Semi direct injection conventional injector timing?

[yellow-fever]

Anyone ever mess with injector timing? I have a 1000 2 stroke Semi direct injection. The stock ECU has normal conventional injectors in the transfer ports so when the piston is at bottom dead center it injects fuel directly on top of the piston like a DI engine but at BDC where the piston top is open to the transfers and the injectors are not under high cylinder pressures, AKA the "Semi" part of 1000SDI semi direct injection. If you inject fuel at the wrong time it washes the oil off the back side of the piston and causes scuffing from lack of oil. Any tips on how to make sure the injectors squirt at bottom dead center? Not sure if megasquirt can do this without squirting at TDC and BDC? I absolutely need to be sure it's not washing the oil off the piston skirts on the back side before I try this. I may just fit throttle bodies with injectors and chicken out! It's a twin with 180 firing. I need 1 squirt in cyl 1 at 180 and 1 squirt in cyl 2 at the 0/360 and it would work. The MSQ attached is not actually running anything and it's just logging and experimenting with at this point.

[hybrid]

There is (or was) a timed injection setting for the MS2, but people were having issues with it under certain conditions.
Try searching for timed injection either here or in the manuals.

[racingmini_mtl]

No need for the obsolete timed injection setting. The sequential injection setting should work fine on a 2 cylinder 2-stroke engine using the 2 standard injector channels. You simply need to set the injector 1 timing and the injector 2 will be 180 degrees later so that it is at the same angle with respect to its TDC.

One thing you need to check though is the fuel transit time. In a normal port injection setup, the fuel takes some time to travel from the injector tip to the cylinder so you need to fire the injector earlier than the event you want to sync to (opening or closing of valves for example). In this setup, I have no idea how and where the injectors are located with respect to the cylinder so I can't offer a suggestion. Also, this transit time is usually dependent on load and RPM so you would need to use the injection timing table and not just a single timing value.

Also, you can use timing with respect to the middle of the pulse, the beginning of the pulse or end of the pulse depending on how you want the timing to be affected when the injection pulse width varies.

Jean

[racingmini_mtl]

One thing I should add is that you will need to have injectors large enough to only require a small duty cycle (probably less than 50% depending on your injection window). If you have injectors that are smaller than that, no matter which injection timing you select you will still get fuel when you don't want it.

So larger injectors will make timing less critical because you will have more margin on where in the cycle the injection pulse can be located. But with larger injectors, it will be trickier to tune at low RPM and low load (idle).

Jean

[hybrid]

You'd think the same restrictions would have been a problem for the factory ECU too since it's literally a physical issue with regards to port timing.
So if they had to work within the same constraints, the stock injectors would be pretty well sized.

[racingmini_mtl]

You'd think the same restrictions would have been a problem for the factory ECU too since it's literally a physical issue with regards to port timing.
So if they had to work within the same constraints, the stock injectors would be pretty well sized.

Yes as long as there has not been any modifications and that he's using the stock injectors.

Jean

[yellow-fever]

I found the timing tables and the beginning, middle and end settings but without a way to log stock injector timing, I'm chicken! I'm going to mount 2 injectors in the throttle bodies and just let the stock SDI system do its thing with the 4 in the transfer ports. I'll use the 2 extra just to add fuel when I mount the turbo. The 1000sdI uses 2 large and 2 small conventional injectors in the transfer ports. The 600sdi used 4 small conventional in the transfer ports. If I get brave, I'll put 4 small in the transfers like the 600sdi and I'll add the needed fuel back with the Microsquirt at the throttle bodies to see how it reacts before adding the turbo in the mix. If I could just log injector and ignition timing................What kind of equipment would one need to datalog things like that from a stock ECU?

[hybrid]

You could probably use just a two channel scope.
Put one channel on the factory injector, and the other channel on the MS injector output without any fuel to that injector. You could just adjust the MS injector timing until it matched the factory timing on the scope.
It would be interesting to see if the factory fired the injector earlier and earlier based on increasing RPM, or if it was just a set degrees BTDC.

[yellow-fever]

Great idea! I have a dual channel scope at work I can use. I can take a few logs with it a different RPM ranges comparing the stock and Mcrosquirt signals, one on top of the other in the same graph and tweak accordingly so they match and that is my timing map. I'm going to try it to create a stock spark map as well.
Thanks for all the replies!