Thread: SD Fuel Factor and the effect on fuel map resolution

NismoTronicSA SD factor and fuel map resolution

It has been asked by a few people in the past weeks about how to properly setup the SD factor in your tune for the greatest resolution. The trick here is to maintain enough range to cover the load points you need to cover and to have enough resolution in the map that changing the fuel table by 1 unit does not cause a big swing in fueling.

When I refer to range I am simply referring to your load scale. You want to be able to give the tune enough fuel to cover the load scale you will be using.

[INDENT]

• Fuel table (0-255) which is a 8-bit system. The fuel table can only be setup to use the values 0-255 .. but depending on what your SD factor is set to, these values can vary greatly as to how much fuel is actually being delivered.
• SD Factor - The SD factor is basically how much "weight" is applied per single unit in the fuel table. The base Injector Pulsewidth calculation for a Speed Density TCD is calculated by multiplying the Fuel Map Value x SD FACTOR.
  

For example lets say your SD factor is 150 and on your fuel table you have values of 1 and 200.

1. If your SD factor is 150 and your fuel table value is 1, then your base injector pulsewidth is 150 x 1 = 150
2. If your SD factor is 150 and your fuel table value is 200, then your base injector pulsewidth is 150 * 200 = 30,000
   

Now lets say your SD factor is 255 and on your fuel table you still have those same values of 1 and 200.

1. 1) If your SD facot ris 255 and your fuel table value is 1, then your base injector pulsewidth is 255 X 1 = 255
2. 2) If your SD facotr is 255 and your fuel table value is 200, then your base injector pulsewidth is 255 * 200 = 51,000.[/INDENT]
   

As you can see there is a pretty large difference between a value of 200 at a SD factor of 150 and that same value of 40 at a SD factor of 255.

So with a SD factor of 255 you can see that you have more RANGE in the fuel table but you can also see that when you change a fuel table value by just a single unit in either direction that there is a much bigger difference in fueling, thus LOSING RESOLUTION.

So, the question that arises is "How do I get more fuel if I don't want to raise the SD factor so high that I lose low end resolution?!"

Well, that answer actually comes in two parts.

The first part is simply changing your current OR old injector size to scale your fuel map UP so you can get into the range that you need to be. DO NOT GET CAUGHT UP ON WHAT THE INJECTOR SIZING SAYS .. again it is simply a scalar and sometimes you will find that the car will run better at a smaller current injector size than what your injectors are listed as. This isn't a "work around", it is simply moving your fuel scaling around and it can be extremely helpful in getting things much closer without touching the SD factor and thus losing resolution!

The second part is a table that some people completely neglect and/or don't know even exists and that is the Boost Fuel Trim Table. This table allows you to add more fuel as your boost pressure increases without actually adding the fuel to your fuel map, since trying to add more to your fuel map will require you to extend the RANGE of the fuel table and thus losing resolution!



The way I like to tune this table is to tune the car to wastegate pressure if under ~14psi and then make your fuel table practically the same values from your wastegate pressure all the way up to your higher boost pressure. Doing it this way allows you to have enough range in your fuel system WITHOUT changing your SD Factor and it also allows you to maintain your low load resolution so when you are making a small adjustment to your fuel table it doesn't change the injector output soooo much that it causes big swings in your AFR.

Ok, I see what Dave was saying now. Makes sense. Good info.

In the video I found on your youtube, you had the option to 'optimize sd fuel map' if you right click on the fuel map. Is that feature not seen in the demo version downloaded from the nismotronic site?

Correct, that feature is not enabled with the demo version of the application but is fully functional in the release version.

I never noticed that. What exactly does that do?

Well that's pretty neat!

With everything this ecu can do, what plans and features are in the works?

Likely there will be a few more software improvements, including better logging.

But as far as firmware is concerned; we will entertain requests for additional features.

Honestly, a turbo timer would be cool. Not sure how that would be pulled off, maybe using one of the outputs? Idk