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# Limits of injection timing, adding more fuel

### Diesel Tuning Fundamentals

Discussion and questions related to the course Diesel Tuning Fundamentals

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So what are the limits of injection timing? what happens when we add 100 percent bigger injectors, what are the formulas to use for bigger injectors, fuel injection pump, how much timing do we add for every gram of fuel?

There's a lot of factors that you've just mentioned there Daniel and as explained in the course, they all have an effect on each other. For example fitting a set of injectors that are double the size will let you inject the same mass of fuel in half the time (all things being equal). As a very rough guide, I try and keep the EOI point close to TDC so if you're logging the injection SOI and EOI this will guide you in your timing target tables. I'd always suggest basing your timing on the stock timing tables and I wouldn't stray too far from the factory numbers - This is why larger injectors and higher fuel pressure are our friend when it comes to making large increases in power. We can keep stock or close to stock timing but still deliver a much large mass of fuel.

As for your question about timing per gram of fuel, it's not that simple. You need to consider what the required pulse width is to deliver that fuel and then consider for a given rpm what that pulse width looks like in terms of crankshaft rotation. From here you can decide what the SOI point would need to be for example to have EOI occur at TDC if that was your aim.

Andre, do you know if there is a way to have HP Tuners display the EOI point for a Chevy Duramax diesel? That would be super helpful. Otherwise, I guess there are some spreadsheets that may assist, but the interplay between fuel pressure, fuel amount, and injector size is so complex, it's difficult for me to imagine that a spreadsheet would be able to be very accurate.

In other words, I don't think I could hope to give the spreadsheet accurate enough inputs, and therefore, garbage in -> garbage out..