FWIW, comparing HD transmissions (T400 and 4L80E) vs light duty transmissions, and parasitic loss from Jake, of Jakes Performance. He specializes in T400s and 4L80Es which are pretty much identical internally as far as direct internal parts interchangeability. He states that the 2 HD transmissions only rob about .05 seconds over the lighter duty in a 10 second car, below that ET the loss is even less. This quote is taken from his frequently asked questions concerning parasitic loss. Of course either of the HD transmissions weigh more, because of the mass involved in making them strong in the original design.
Quote:
It is heavier, has more rotating mass, more clutch drag, and on the surface would seem to “eat” HP. The biggest loss would seem to come from the heavier rotating mass. However what is widely misunderstood is that yes it’s heavier, but that alone doesn’t cause more power loss. Remember an object in motion tends to stay in motion unless acted upon by another force. So unless there is more friction involved, a heavier rotating mass doesn’t take any more HP to maintain the same speed as a much lighter mass. It DOES take more power to accelerate or decelerate the heavier mass. So what this means to the average enthusiast is the faster your car, the more power the transmission will consume. This applies to all transmissions.
Power loss through the transmission will increase the faster you accelerate it. Our testing has shown that you will not see any significant power loss in a 11, 12 or 13 second combination. They simply aren’t accelerating fast enough that the rotating mass really comes into play. As you get into the low 10 second ¼ mile times, you may start to see some differences between a lightweight transmission and a heavier one. The thing to remember is, typically the lighter duty transmissions become a maintenance item at these power levels. More frequent rebuilds and failures. So for a small loss of power often equating to less than .05 second in Elapsed Time in the ¼ mile, you gain reliability. Unless you are racing for a record attempt where hundredths of a second are crucial, reliability is usually a more important factor.
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Jake was one of the top 200 4R builders in the country before switching his business model to the T 400 and 4L80Es, so I would believe he fully knows very well how much ET loss there would be in the lighter duty transmissions, compared to the heavier duty ones.