Spark Timing

 

Spark Timing Myths Debunked


A widely-held myth is that maximum advance always means maximum power. Here’s what’s wrong with this thinking:


The spark plug ignites the mixture and the fire starts burning. The speed of this flame front depends on the mixture, this means how many air and fuel molecules are packed together in the combustion chamber. The closer they are packed together in the same volume, the easier it is for the fire to jump from one set of molecules to the other. The burning speed is also dependent on the air-fuel-ratio. At about 12.5 to 13 air-fuel-ratio the mixture burns fastest. A leaner mixture than that burns slower. A richer mixture also burns slower. That's why the maximum power mixture is at the fastest burn speed. It takes some time for this flame front to consume all the fuel in the combustion chamber. As it burns, the pressure and temperature in the cylinder increases. This pressure peaks at some point after TDC. Many experiments have shown that the optimum position for this pressure peak is about 15 to 20 degrees after TDC. The exact location of the optimum pressure peak is actually independent of engine load or RPM, but dependent on engine geometry.


Typically all the mixture is burned before about 70 deg ATDC. But because the mixture density and AFR in the engine change all the time, the fire has to be ignited just at the right time to get the peak pressure at the optimal point. As the engine speed increases, you need to ignite the mixture in the combustion chamber earlier because there is less time between spark and optimum peak pressure angle. If the mixture density is changed due to for example boost or higher compression ratio, the spark has to be ignited later to hit the same optimal point.


If the mixture is ignited to early, the piston is still moving up towards TDC as the pressure from the burning mixture builds. This has several effects:
The pressure buildup before TDC tries to turn the engine backward, costing power.
The point where the pressure in the cylinder peaks is much closer to TDC, with the result of less mechanical leverage on the crankshaft (less power) and also causes MUCH higher pressure peaks and temperatures, leading to knock.


Many people with aftermarket turbos don't change the spark advance very much, believing that earlier spark creates more power. To combat knock they make the mixture richer. All that happens really then is that the mixture burns slower and therefore hits the peak pressure closer to the right point. This of course reaffirms the belief that the richer mixture creates more power. In reality the flame front speed was adjusted to get the right peak pressure point. The same result (with more power, less emissions and less fuel consumption) could be achieved by leaving the mixture at the leaner optimum and retarding the ignition more instead.


Turbo charging or increasing the compression ratio changes the mixture density (more air and fuel molecules are packed together). This increases the peak pressure and temperature. The pressure and temperature can get so high that the remaining unburned mixture ignites by itself at the hottest part in the combustion chamber. This self-ignition happens explosively and is called 'knock'. All engines knock somewhat. If there is very little unburned mixture remaining when it self-ignites, the explosion of that small amount does not cause any problems because it can't create a large, sharp pressure peak. Igniting the mixture later (retarding) causes the peak pressure to be much lower and cures the knock.


The advances in power of modern engines, despite the lower quality of gasoline today, comes partially from improvements in combustion chamber and spark plug location. Modern engines are optimized so that the flame front has the least distance to travel and consumes the mixture as fast as possible. An already burned mixture can no longer explode and therefore higher compression ratios are possible with lower octane fuel. Some race or high performance engines actually have 2 or three spark plugs to ignite the mixture from multiple points. This is done so that the actual burn time is faster with multiple flame fronts. Again, this is to consume the mixture faster without giving it a chance to self-ignite.


Higher octane fuel is more resistant to self-ignition. It takes a higher temperature and pressure to cause it to burn by itself. That's why race fuels are used for engines with high compression or boost. Lead additives have been used, and are still used to raise the self-ignition threshhold of gasoline, but lead is toxic and therefore no longer used for pump-gas. Of course a blown engine is toxic to your wallet.

Cas

Easily the most critical sensors an ECU relies on are those responsible for providing engine speed and engine position (which cylinder is firing at any time). All of the ECUs calculations for fuel and timing are based on these inputs so they are essential for the ECU to be able to do its job.

There are almost as many trigger systems available as there are engines, and every manufacturer has their own ideas on what works best. In the aftermarket our options are a little more varied though. In the perfect world we want to take an engine speed input directly from the crankshaft as pictured here. In this case a 24 tooth trigger disc is mounted to the back of the crankshaft and monitored by a Hall effect sensor.

There is no magic number for the correct number of teeth on these trigger wheels, and the correct choice will depend on your particular ECU and application - A higher tooth count gives more information to the ECU and this can improve resolution and timing accuracy (this is particularly noticeable at idle or low rpm). The trade off though is that at very high rpm the high tooth count can become a problem for some ECUs, resulting in the ECU getting confused about engine speed and this can cause ignition timing inaccuracies or misfires.

