It was/is a popular thing to boost muscle car performance when dealing with automatic transmissions… the idea is to let the RPMs increase into the power band before actually engaging the transmission; all the while multiplying and releasing torque to the wheels. That way our “big block” muscle cars aren’t limping off the line unrealistically when exported to Beam 
(Sorry if this has been asked already, I did check the FAQ and searched for related topics prior to posting)
Jbeam editing is your friend I suspect.
I tried to dive into that yesterday and got so frustrated trying to learn Blender… The new 2.8 version is impossible to learn bc all the shortcuts are changed and thus are wrong in every tutorial I’m finding 
I’m okay with Fusion 360 but it doesn’t use quads for wireframes…
The jbeam lets you code in vehicle parameters, no modelling software required.
@NeTgHoSt In addition to the above link posted by Kyuu77, refer to these parameters in the JBEAM file and tweak as needed. Smaller converter diameters are the easiest way to raise the stall speed. When I design replicas, I usually refer to this website (https://www.floridatorqueconverters.com/) to get the exact diameter specs for the stock converter. Other than the stall torque ratio and converter diameter, I tend not to play with the other properties as I’m able to reasonably simulate what I’m looking for just changing those two things.
Good luck.
Wow, thanks for the awesome information guys! Didn’t know there was a way to tweak it in the code, will try this out soon on my 1967 El Camino with the TH350 3spd auto x)