M70: Original injectors vs modern 4 hole "blue" -- different flow rate

[paulmer]

Hi all,

I like having spares (plus curious what condition my old injectors were really in) so I had them tested against the new 4 hole injectors. Here is the report:
Flow report.jpg

Feedback from Mr. Injector:

They are not a perfect match, but they may work okay. You would need to try them. They flow at 20cc/min higher rate than the original injectors which is 12.5% higher than stock. The spray pattern is a split spray which is designed for a cylinder head with two intake valves per cylinder. If the 750il has one intake valve per cylinder the spray may hit the walls of the intake manifold instead of the bottom of the intake valve.

I understand from shogun, wokke and others the different spray pattern/hole design has no material impact due to the low compression, single valve, combustion chamber design, etc on M70. However, does the different flow rate have any impact? Will this harm my fuel economy?

I seem to recall that DME can compensate for different flow rate, right?

[shogun]

as far as I understand it: Our old stone age DMEs are very limited, they have the original selected fuel injectors flow rate in the basic program and the DME calculates based on that, the changes one can make on the DME chip is the ignition timing and the time of injection, the O2 sensors will react if there is too much fuel injected, but the adjustment is also limited.
The ignition point and injection duration are jointly processed by the ECU so that the best moment for ignition and fuelling are determined for every operating condition. The injection function of the Motronic system is based on the even older 'L' jetronic system, although a number of refinements have improved operation.
Here the description of M1.1 and M1.3, M1.2 and M1.7 are basically the same function http://www.meeknet.co.uk/E32/DME_1.1_1.3.pdf
I personally would stick with the original flow rate for the M70.

[paulmer]

Interesting shogun. I did some research on the E31 forum -- apparently many 850 guys (ie Wolf) are even running 19 LBS on NA M70 engines and it runs well. I got these 17.1# injectors from dragon850, so I trust that it will run well with them, was just curious

[whiteghost1]

I’m not sure the spray pattern is as important on an older fuel injection system such as ours. Reason I say this is these motors are batch fire, so the fuel is going to be sitting on the back of the intake valves for some time (relatively speaking). I point to the fact that the e32 is an OBD 1 system, vs the OBD 2 system used after 1995 which is much more precise. So really, is the atomization of the fuel from the injector that important, when the fuel consumed is not going to be in an atomized state....majority of the time?

I forgot what the stock M70 injectors flow at, but I believe it’s around the 15 lb/hr mark from memory. I could see there being enough adaptability in the DME with the 17 lb’ers, but 19lb injectors might be pushing it without retuning the fuel map accordingly. For sure with either upsized injector, you’ll be running richer at WOT, when it’s in open loop.

[shogun]

same opinion, the fuel injectors on this old engines are far away in the intakes, good to see here https://www.7-forum.com/bilder/model...ung-b_jpg.html
and here the head port cutaway/ geometries http://www.mwrench.com/Whitepapers/B...Geometries.wmv