What's the limits of the 4r70w?

[marauder4.6DOHC]

Doing a Eaton swap and I am just wondering at what hp I should start worrying about the trans going out?

[Zack]

525 with a J-mod

[Pat]

If your tranny has not been rebuilt it's not the added horsepower thats of concern but the parts that normally wear out over the years. So, a rebuild, clutches, OD band, seals and any worn metal parts, should be replaced. There are members on this site who specialize in the 4R70/75 that could advise you on what to expect, costs, etc.