought bad news to hot rodders and manufacturers-now everyone on the street knew exactly how much power the parts were worth. But the good news was, in the right hands, the dyno could find "free power" through tuning 8 out of 10 times.
With the automotive aftermarket sold on his Dynojet, Dobeck wanted to relax. By 1996, he was running on fumes and on the road way too much working like a madman. "I had no normal life," he says. An investor group was looking at buying the company, but it was on the fence, so he chased after a NASCAR licensing agreement. Back in the trenches he went, this time to offer his Dynojet to the NASCAR teams in North Carolina. They bit, and after a while, NASCAR agreed to his humble terms and made it "The Official Dynamometer of NASCAR" for three years. The NASCAR teams bought dynos, and Dynojet designed fabulous NASCAR chassis-dyno rooms that purportedly generated six times the revenues of the dyno itself. At that point, he sold the company for six million dollars in cash.
Over the course of his 27 years of work, Dobeck helped make hot rodding more honest. Performance consumers now expect to know dyno results for speed parts, and dyno tuning and development has become essential for serious racers and hot rodders. Chassis dynos from Mustang, Superflow, and others now provide an alternative to Dynojet, but Dobeck's little bike dyno is the one that started it all.
What's he doing now? Dynojet was recently sold again, terminating Dobeck's non-compete clause, so he's back at it with Dobeck Performance. He reassembled technical talent from the old Dynojet days and has created a handheld gas analyzer (The Sniffer) and a computer interceptor that allows fuel tuning in an EFI car or bike (The Fuel Nanny). He's also looking at a new chassis dyno based on proprietary patented inertial and torque measurement technology. Meanwhile, he's on the road, as always. "Again, I did the routine that works: I put myself right out there in the pits, at the track level, playing around."