I couldn't find a post that indicates how to modify the SPEED value formula in evoscan to accomodate that I am using the sheptrans built 6 speed with a final drive of 4.09.

Besides feeling like my speedo is of, now my logs seem to be, which would be expected. I haven't corrected for the overall gearing change in the FD.

Can someone point me to a post or give me the equation info on how to make that adjustment. My formula is screenshot for reference. Maybe someone that has a FD (more common on the 5speed) can show me what theirs is and the logic used to get to it.

Can you just multiply the current formula by the % that your FD changed, same % that your speedo is off? If its reading 10% lower that it really is, multiply the current formula by 1.10.

Well, I am not really sure how this formula is used.

1.2427424*x

The different purely mathematically is 4.583 and 4.09, old to new FD value. So the variance is about 11%. So 1.11, but I am still missing how to adjust that value.

Do you believe I should 1.2427424*1.11 to get 1.379444064?

Or shouls it be less than, so that its 1.2427424*.89 to get 1.16040736?

Or is even modifying that number the correct approach?

whichever way makes it right. I think you would multiply it by 1.11. The value you get right now is low, right? All you should need to do is 1.2427424*x*1.11

just like a aftermarket speedo gear for a jeep with bigger tires...? except this is only for the logging, not the guage

this is purely speculation, but wouldnt hurt to try.