Fuel Injection Performance Upgrades
Mike, you have certainly touched on some very interesting points here. It is clear that you have put quite some thought into the subject. I too have been researching how to improve the stock fuel injected engine.
Clearly one of the first things that needs to be done to the engine (before modifying the fuel injection itself) is to raise the compression and change the cam shaft: both of which severely limit the performance of the motor. I believe that this should be done first as any subsequent modifications will depend on the characteristics of the engine. As you mention, adding a higher lift cam doesn't seem to work too well with the standard Bosch system at idle, so this is one thing which needs to be addressed in the FI modifications.
I would also note that an excellent source of information on the L-Jetronic and later Bosch systems is "
Bosch Fuel Injection & Engine Management" by Charles o. Probst.
There are a number of good choices in aftermarket EMSs, of which Megasquirt is certainly the most popular, presumably primarily because of its price. When Megasquirt entered the market there were very few EMSs offered, and those that were available were rather pricey. Megasquirt literally brought programmable EMSs to the masses. There are quite a few more options now, so it's much easier to find something that meets your specific goals. FWIW, the Autronic units look to be very interesting, although they are significantly more expensive than Megasquirt.
Motronic
I would like to investigate the conversion of an X1/9 from L-Jetronic to Motronic. It seems that this modification has been done by several BMW owners (although they are lucky in that later model BMWs used Motronic). In the case of the X we would need to add a RPM and TDC sensor on the front of the crank shaft and swap the distributor with one without any form of mechanical or vacuum advance. The advantage of this swap is that it is relatively easy to set up, parts are cheap and you end up with control of both injection and timing. As the Motronics are digital, the timing and injection maps can be modified.
Modified L-Jetronic
I'd also note that there are
a couple of mods that you can perform on the standard L-Jetonic system to provide some extra performance (within limits). The most popular is to increase the resistance from the coolant sensor which tricks the "computer" (it isn't really a computer in L Jetronic, but let's call it that for now) into thinking the car is cooler and therefore supplying more fuel. A similar mod can be done on the air temp sensor (mounted in the AFM). I don't believe that either mod offers better performance in all circumstances and therefore I have made a console which allows me to "dial in" increased resistance to both inputs (as well as being able to switch in the full throttle switch before full throttle). Again, these mods can't really be considered a viable long term solution, but they do provide an interesting lesson in how the L-Jetronic responds to modified inputs. Note that significant mixture enrichment can be detrimental after a certain point as the Lamda sensor will not be able to compensate and the catalytic converter can go past its operating temperature range. There is also an AFM mod that you can do, as documented here:
http://www.hiperformancestore.com/Ljetronic.htm
I'm also running a fully programmable ignition system with no mechanical or vacuum advance in the distributor (timing curve depends on RPM and manifold air pressure, measured by a MAP sensor).
Just to clarify, the X1/9 EFI (Bosch L-Jetronics) uses an airflow meter (AFM), not a mass airflow meter (MAF). AFM is old technology, but MAF is used on virtually every injected car made today, including most of the top line exotics. IMO it is an excellent means of measuring airflow, although most DIYers seem to use MAP (Manifold Absolute Pressure).
Some Xwebers are running 40/80 or wilder cams with the stock AFM, although most of them will admit it's not ideal. AFM uses a spring loaded plate to measure airflow. That plate pulsates with the intake reversion caused by a high-overlap cam, which presents a number of problems at lower RPM.
Are you sure that it is the AFM which is the problem here and not other characteristics of the standard L-Jetronic configuration? I'm planning to install a Euro 1500 cam in my FI X and will be researching how to negate any negative characteristics of this configuration.
On top of that, the AFM literally presents a "barn door" to the column of air moving through the intake tract. This interruption of the intake charge inertia has a large detrimental effect on power output, particularly torque-- the engine is not only being strangled, but much of the "inertial supercharging" effect of intake resonances is negated. IMO, that is the single biggest drawback of the stock injection system.
This is a common criticism of the AFM system (and clearly a hot wire system is superior in every way) although I have also read that the effect is not as great as many are lead to believe.
However, you could either replace the AFM with a MAF (my preferred solution) or remove it and use a MAP or other means of measuring airflow, but still retain the rest of the original components (other than perhaps injectors), and integrate that with the aftermarket EMS of your choice.
If you replaced the AFM, EMS and injectors, you wouldn't have much of the "original components" left to retain! :wink2: BTW, using a MAP sensor is even worse than an AFM (according to Bosch anyway who moved away from this technique after the D Jetronic system used in the early 70's). Manifold air pressure is dependant on a number of corrections for temperature, altitude, etc.
This would remove the intake obstruction presented by the AFM, which would result in instant power gains all by itself. It would also solve many of the problems presented by a more aggressive camshaft, at least with regard to the EMS.
Agreed, but I think that the whole problem needs to be addressed together: air density measurement, injector timing and ignition timing. I'm thinking that starting with a pre-configured Motronic might be an easier starting point than Megasquirt where you basically start from scratch.
My own plan is to do just that initially, in order to create a good, simple base mechanical installation so we can test out and become familiar with the particular EMS we'll be using. Once I'm comfortable with how it all works I hope to move to an individual throttle body (ITB) arrangement, both for the extra power and for the sound. I intend to use a MAF for both arrangements because I prefer the advantages it offers.
I have no data to support the following statement, so take it with a rather large grain of salt, but I suspect that a well tuned aftermarket EMS using MAF and running through a nicely ported, port matched, and polished stock plenum/runners would probably yield roughly as much power as the average DCNF setup.
Good luck, I'm looking at doing something similar (i.e. a well tuned fuel injected car which still complies with the relatively strict rules we have here in Germany concerning modifications and emissions). I think that we differ slightly in the implementation approach, but the goals certainly seem similar. It would be interesting to swap notes when the projects are complete.
Cheers,
Dom.
