At what point do motor mods force tranny mods?

I'm curious too. Wondering how much HP before the tranny needs to be replaced, especially the 3650.

You are pushing it too far when stuff breaks. Most of the people running 400 hp are also doing it on street tires. Street tires are never going to grab hard enough to break most drivetrain components. At the same time, a 260-280 rwhp car with a well-designed suspension and some sticky tires can obliterate the 8.8 rear end in its stock form.

A lot more than power numbers comes into the equation.

My point was not to give an exact answer, as there is no exact answer. The answer can't be anymore specific than 'When you break something, you have pushed too far.'

If someone can get Nittos to hook hard enough to break something, then yes, even a set of Nittos is too much. But suppose I can buy a set of Nittos, and get them to hook hard enough to scatter the diff. Suppose you buy a set of E/T Drags, and are unable to properly use them (and as a result you simply smoke them every launch). It would be incorrect to say that my drivetrain was weaker than yours, as the driver plays just as big a role as does the tire compound, as does the suspension.

My point is simply that there are too many variables in your equation to allow you to point at any one or two and draw a line which cannot be crossed.

I agree, when it breaks you know it can't handle it.

Ditto, drive that sumbiotch till she breaks somethin. No use in upgrading it till you have the ponies to shatter it...