My Megasquirt adventures over the years
And now the main event, the VE table:
*cue angelic choir sounds*
In short, this table is more or less the mathematical model of airflow through your engine. VE stands for "volumetric efficiency" and relates to how much air gets pulled into the cylinder relative to the actual volume of a cylinder. So if you have a cylinder that's 1L in size and you have 100% VE, that cylinder has 1L of air in it at the pressure on the Y axis of the graph before compression starts. It's probably more nuanced than this, but that's a pretty general simple way to think about it. This is where you'll likely spend most of your tuning life. This table should generally also resemble the torque curve of your engine. The same table exists in HP Tuners:
Dodge also likes being silly by inverting the Y axis compared to MS, but that's neither here nor there. I searched high and low trying to find these values before I downloaded HP Tuners and got lucky that my engine was in their sample files. However, this one was also unfortunately not as straightforward to copy directly to MS. In my case, I think it was largely because of my engine changes though (headers, cam, intake). If I had a stock engine, I bet these would have copied over fairly well to give me a good place to start. I still used them as the basis for my tune and have let autotune do some work to tweak things as these should at least get me in the ballpark. You can see where the values peak around 4300-4500 rpm here, which corresponds to the torque peak of the engine on the dyno chart:
You can also see that other tiny little hump around 2500 on the curve reflected in the VE table.
However, with great power comes great opportunity to mess things up as well. The VE table can disguise a lot of things and can be used in a lot of different ways that may or may not be a good idea. For instance, you could in theory bake some amount of "accelerator pump" into it if you wanted by artificially increasing the values at low rpm and high load. Or, if you have the incorrect size injectors, you can scale the VE table to make up for it. I've certainly been guilty of the latter of those two, though it was partially because I didn't know my actual injector specs. It all comes down to the fueling equation that the MS uses. In simple form, it's the following:
PW = required fuel * VE * load * MAT correction * CLT correction * EGO correction + acceleration enrichment + dead time
That's a lot of different knobs you can tweak that will all kind of do the same thing in some regards. The goal in my book is to avoid the "easy" road of using one to cover for the other as it usually will cause some other knock-on effect down the road. The VE table is the core of your engine model, so ideally you want it to be as accurate and unrelated to anything but airflow as you can get.
The last setting on the fuel tab (that I have at least) has to do with controlling your fuel pump. My setup is pretty simple as I just have an on/off pump that is manifold referenced for pressure, so the fuel pressure relative to the intake is always the same (in theory). This makes the fueling calculation a little easier. There are lot of other fun things you can play with in here like individual cylinder trims (like if you have a lean or rich cylinder because of bad air distribution or something) and some other fueling corrections for things like fuel temp (which the OEM computer does). I don't have a fuel temp sensor (yet at least), though I do have a pressure sensor, so I might play with these down the road, especially as I seem to have problems at hot idle with my mixture leaning out that other correction factors haven't addressed yet.
There are also other settings in there for EGO control like authority tables where you can adjust how much it can change the mixture by based on where on the map you are instead of a fixed value. So for instance, you could let it adjust by 10% at idle, but only 5% at cruise or something like that. I haven't gotten that far into it yet as generally speaking I want EGO to be the last thing I tune, not the first.
So that's probably enough ranting for my second session. Next up will be the meat of the meat and potatoes, ignition settings.
And now the main event, the VE table:
*cue angelic choir sounds*
In short, this table is more or less the mathematical model of airflow through your engine. VE stands for "volumetric efficiency" and relates to how much air gets pulled into the cylinder relative to the actual volume of a cylinder. So if you have a cylinder that's 1L in size and you have 100% VE, that cylinder has 1L of air in it at the pressure on the Y axis of the graph before compression starts. It's probably more nuanced than this, but that's a pretty general simple way to think about it. This is where you'll likely spend most of your tuning life. This table should generally also resemble the torque curve of your engine. The same table exists in HP Tuners:
Dodge also likes being silly by inverting the Y axis compared to MS, but that's neither here nor there. I searched high and low trying to find these values before I downloaded HP Tuners and got lucky that my engine was in their sample files. However, this one was also unfortunately not as straightforward to copy directly to MS. In my case, I think it was largely because of my engine changes though (headers, cam, intake). If I had a stock engine, I bet these would have copied over fairly well to give me a good place to start. I still used them as the basis for my tune and have let autotune do some work to tweak things as these should at least get me in the ballpark. You can see where the values peak around 4300-4500 rpm here, which corresponds to the torque peak of the engine on the dyno chart:
You can also see that other tiny little hump around 2500 on the curve reflected in the VE table.
However, with great power comes great opportunity to mess things up as well. The VE table can disguise a lot of things and can be used in a lot of different ways that may or may not be a good idea. For instance, you could in theory bake some amount of "accelerator pump" into it if you wanted by artificially increasing the values at low rpm and high load. Or, if you have the incorrect size injectors, you can scale the VE table to make up for it. I've certainly been guilty of the latter of those two, though it was partially because I didn't know my actual injector specs. It all comes down to the fueling equation that the MS uses. In simple form, it's the following:
PW = required fuel * VE * load * MAT correction * CLT correction * EGO correction + acceleration enrichment + dead time
That's a lot of different knobs you can tweak that will all kind of do the same thing in some regards. The goal in my book is to avoid the "easy" road of using one to cover for the other as it usually will cause some other knock-on effect down the road. The VE table is the core of your engine model, so ideally you want it to be as accurate and unrelated to anything but airflow as you can get.
The last setting on the fuel tab (that I have at least) has to do with controlling your fuel pump. My setup is pretty simple as I just have an on/off pump that is manifold referenced for pressure, so the fuel pressure relative to the intake is always the same (in theory). This makes the fueling calculation a little easier. There are lot of other fun things you can play with in here like individual cylinder trims (like if you have a lean or rich cylinder because of bad air distribution or something) and some other fueling corrections for things like fuel temp (which the OEM computer does). I don't have a fuel temp sensor (yet at least), though I do have a pressure sensor, so I might play with these down the road, especially as I seem to have problems at hot idle with my mixture leaning out that other correction factors haven't addressed yet.
There are also other settings in there for EGO control like authority tables where you can adjust how much it can change the mixture by based on where on the map you are instead of a fixed value. So for instance, you could let it adjust by 10% at idle, but only 5% at cruise or something like that. I haven't gotten that far into it yet as generally speaking I want EGO to be the last thing I tune, not the first.
So that's probably enough ranting for my second session. Next up will be the meat of the meat and potatoes, ignition settings.