Ta lambertius
can you explain the reasonings behind needing to go standalone management for my stroker? I'm good with the mechanical side of it all but I'm a complete novice when it comes to electronics/management etc
An ECU at its simplest uses a single sensor to determine some environmental factors for an engine, which are then used to identify information on a lookup table to provide information on ignition timing and fuel. This information is referred to as a map, which is where you get expressions like a fuel map or timing map from.
http://en.wikipedia.org/wiki/Engine_control_unitAt the most basic, the single sensor is usually a throttle position sensor because the type of sensor used is very reliable. However, when you only use one sensor, other aspects of your environment can change such as air temperature, density and humidity which will affect the accuracy of fuel and timing maps.
In order to improve engine performance and efficiency you can relay more information from more sensors. If you know the temperature of the air, and the velocity of the air entering the engine (via the MAF) you can work out the density of the air. This allows you to accurately gauge the amount of fuel and timing needed to optimise performance. Further, if you monitor the exhaust mix you can determine the efficiency of the burn as well as using knock-sensors to identify the quality of the fuel. A system that implements all of this information is running in 'closed-loop' since it is actively monitoring all inputs and outputs and adjusting the system on the fly.
http://en.wikipedia.org/wiki/Open-loop_controllerhttp://en.wikipedia.org/wiki/PID_controllerMost engines run by referring to maps, including MIMO (multi-input multi-output) systems instead of 'true' closed-loop - this particular point is why you will need to change your computer. Our cars, despite taking in a huge array of information, don't actually dynamically adjust like in a real closed-loop system. They do adjust some items but most of it is gained via lookup.
Engineers will test engines exhaustively for months and create tables that have every possible condition they can think of, plus more. All the sensors will monitor what is happening and then that information will be found on a table, and the engine will run designated timing and fuel. By monitoring the AFRs you can effectively determine if your fueling is correct, and by monitoring engine knock you can determine if your timing is correct. If it is incorrect, the computer makes a note that that map it referred to was incorrect and moves onto the next most likely option. This isn't true closed-loop, but the loop is effectively closed
provided the information required is already in the table. This should be how the DME 1.7 operates.
With the DME 5.2 it is slightly better than that. It is able to write its own maps rather than referring to an endless, and slow, supply of pre-written information. However it still relies on a 'safe' operating reference point, so that it won't blow the engine up. The more your drive it, the more 'refined' the reference map becomes as the map adjusts to local conditions and driving patterns.
The reason my car still works with the stock ECU and is making reasonable power gains is that I haven't changed the internal dynamics of the engine - it still has the same compression and cams, so the 'reference' point is still the same, just more conservative than it would've been on the stock setup. The changes made really only affect one sensor, and that is the MAF. The engine knows there is more air going in, and monitors the AFRs to confirm what is going on, so it all works.
For the same reason the kit should work on any stock M42 engine with its stock computer. BMW engineers would've programed more than 20% variance for MAF just based on the potential for air density changes in weather and altitude, so even on a lookup table the stock computer should just work but with a higher probability of not being perfect.
The problem with what you're wanting to do is that all of the default expectations that your computer has will be wrong so it won't be able to find a correct map. The computer has certain expectations and limitations it is working with which dictake how fuel and timing are controlled. For example, a longer cam duration would change
when fuel can be injected, not just how much. Higher compression would alter the ignition timing from stock for the same mass flow rate. By getting a custom computer tuned specifically to your engine dynamics you can significantly increase performance. With everything stock, gains can be made but on a sophisticated NA engine they are very small unless something is actually wrong.
So the
tl;dr version:
As long as you don't change the internal engine dynamics, the BMW engineers should've written enough information for NA mods to work cost-effectively.
