How to make my box stronger

[RallyRS]

Hi,

I have a 1989 Legacy RS turbo 4WD rally car. Have done some work to engine, turbo, injectors, ecu, exhaust, inlet. I'm having problems with it blowing gearboxes. Normally ripping teeth off 2nd or 3rd, but also breaking keyway on 5th.

Has anyone got any tips to make these box abit stronger?

I haven't got enough money to buy expensive boxes. Unsure of price on hardened gears.

I heard that you can buy hardened steel keyways, but unsure if it would help??? Any know?

Any tips would be great.

Cheers
Hayden (RallyRS)