When ET and MPH Are Not a Match?

Some calculators post results based on "ideals", ideally tuned engine, ideally tuned suspension

ET is a function of how well the chassis performs, and that shows up in your 60 foot time, the lower the time, the better your chassis works, shocks, springs, converter comes into play here also if automatic, clutch if you run a standard, it's how hard you hit the tires to plant them, to get the car moving. As a leaf spring car, you want the body to rise in a slow controlled fashion; you do not want the car to look like it's hopping down the track like a rabbit, that is when the suspension is coming to the end of shock travel and unloading the suspension. You want to think Sir Isaac here; for every action there is an opposite and equal reaction; as the body rises, it is pushing down on the tires, control it.

MPH is purely a function of horse power; it takes so much power, to move so much mass, at some velocity. I won't say it's simple Physics, but it is Physics just the same.

Your 12.72 ET on a 108 MPH is not way out of line, what was/is the elevation, what was the temperature?? These are factors not accounted for.