EFI Injection Timing

[drl911]

Anyone with EFI set up experiment with the injection timing? My megasquirt MS3Pro was set at 360° as default. This means the end of the squirt is at 360° from TDC, in other words, just as the intake valve is opening. My understanding is you want to spray the back side of the hot intake valve to improve atomization. Research suggests, as rpm goes up, you spray progressively sooner due to the increased speed of the air flow.

I did experiment with the settings and found I could "move" the AFR up and down with different values. I settled on 270° around idle when the AFR max'd out (all the fuel was burning).

Thoughts / comments???

Can anyone share the valve timing curve for 3.2 Carrera head?

Thanks,
Dan

[Tippy]

Deleted

[drl911]

Originally Posted by Tippy

Steve Wong has the standard compression ratio maps on his website you can reference.

I can give you mine tomorrow if you like. This is not dyno tuned, just street.

I'll check out the SW reference information. And I would like to see what you are using as a comparison.

Thanks,
Dan

[Raceboy]

At around 3000rpm there is too little time for the injection event to make any difference regarding timing, therefore just tune what your engine likes best at idle and low loads. There's little use for what others have used, it all comes down to what injectors you use, how you fire them and many more variables like cams, intake etc.

[Tippy]

Originally Posted by Raceboy

At around 3000rpm there is too little time for the injection event to make any difference regarding timing, therefore just tune what your engine likes best at idle and low loads. There's little use for what others have used, it all comes down to what injectors you use, how you fire them and many more variables like cams, intake etc.

That's good info. Kind of like how sequential injection doesn't help much above 3k (arbitrary RPM at best for topic) too.

[Tippy]

My bad, I thought you were looking for ignition timing, not valve timing. Ignore what I said.


Derdeeder....

[Speedfab]

The only place EOIT really has any noticeable effect is at idle, and even that doesn't do a whole lot other than helping "rein in" a cam with a bunch of overlap - specifically with regard to avoiding blowing raw air fuel mixture out the open exhaust valve (Hence why you are "working backward" from END of injection timing rather than choosing a start point). As soon as you pass about 30% duty you will be injecting against a closed valve at some point regardless, so it becomes a moot point. OEMs aren't spraying fuel directly at valves for "atomization", that's a bit of an internet wives' tale. The fact is that fuel spray cleans off valve stem seal oil leakage and controls deposits forming on the back side of the valve head. This has started to become an issue again with the emergence of direct injected gasoline engines.

[dap930]

Dan,

I assume you are running sequential injection. Looking at a 911SC cam (same as Carrera) timing plot in Bruce Anderson's book, the intake valve starts opening around 400* BTDC (TDC being 0*). So, if you want all the fuel injected on a closed valve, then set your end of injection values in the timing table to 400* or something like 420*. But, as engine speed increases, the opportunity (time) to inject all the fuel prior to the intake valve opening is decreasing plus the injector pulse widths get larger. The injection of fuel will likely need to overlap into the intake valve open period. You will need to record a datalog in TS to find out what your max injector pulse width and max duty cycle are when the at WOT and 6000+RPM's. Assuming the injectors are at or less than 80% duty cycle, then you have .01sec/rev @6000RPM's, but there are 2 revs per engine cycle, so .01x2x80% = 16ms. So, for example, @6000RPM there is .0277778ms per degree of crank rotation. Then 16ms/.0277778 = 576* of rotation, leaving only 144* that the injector is not open. So, if the injection started @TDC it would not finish until 144* BTDC. The intake valve closes around 90* BTDC.

[drl911]

Originally Posted by dap930

Dan,

I assume you are running sequential injection. Looking at a 911SC cam (same as Carrera) timing plot in Bruce Anderson's book, the intake valve starts opening around 400* BTDC (TDC being 0*). So, if you want all the fuel injected on a closed valve, then set your end of injection values in the timing table to 400* or something like 420*. But, as engine speed increases, the opportunity (time) to inject all the fuel prior to the intake valve opening is decreasing plus the injector pulse widths get larger. The injection of fuel will likely need to overlap into the intake valve open period. You will need to record a datalog in TS to find out what your max injector pulse width and max duty cycle are when the at WOT and 6000+RPM's. Assuming the injectors are at or less than 80% duty cycle, then you have .01sec/rev @6000RPM's, but there are 2 revs per engine cycle, so .01x2x80% = 16ms. So, for example, @6000RPM there is .0277778ms per degree of crank rotation. Then 16ms/.0277778 = 576* of rotation, leaving only 144* that the injector is not open. So, if the injection started @TDC it would not finish until 144* BTDC. The intake valve closes around 90* BTDC.

