My Megasquirt adventures over the years
Next up is some more nuanced stuff with injectors, though this one is maybe less important depending on your setup. From what we could see in the last post, when the injector first opens, it doesn't want to flow linearly (at least these injectors don't, maybe there are some out there that are closer). You'll notice though, that by ~2ms or so, the line is pretty straight and follows the linear curve. What this table does is scale the pulsewidths to adjust for that nonlinear region:
So, do you need to do anything with this? It will depend on your injector sizes. I put in the values because I spent a lot of time in Excel making those graphs and trying to understand how Dodge characterized things vs how the Megasquirt does it, but the reality is that my injectors almost never run under 2ms in practice. At idle or cruising down the highway, I tend to be in the 3-5ms range, so this was all just "for funsies" for me. However, if you have really big injectors, like for a boosted application maybe, you could very well find yourself in this region of flow. What this curve does is basically just overwrites a calculated pulsewidth from an expected linear flow into the pulsewidth required to get the actual amount of fuel desired. Going back to our previous graph, you can think of it as drawing a line horizontally from the linear flow line over to the actual flow line and checking the difference between the injector times.
So for example, say the Megasquirt calculates that we need .001 grams of fuel for a particular cycle. Based on the linear flow rate of the injectors, that would correlate to a pulse width of ~1ms. However, in reality, the injector hasn't even started flowing fuel yet at that pulse width. So you keep following the line over to where it intersects the actual fuel delivered line and then go down there to see the actual pulse width required to deliver 0.001g of fuel:
So the thing to remember is the red line is expected/calculated fuel, and the blue line is actual measured fuel delivered. In the MS table/curve, you would say for an original pulse width of 1ms (the "original" fuel value), instead use the "new" fuel value of ~1.35ms. It took me a while to figure out how to interpret the "original" vs "new" pulse width idea, but I'm fairly certain this is it. Does it really matter for me? Probably not, but it makes me feel good that I think I have the correct values in there regardless.
Similar story here to the previous one where you can set different values for different injectors. So if you went back to the setup where you might have injectors for pump gas and different ones for a race fuel, you can set them individally here. Neat stuff, though probably something very few people will ever need to touch unless you are running a more extreme engine setup.
Next up is some more nuanced stuff with injectors, though this one is maybe less important depending on your setup. From what we could see in the last post, when the injector first opens, it doesn't want to flow linearly (at least these injectors don't, maybe there are some out there that are closer). You'll notice though, that by ~2ms or so, the line is pretty straight and follows the linear curve. What this table does is scale the pulsewidths to adjust for that nonlinear region:
So, do you need to do anything with this? It will depend on your injector sizes. I put in the values because I spent a lot of time in Excel making those graphs and trying to understand how Dodge characterized things vs how the Megasquirt does it, but the reality is that my injectors almost never run under 2ms in practice. At idle or cruising down the highway, I tend to be in the 3-5ms range, so this was all just "for funsies" for me. However, if you have really big injectors, like for a boosted application maybe, you could very well find yourself in this region of flow. What this curve does is basically just overwrites a calculated pulsewidth from an expected linear flow into the pulsewidth required to get the actual amount of fuel desired. Going back to our previous graph, you can think of it as drawing a line horizontally from the linear flow line over to the actual flow line and checking the difference between the injector times.
So for example, say the Megasquirt calculates that we need .001 grams of fuel for a particular cycle. Based on the linear flow rate of the injectors, that would correlate to a pulse width of ~1ms. However, in reality, the injector hasn't even started flowing fuel yet at that pulse width. So you keep following the line over to where it intersects the actual fuel delivered line and then go down there to see the actual pulse width required to deliver 0.001g of fuel:
So the thing to remember is the red line is expected/calculated fuel, and the blue line is actual measured fuel delivered. In the MS table/curve, you would say for an original pulse width of 1ms (the "original" fuel value), instead use the "new" fuel value of ~1.35ms. It took me a while to figure out how to interpret the "original" vs "new" pulse width idea, but I'm fairly certain this is it. Does it really matter for me? Probably not, but it makes me feel good that I think I have the correct values in there regardless.
Similar story here to the previous one where you can set different values for different injectors. So if you went back to the setup where you might have injectors for pump gas and different ones for a race fuel, you can set them individally here. Neat stuff, though probably something very few people will ever need to touch unless you are running a more extreme engine setup.