BMW Bosch EFI Retrofit

rocklord

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I posted a response to a thread in the 144-250 "Small Block" Six Performance Section and thought I'd post it here for you all to mull on.

I've been following a thread on a BMW forum where the DME (Digital Motor Electronics) system found on the M50 24 valve engine has been installed onto the M20 12V engine with success. This has inspired me to research whether that Bosch EFI system found on the 2.5L M50 engine could be retrofitted onto our 200. This system is OBDI utilizing a MAF (mass air flow) sensor with COP (coil on plug) ignition.

The problems I've encountered with this system is the M50 is a 24V engine that utilizes an ignition map that is retarded for our 12V sixes so it would have to be reprogrammed with a more aggressive map, and the engine utilizes both a crank sensor and cam sensor that would have to be retrofitted. Also, the COP ignition units are normally installed on the top of the M50 head between the cams and away from the exhaust manifold heat, but would be adjacent to the exhaust on the M20 engine and our inlines. This may be a concern for longevity of the units so I am watching the vehicles on that forum who have the COPs on the sparkplugs instead of moved to the top of the valve cover as others have who are making room for a turbocharger. I'd prefer to install the COPs on the plugs with heatshields instead of remotely on the valve cover.

I've always thought that a MAF EFI is a very good system for our inlines, and if the above problems can be resolved, the Bosch system would be an economical alternative with the numerous 92 325s and 91-92 525s found in junkyards (sorry, auto recycling facilities). If you think the Bosch system is too small consider that the M50 engine, though only a 2.5L, is rated at 192 hp @ 6000 so it should be adequate. Plus, they are using the system with turbocharging which shows the flexibility of MAF, and some chip reflashing.
 
Given similar displacement and power output, an EFI should be adaptable to a large degree. The optimization will be tough because of the differing power curves, ignition curve requirements, and the obvious volumetric efficiency differences in the two engines.

I guess the bottom line is, it will probably start, idle, and run ok, but it won't give the best performance possible without retuning.
 
It's good thinking overall; there are so many iterations of the Bosch and Magneti Marelli ECUs about, that making one fit is a nice sort of exercise.

So far as reflashing is concerned, all the work I'm familiar with is just substitutional; replacement of the existing map with a full download - it's why people go to aftermarket ECUs for greater controllability.

If there is a south Asian market ECU configuration (by firmware version number) that might be one to check out as it would likely be tempered for poor fuels.

Motorised TB with inbuilt cruise and full diagnostics ability, would be nice touches. For later cars you would definitely need the paired body computer, blindsided for the door locks dash etc, and have the transponder key base permanently bonded to the TX/RX unit.

FWIW I'd buy a new fuel tank and integrate a lock ring on the top - somehow - to utilise an OEM spec fuel delivery unit.
 
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