Here's the timing chart.
Yes, sequential. I'm going to review the datalog pulse widths soon.

Thanks,
Dan

[drl911]

I created a spreadsheet with the following information / calculations.
Looks like everything can get injected within a closed intake cycle except for when approaching 7000 rpm's (which is rarely).

[l_turn9]

BTW, what software are you using to manage the EFI? I have a BitzRacing based EFI. I have been very happy with it but I seem to be addicted to tweaking the settings. I am always looking for "just a little bit better" as I think of the hundreds/thousands of manhours spent by the factory when they tune a new 911.

[drl911]

Originally Posted by l_turn9

BTW, what software are you using to manage the EFI? I have a BitzRacing based EFI. I have been very happy with it but I seem to be addicted to tweaking the settings. I am always looking for "just a little bit better" as I think of the hundreds/thousands of manhours spent by the factory when they tune a new 911.

I'm using Megasquirt, MS3Pro by DIYautotune.com

[drl911]

Update -

My original post was self misguided as I was reading the angle from TDC instead of backwards as BTDC. Having gone thru the mental exercise this week from the above contributions and creating the spreadsheet, I changed the injection timing table to 410° (BTDC) up thru 2000 rpms and 430° (BTDC) for everything above 2000 rpms. WOW, unexpected improvement!!! I had been perplexed by saw toothed AFR data logs for months which made autotuning an adventure in tail chasing. First drive last night, with this as the only change, resulted in a near flat and stable AFR datalog which allowed the autotune feature of TS to precisely zero in on the target AFR. Cruising surge is completely gone, as well as, improved idle. To think I only stumbled onto this tuning feature by accident while reviewing the megasquirt manual for something else!

[Tippy]

I spent a lot of time trying to figure out sawtooth RPM's and rapid oscillating AFR's. I could not figure which was the cause, and which the effect!

All ended after doing a 30 minute data log and letting MegaLogViewer generate a new fuel map.

Everything cleared up.

[dap930]

Dan,

I have done what you basically did, using 400* - 440* for most of the table, but when I get to 5500+ RPM's my pulse widths get big because of being turbocharged (1.2 bar boost + 11.5AFR). I see 18ms pulse widths at 6000+ RPM's. My 55 lb/hr injectors are a little small. In those areas I have set the end of injection to 180* to 160* to get all the fuel in.

[drl911]

Originally Posted by dap930

Dan,

I have done what you basically did, using 400* - 440* for most of the table, but when I get to 5500+ RPM's my pulse widths get big because of being turbocharged (1.2 bar boost + 11.5AFR). I see 18ms pulse widths at 6000+ RPM's. My 55 lb/hr injectors are a little small. In those areas I have set the end of injection to 180* to 160* to get all the fuel in.

Sounds perfect!

I have 60 lb/hr injectors at only 0.7ish bar of boost so that's why I can get everything injected.

[mikedsilva]

Originally Posted by drl911

Update -

My original post was self misguided as I was reading the angle from TDC instead of backwards as BTDC. Having gone thru the mental exercise this week from the above contributions and creating the spreadsheet, I changed the injection timing table to 410° (BTDC) up thru 2000 rpms and 430° (BTDC) for everything above 2000 rpms. WOW, unexpected improvement!!! I had been perplexed by saw toothed AFR data logs for months which made autotuning an adventure in tail chasing. First drive last night, with this as the only change, resulted in a near flat and stable AFR datalog which allowed the autotune feature of TS to precisely zero in on the target AFR. Cruising surge is completely gone, as well as, improved idle. To think I only stumbled onto this tuning feature by accident while reviewing the megasquirt manual for something else!

I'm at this stage, learning a bit about injection timing. I run a NA 3.0 with itbs and the Rasant Products efi and ignition kit. Not sure what the flow rate of the injectors are as they came with the kit. I sent the car to a local tuner, but I did not take much notice of the injection tables before it went to them. Most of the tables were set at 250 ish degrees.. all differing by a few degrees.. would this have been as per the base map from Rasant?

And would it be a good idea to set my injection timing to the settings you have used? Or is that only for forced induction engines?

[smurfbus]

I tried some changes (from 200 to 450) on idle and as far as I can tell there was little to no difference on my car to AFR. I even switched the base setting from start to end and not much difference. Maybe my cam position sensor is dead and MS3pro has switched to batch mode? Need to log composite to check that.