The engine speed input is only part of the puzzle though. For the ECU to be able to decide which cylinder is firing at any time, it also needs an engine position or synchronisation input. Since the crankshaft makes two full revolutions (720 degrees) for a single engine cycle, the synchronisation input needs to occur once every two crankshaft revolutions. That sounds complicated but since the camshafts turn at half engine speed, this is the perfect place to take the synchronisation input from.

An engine position input is essential for true sequential injection and direct spark control so should be high on your priority list if you want the most out of a modern ECU.

Haltech Platinum Sprint 500

Engine Suitability:

• 1 to 8 Cylinder engines

• Normally Aspirated or forced induction

• Load sensing by throttle position or manifold pressure (MAP)

• Sequential, semi-sequential, batch or multi-point injection patterns

• Distributor ignition systems or multi-coil systems



Trigger Types:

• Hall Effect

• Optical

• Inductive Magnetic Reluctor



Trigger Patterns:

• Single Pulse per cylinder

• Multi-tooth

• Bosch Motronic

• Ford

• GM

• Honda

• Mazda

• Mitsubishi

• Nissan Optical

• Subaru

• Toyota

• Volkswagen



Features:

• Windows 2000, XP, Vista compatible software

• Real time programming, instant hesitation free adjustment while engine is running

• Fully user definable 16 x 16 mapping

• Tuning via Volumetric Efficiency (VE), Injection time

• Selectable onboard internal MAP sensor rated to 150kPa (up to 1.5 Bar or 22psi boost)

• USB and CAN Communication Port

• Custom sensor calibaration allows for most factory sensors to be used

• 2 x User programmable outputs



ECU Fixed Outputs:

• 4 x Fuel Injector outputs (for high impedance injectors only (ie: above 8Ω)

• 4 x Ignition outputs

• Tacho

• Thermo Fan

• Fuel Pump



ECU Programmable Outputs:

• 2 x Programmable Outputs



ECU Inputs:

• Air Temperature

• Aux Rev Limiter

• Coolant Temperature

• Manifold Absoloute Pressure

• Roadspeed

• Throttle Position

• O2 Sensor (Narrowband or Wideband)



Functions:

• CAN Communication

• O2 Control

• Over Boost

• Gear Setup

• Decel Cut

• Transient Throttle Enhance

• Rev Limiter



Correction Tables: Fuel / Ignition:

• Air Temp Correction

• Barometric Correction

• Coolant Temperature Correction

• Injector Dead Time

• Map Correction

• Post Start

• Prime Pulse

• Wide Open Throttle

• Zero Throttle



Miscellaneous:

• Tune can be password protected in software

• Small and compact design

• Rugged anodized aluminum casing



Power Requirements:

Source: 8.6 to 16.5 Volts DC

Consumption: 360mA @ 12Volts DC



Physical Dimensions:

ECU Dimensions Length: 134mm (154mm with MAP nipple)

Width: 64mm Height: 28mm Weight: 195g (0.43 lb)



The Platinum Sprint 500 Kit includes:

Platinum Sprint 500 ECU,Platinum Sprint 500 Flying Loom, USB Cable, Programming Software CD,

Quick Start Guide, Instruction Manual (on CD), Haltech Sticker

Power or Torque

Power or Torque - Which do you think is most important?



It's a simple question, but the terms power and torque are two of the most misunderstood and misused in our industry. When it comes to tuning, often we hear the request ‘I want maximum torque’, or ‘I want a tune for maximum power’, suggesting that the two terms are mutually exclusive. The reality is that torque and power are inextricably linked by a simple formula: Power (HP) = Torque (lbft) x RPM ÷ 5252. This formula means that provided there is RPM, we can’t have torque without power.

When we tune a car on a dyno, the dyno measures the torque being produced by the engine and then the power is calculated from the torque and the rpm at which the torque was produced. If we look at a dyno sheet showing torque (in lbft) and power (in hp), we will see that the two lines always cross at exactly 5252 rpm - At this point the RPM cancels out the constant of 5252 in the equation, and torque is equal to power. If we understand the relationship, it should be clear that torque and power go hand in hand, and if we optimise the torque produced at each rpm, we must also achieve maximum power at each rpm - We can’t have one without the other.

EFI tuning isn’t magic, and the engine’s ability to produce torque is an aspect of it’s mechanical design, not how good we are on the laptop. If the engine is provided the correct amount of fuel and ignition advance, it will make the torque it was designed to. Changing the actual shape of the torque curve, or where in the rev range peak torque is achieved requires mechanical changes to be made to the engine (cam timing for example).