Originally posted by jesus420a
The A604 tranny won't hold as much. If you do boost it, it will hold about 8psi tops. if you go over the clutches will start to slip.

first, use the search function. this has been discussed numerous times throughout the years.

next, that's a strong statement and false. although not recommended daily, they'll hold upwards of around 15psi (giving into accnt the condition of the clutch packs and overall trans). If you don't have a trans cooler, GET ONE. DO NOT boost w/out it. I boosted for years from 6 to 10psi on a worn ATX and never slipped once.there's some people that I've read in the past that have gone as high as 18psi with no slips.

My recomendation?
if you're not built, you'll break the motor before the trans, so boost away.
if you ARE built, don't go over 12psi. also, stay away from long pulls. This will bring up the temps of the ATX fluid to very high levels. Heat is what kills A604's mostly, not power.