This is probably more an ECU related question but seeing as it's not a topic that's specific to one make of ECU I've chosen to put this here instead but feel free to move it to a more suitable forum if needed.

Now that I have the mechanical side of things stable on Black Budgie I've turned my attention towards devoting some serious time getting the absolute most out of the engine by means of getting the tune as close to perfect as possible. So far just in the fuel map alone I've managed to improve throttle response, increase overall power across the whole RPM range and reduce fuel usage by a very noticeable amount.

But one area of ECU tuning that seems to have the least amount documented about it but can greatly affect power, emissions and efficiency is Fuel Injection timing (or firing angle) or the exact point in the combustion cycle that the injector fires the fuel into the cylinder. Just a change of a few degrees can have a significant effect on the amount of fuel needed to achieve a desired Air/Fuel Ratio (AFR).

My understanding is that you need to adjust the firing angle until the richest AFR possible is obtained across all load points, because that would be where the most amount of fuel possible is entering the cylinder and provided you can give it enough air to suit then that would be the way to extract the most amount of power possible. Once this is done then adjust the fuel map to achieve the desired AFR across the RPM range. Obviously this would be a bloody slow and time consuming task especially if there are variable cam timings to deal with, and even more so if using a map with a lot of load points.

So my questions (and requests) are:

Is the method I mentioned above the correct (and most efficient way) to do this, or is there a quicker and more effective way?

Is there a direct (or even rough) correlation between Injection Timing and power for a given RPM range and load point? Obviously things like valve (and port) sizes and cam timing and even ignition timing will all affect the optimal injection timing needed to achieve an optimal result.

Would those people with programmable ECU's who have the ability to access the tuning maps please send me a copy (to rubberbudgie@hotmail.com) of their fuel injection timing maps & variable cam timing maps (in either CSV format or even just a screenshot) and a quick description of the engine internals (especially cam settings if possible) and who tuned the ECU so I can try and work out a pattern as to which is the best way to achieve the optimal results for various engine configurations.

Thanks heaps

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fuel injection timing has more to do with inlet runner lengths and injector position as far as i know.

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On the power FC the injector timing is defined as injector lag correction.

I wouldn't have thought it would affect the afr's largely unless the the base timings were way out & the injector was spraying into the valve pocket on to the back of the valve just prior to it opening (i.e too far advanced).

My understanding is the further the injector is from the valve pocket/port or the longer it takes an injector to open, the larger the lag number in ms.

I ran a 13b turbo (on a microtech ecu) with 4 extra 800cc injectors (secondary bank) firing down it's long runners from the top of the plenum chamber, this introduced a long delay from when the injector fired to when the fuel reached the inlet port.

On boost the delay we found that worked was 40ms...how that would translate into degrees of inlet timing or injector advance/retard I have no idea!

The delay number fired the injector earlier to get the fuel to the port at the start of the induction cycle....So it's not really a delay as it's firing the injector earlier.

How this translates to Motec I have no idea.....

I suspect that there won't be any massive gains found though.

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From what I've seen in the past injector timing has the biggest effect on fuel economy/emissions at lower loads and about a 5% gain at the most in power at higher loads. But it is very time consuming to get that last 5%.

You are right in that you want to adjust injector timing to give the richest lambda at each cell, as this indicates the engine is more efficient and burning more of the available air in the cylinder with the same amount of fuel injected.

How do you have the table setup currently? I assume it is a end of injection 2D table on RPM. Have you considered possibly using a 3D table with RPM and cam advance. That way you could adjust the injector timing to follow the inlet cam at various RPMs.

There is a good explanation on injector timing on the motec forum.
Link

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Yes I have read that link at least 100 times over the past 6 months or so just in case I misread something or didn't quite understand the concept

And yeah you are dead right in that the majority of the gains to be made are in the lower RPM range. I've just started a new map with injection timing starting at 450 degrees (as per the Motec guide and the mention about Subarus with the TGV's deleted) and going up in 5 degree amounts per 500 RPM and have already noticed that between the 1000 - 2500 RPM range it's needing a LOT more fuel to achieve good AFR's and throttle response and overall feel of the car is much more alert and responsive. After that it seems to die off although I haven't really tuned much past the 2500 RPM range so can't say for sure.

Your idea about the 3D table sounds like an awesome idea in theory but as I'm still learning Motecs it might take a bit of doing to get right but as with anything I'm more than happy to give it a go.

I'm guessing there is a more of a direct link between injection timing and CAM advance that I would have first thought seeing as you are suggesting to put them on the same table? I'll give the 3D table a go later on tonight and let you know how I go with it

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I wish I could adjust injector timing, but with romraider and the stock ECU it’s not available to change. If the Subaru ECU works anything like the EVOs then they fix the start point of the injector to a particular tooth on the crank.

But my understanding of injector timing is it gives you the adjustability to inject fuel onto a closed intake valve or an open intake valve. I have read conflicting information on which is better. Some say at low rpm and load to inject only when the valve is open and others say to always inject onto a closed intake valve. That is why I suggested you use a 3D table, to keep the relationship consistent.

I find it easier if I can visualise what these numbers mean and my understanding is a value of 360 is to stop the fuel injector at TDC when the intake valve begins to open and 400 would be 40 degrees BTDC, likewise 320 would be 40 degrees ATDC.

Here is a link to a diagram that I found useful.

So as Motec suggest 450 at idle and an additional 5 for ever 500 rpm after it would indicate they prefer to inject fuel onto a closed intake valve and letting the fuel pool up. This may not give you the best atomisation as the fuel will condense on the valve and could also get partially blown straight out the exhaust due to intake and exhaust valve overlap, which would agree with what you were saying about it needing a lot more fuel to reach desired AFRs. But if the engine feels happier that way then it sounds good enough to me.

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