How stong is my auto gearbox?

[luke01]

I have a 4spd auto box in my 1990 525i (what model box would this be?) I've recently fitted a turbo to my car (pics coming soon) and i'm in the process of setting it all up, adjusting things and such and i just wanted to know how much power the auto box will handle before it starts to fail? What would be the cheapest upgrade option, stronger auto box, or a manual (i'd prefer manual). Thanks.

[BillionPa]

i would tune for max torque at about 290NM, or go for a manual.... manual would probably be cheeper, since a stronger auto box would be from a 540, and you would need all kinds of parts to do that retrofit.

[Jay 535i]

I'm no expert, but I've seen this question asked before. The answer always seems to come back: manual. It's inherently much stronger, plus much more fun -- especially if you're turbo'd.

[ILoveMPower]

Not strong enough, look for a 5-spd swap.

The stock manual system has been known to take 500hp, with only a clutch.

[Gene in NC]

Check the

mye28.com

site. They have 3.5 turbos. Have heard of ATs behind. Ur AT essentially same as theirs.

[luke01]

manual seems the way to go them, i'll investigate it further in the very near future.

[BigKriss]

The e23 745i had a zh-4hp22 gearbox with 400nm as standard.

[pundit]

i would tune for max torque at about 290NM, or go for a manual.... manual would probably be cheeper, since a stronger auto box would be from a 540, and you would need all kinds of parts to do that retrofit.

A 1990 525 should have a ZF4HP22 which is the same autobox the 535 (M30) uses.
The M30 has 300nm of torque as standard.
So a 4HP22 should be able to handle more than 290nm.
However fitting a turbo and then limiting the power to no more than 300nm is like taking viagra and practising abstinence.... it's basically a screwed up concept.
I'd fit a five speed manual box and forget about limiting the torque.

[genphreak]

manual seems the way to go them, i'll investigate it further in the very near future.

I'd expect it to be strong enough to get you by for a while at least. If you aren't sure how worn she is, perhaps try to avoid maximum power when going through the gears... especially 1st to 2nd (these surfaces wear the most in use).

Change the filter and o-ring (be sure to remove the old one) and maybe run Castrol Synthetic ATF, (Transmax Z) as it is the only ZF approved synthetic for your box. Heat may get higher than the it was designed for, so I'd want the best possible ATF to take good care of her. Your box (if it is a ZF4HP22) is the same as the one on a 535, so its definately stronger than you need anyway.

I might be corrected but I reckon running a turbo you could kill a manual tranny more easily than the ZF. You do have the ZF not the GM box right? I've NFI about the GM trannies.

Nick

[genphreak]

The e23 745i had a zh-4hp22 gearbox with 400nm as standard.

Yea, good point. Heavier car that too.