How much horsepower can this trans handle with a trans-go shift kit until I need to start getting it beefed up or until it could break?

 

my tranny died on my first dyno pass. did 434.6rwhp first pull, then wouldnt even hit 150rwhp after that. rebuilt, but not to my likings but no extra cost. need to redyno. if you need a rebuild, check out cpt. frank make a bulletproof tranny for a decent price. its where mine will be going soon.

 

I would say the limit on a stock trans is around 400 RWHP mine is about there and hasnt broken yet, then again im not very hard on it.

 

I agree that 4L60E's are usually good up to 400 rwhp. After that you better plan on a beefed up 4L60E like Speed Incs stage 3 for example. After 500rwhp I would ditch the whole idea of a 4L60E because even the built ones won't last. Then your better off looking at a 4L80E or TH400 conversion.