What is the most power a standard box can take before it breaks

Difficult question to answer.
The racing cars that are around today are up around the 150 bhp figure and still running. The mini gearbox was always an achilles heel and although it got betterover the years, it was never bullet proof.

I think the way it is used has more to do with its life than the amount of power it can take.
200 bhp ford twin cam motors have been bolted onto it with mixed successes.

As long as the gearbox is in good condition and you dont drive like an idiot it will last. Used to run my 1380 through a standard box with no problems.

It all depends how you treat it,

Boostedmini got 5 years out of a stock Mini-K box, with a 1360 turbo bolted to it running 15-20psi (~140-150HP).

I've run a MK2 S box for 12 years with a worked 1310 then a 1360 (120+HP) on it, and never broken anything in it.
But it has had layshaft, bearings etc replaced as needed whenever apart.

But if you make a habit of dragging a big power Mini off the mark and flat shifting into 2nd, I can guarantee the box will not be long for this world.

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Well drive any Mini like that and it wont like it, let alone a hi HP one!

_________________

I have a newly purchased Holden HQ one tonner with a 308 V8 and a M21 gearbox.

It dropped the gearbox a few weeks we bought it and the gearbox mechanic said the dropped gearbox was a direct result of "lighting up" the tyres and the like.

I am 58 years old and have never actually lit up tyres but the same applies to any vehicle - abuse it and it wont last long.

The beauty of smaller under powered recent cars is that its fairly hard to abuse them coz they just dont go. !!!!