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Ethanol Fuel Blend Worksheet

Flex Fuel Tuning

Discussion and questions related to the course Flex Fuel Tuning

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Just going through the supplied spreadsheet for this part of the course, and noticed that you have;

Initial Injector Scaling Value = 500 cc/min (input)

Fuel Volume Required = 142% (caluclated)

New injector Scaling value = (500/142% = 500/1.42 =) 352 cc/min

Should this be

500*142% = 710cc/min

to account for the extra volume?

Apologies if this has been bought up previously, I couldn't find the appropriate thread.

It is working backwards - the smaller the size of injectors,the longer ECU holds them open in order to inject more volume of fuel. If you will increase injectors size to 710cc ECU will open them for less time than required in reality and that will result in very lean air/fuel mixture...

Thanks for the reply, but I don't follow any of that logic...

The logic is very simple - you need to inject 1.3 times bigger volume of fuel during the same engine cycle time. How do you do that?

You mention the smaller injector being able to inject more fuel because the ECU is holding it open longer, but the larger injector not injecting enough fuel, as if there are two cases - you can adjust the pulse width with the small injector, but not the larger injector.

The way I see the calculations in the spreadsheet is if you have a constant pulse width and fuel pressure, the only way to achieve the required volume of fuel is to increase the injector size, but the calculated amount.

To answer your question though - you increase the pulse width (constant fuel pressure), fuel pressure (constant pulse width), injector size (constant fuel pressure and pulse width). There is probably another case or two, but I can't think of them.

Let's assume the injector is operating in it's linear range.

You still have the same injectors but you need to inject bigger volume of fuel. So the question is HOW do you get it done?

As you said - you keep them open longer. Next question is - How do you do that?

You can do it a number of different ways - most obvious is adjust the fuel map, you could use a trim to apply to the whole fuel map, or some form of compensation table. I don't see how this has anything to do with the spreadsheet calculations...

You could put the smaller injector size in the ecu parameters (assuming it's using VE) so it thought it had smaller injectors and opened them for longer... but that seems like a pretty wrong way to do it given the other options.

Second part of your message speaks for itself. The bottom line here is that there are only two ways about it: you weither use the SAME injectors but hold them open longer by reducing the size in ECU, or you install proportionally bigger injector and open them about the same time as before- that is it from injectors size point of view.

...hold them open longer by reducing the size in ECU

I don't think that's the way anyone would recommend doing it... unless there were some limitations with the ecu...

Anyway, maybe someone from HPA can confirm if that is the intent of calculation in the spreadsheet.

Well, there are some ECUs that would allow you directly change injectors pulse width. Mine doesn't- it is stock Evo ECU. If i want to run my engine on e85 - how do i increase the volume of fuel injected?