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Reanimotion Reanimotion is offline
umop apisdn
Join Date: Jun 2014
Location: Brisbane, Australia
Posts: 557
Originally Posted by RarlyL8 View Post
We'll fiddle with our screwdrivers and you can go play with your laptop.
Or you can do both on the one vehicle

I'm one of the fence sitters when it comes to EFI conversion, when chasing power and performance I've always retrofitted a larger capacity driveline in a smaller vehicle.
So for me, more power would be a Panamera turbo swap (or that 4wd thing) into the 928, what I am chasing is NVH and drivability. Updating the old beast with modern tech where applicable.

So for arguments sake, assume that in general, budget oriented EFI retrofits are not taken to a high level of tune under all possible operating conditions, as many never see a dyno or a professional tuner.
And also assume that a majority of factory systems including CIS are most likely in poor condition prior to the move to aftermarket EFI.

Also considering the advancements in injector and control technology over the last decade or so. And the theory that delivery method is less important than accuracy when discussing an engines Fuel/Air/Spark requirements.
A highly calibrated twitching monkey with a bucket of fuel and a hose, if delivered at the right location and the right quantity, could in theory be your fuel system. (A similar and suitably insulated monkey, also calibrated, with a coil and a switch could handle ignition duties)

Are we certain any of the available data represents either system fairly?

My nutty little project was undertaken purely because of that uncertainty.
- I'm not concerned with originality, but changes must blend in functionally and visually.
- I am wary of change for the sake of it - the changes must have a verifiable benefit, and be of the same or better quality in form and function.
- I knew and could verify that the CIS on the vehicle was in good condition and operating to spec before any changes.
- I was dubious as to the ability to replicate the base line tune in less than a year. i.e cold and hot, summer and winter, city and highway etc. etc.
- CIS had some failings and EFI had some advantages, so could the positives from both be merged eliminating the negatives.

So my questions to the group
I am curious though as to the throttle response comments.
A prior post mentions correctly that mapped timing will see improvements over mechanical advance. I've also seen and heard numerous comments over time that CIS has better atomisation due to the pressure levels and that CIS also has better throttle response over standard EFI. Bosch also state in the technical instruction manual that CIS was designed for performance, although the comparison system could only be L/LH-Jetronic and possibly early Motronic.
Ignoring ignition and data logging as electronic obviously trumps mechanical.
Is there actually a functional limitation to CIS or are the identifiable issues related to the lack of control rather than capacity.
For a high HP installation if we imagine CIS was able to supply the correct amount of fuel under all conditions is there anything EFI would still bring to the table as an advantage.
Is there any truth to the CIS = Performance comment from Bosch?
1981 928S 4.7 ROW with KE3-Jetronic
"Be the man your dog thinks you are."

Last edited by Reanimotion; 10-19-2014 at 10:43 PM..
Old 10-19-2014, 10:35 PM
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