[The Capri's engine bay with the M60B40 up and running]
I chose to use a Microsquirt ECU which is a smaller encapsulation of Grippo & Bowling's Megasquirt system and appears to function well. It's not as advanced as the original Bosch unit so in some ways it's a retrograde step, but on the plus side it is fully programmable.
There seems to be some debate as to whether the BMW's Bosch DME ECUs from 1992 onwards are stand alone or not (i.e. can function on a few +12v inputs outside of the vehicle's other computer systems). According to the wiring diagrams i got hold of, they require inputs from the dashboard, immobiliser, and autobox computer. I've been told that if the immobiliser is disabled by a specialist then the ECU can function outside the car. But i didn't know this at the time i started the conversion so i threw all the original Bosch ECU stuff away.
If it can be made to work outside of it's original home then using the BMW's ECU would save a lot of hassle & expense, because you have to spend a fair few pennies to get an aftermarket ECU that is anywhere near as powerful as the original Bosch unit.
I found this pic of an M60 installed in a Granada on the web (German/dutch conversion i think) that appears to use all the standard engine loom and airflow meter (i presume it's using the Bosch ECU as well) - so it must be possible. But i haven't been able to find out any more about the conversion.
Another option could (?) be fitting an ignition-only computer (Megajolt or similar) and 2 sets of bike carbs. But this might be a headache to setup and balance all eight carbs. Given the airflow requirements of the V8 you'd probably want the biggest bike carbs you could get hold of and get them re-jetted with the help of a wideband Lambda sensor to check the fuelling throughout the rev range. And you'd have to fabricate a set of custom inlet manifolds which looks something like this on the Rover V8:
[Photo courtesy of Jonathon Ellison's V8 Chevette, fabrication by Bogg Brothers]
I don't like all the extra complexity introduced by having to use an aftermarket ECU but with no distributer position it's not really feasible to revert to the old clockwork way of doing things. For me it meant swotting-up on a whole load of new electronic systems and terminology that seemed like gobbledeegook to me. But you've got to move with the times i guess.
An advantage of a programmable ECU is that if in the future you decide to fit turbos, a supercharger, or individual throttle bodies (ITBs), then the ECU can be reprogrammed accordingly on a rolling road. And with a properly mapped ECU you should be able to get some reasonable mpg figures on the motorway. As the engine was originally designed for complete digital management it would seem a retrograde move to junk the EFI for carbs.
In comparison to old 2-valve V8 designs these new multivalve V8s really do rev and if you added a carefully designed exhaust and ITBs then i suspect they would carry-on revving quite a bit further than 6500rpm limit on the standard ECU. If you were feeling flash you could also splash out on reground cams which with the right head-work, exhaust design and mapping could certainly get the M60 up to 90bhp/litre.
[photo courtesy of VacMotorsports.com]
This is the microsquirt ECU that i used, available from www.trigger-wheels.com in the UK.
It's quite a small encapsulation, slightly larger than a pack of cards. The wiring did take quite a lot of concentration and effort, but there was a huge amount of satisfaction when the engine actually burst into life. Apart from the fiddle of fitting a new trigger wheel and the EDIS-8 ignition module (see ignition page) all the other existing BMW sensors can be used - throttle position sensor, Inlet air temp sensor, water temp sensor, idle control valve and crank sensor.
The Microsquirt and MS2 Megasquirt units can't provide sequential injection, they run 2 injection outputs with up to 6 high impedance injectors on each output. How detrimental this is to performance i'm not sure. Continuous-spray mechanical injection like Bosch's K-jet system seemed to perform well in terms of outright power and so do carbs if they're big enough so i like to think that sequential injection is more to do with avoiding fuel fallout (droplets forming on the port walls) for increased economy and so-on. Sequential fuelling and ignition also gives the ability to trim the fuel and ignition specifically for each cylinder which allows manufacturers to compensate for things like central cylinders running slightly hotter.
For the oxygen sensors, i didn't have the BMW Lambda sensors available to me, so i used an Innovate LC-1 Wideband controller and sensor. The advantage of the LC-1 or similar wideband is that you can run a dashboard-mounted mixture display to allow you to keep an eye on the fuelling at all times. Also you can run feedback loops in the programmable ECU to adjust the mixture to a set fuel ratio table stored in the ECU when the engine is at cruise. And the most powerful feature is that you can log your A/F ratios whilst out driving in various rpm/load conditions and then run the log through comparision software which then suggest changes to your fuel map. It seems like the technology for a self-mapping ECU is not far away.
The inlet air temperature (IAT) and water temperature sensors need to be callibrated to the ECU. If the resistance values for the sensors are unknown (i.e. not available free anywhere on the web) then they can be calculated by taking resistance readings at different temperatures, normally -10 C (in the freezer), 32 C (in the armpit) and 95 C (in the kettle). The software for the ECU (easytherm) can then interpolate the rest of the values.
The BMW idle valve is a 3-wire PWM type, but can be controlled effectively from a simple ECU like the Microsquirt by fitting a large grounded resistor on the closing side of the coil. This acts as an electromagnetic spring, enabling the valve to be controlled by one wire from the ECU. Finding the correct idle settings in relation to coolant temperature is a trial and error process and often needs recorrecting when other engine variables are altered (ignition timing & fuel mapping).
All the information for wiring-in the Microsquirt system is available at www.microsquirt.info
For a programmable ECU a new MAP sensor (Manifold Absolute Pressure) is needed. The BMW system uses a heated bridge airflow meter (hotwire meter) which isn't easily compatible with aftermarket ECU systems. A MAP sensor is far simpler, and it means there is no restriction whatsoever in the inlet tract.
These are available in 1,2 or 3 bar depending on whether you need to cater for forced induction. A 2nd hand MAP sensor from a GM car (these are fairly easy to wire in) can be bought very cheaply 2nd hand. The one i am using is from a Saab of some kind:
