Racing Coupes

hello...
Can someone help me how to strengthen the transmission that he can stand of 550 horsepower ... I already broke the gearbox twice

Which parts in the gearbox have you broken?

I have also broken two gearboxes, but I have now fitted a Quaife differential, which appears to have sorted the problem

The first gear when the jumping places we crack
Third gear we crack twice
As time passes is formed between the doubled waves freedom of gears
I saw that strengthen the shell of the gearbox

Which kind of racing you are about? On drag racing first to go is diff in my past FWD experience. Mentioned quaife is suggested step(or factory Q2, but its probably slightly weaker unit).

I broke 3rd gear on strenghtened integrale gearbox(housing and bearings, and cryothreaded as bonus) on fast "street" driving.

There exist a group N kit from italy (multiple manufacturers), which consist input shaft and first 3 gears. Its simple swap for OEM parts, but its designed for integrale and with little more work also on 16vt or early 20vt 5 speed.
I used them to rebuild my box, but not much drive it yet due engine went down(never ending story).
Cost around 1500-2000eur dealer depend and no claimed torque capacity figures.
Maybe better to go for dogbox if pure race car, but its almost triple price.

Last to mention, some harsh clutch will not help either. I used tripple palte sintered APracing and gear broken on low boost just after shift.