MPI injection timing
Turbo Mini Forums

Hi,

I'd like to start a topic dedicated to the injection timing on A-series MPi.

If you know there are existing posts were parts of the discussion have been solved, please put a link. I apologize if I totally ignored existing posts, I've tried to read most of them.

Question: I'd like to know if those of you who calibrated Mini MPi engines could publish here your injection trims.

Idea (yet another): with the usually described Rover timing (injecting while intake valve is open) there are few problems:

- at high loads and RPM there is little time between injector closing and opening (2 to 1, or 3 to 4), injectors are not very precise in this condition. If we don't close the injector in the middle of two injection phases we can face precision problems during the overlap.

- very few existing ECU support this setup.

However these problems can be avoided if injection for cylinders 2 and 3 (the order is 1342 or 2134) starts a long time before the valve opening.
If you look into the port you'll notice that injectors spray in both cylinders. Injecting long before the opening leaves time to fuel to evaporate, it can then be easily transported with the air into the internal cylinder when the valve opens.
Long before can be 360 degrees before the external valve.
This gives 1 injection per revolution, both injectors firing in the same time. So any traditional group fire ECU could be used.

I believe on carb A-series internal cyls run leaner than external. If internal mixture is of better quality due to a good fuel evaporation we could arrange this intrinsic mixture unbalance.

High pressure pulsations in the fuel ramp: many old engines were running in group fire mode with all 4 or 6 big injectors opening together. I don't think opening 2 big injectors would be worse.

BTW, is there a clear explanation of the mixture internal/external unbalance ?

std 998 A+, g295, MD266, RHF4, 109hp @0.8bar/5400rpm

The current version of the siamesed port code for the Megasquirt ECU works on the basis of one squirt per port per revolution. The timing of the squirt can be set and this can be advanced to a table.

The plan is to time a squirt when the outer cylinder inlet valve is open. The next squirt will be 360 degrees later and will sit in the port until the inner cylinder inlet valve opens.

I am currently setting up the instrumentation to test the code on a NA engine. It is hoped that we will collate sufficient information to then apply to a turbo engine.

See my post "Dual Wideband Datalog" for a discussion on the mixture differences between inner and outer cylinders.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

...and look for MPI DATA as there is a powerpoint file i used to log the MPi injection events...

std 998 A+, g295, MD266, RHF4, 109hp @0.8bar/5400rpm

I have read that its bad for hydrocarbons to inject fuel on an open valve.

Unavoidable on siamese ports