I didn't see any posts on here about this so here goes. I'm getting ready to do some heavy modifications to the engine on my 03 MCS and from what I've found of the transmission they come standard with, the Getrag GS6-85BG, they are only rated up to 255 ft-lbs. Now once I'm done with my engine I should be pushing close if not more than that and would like to know if anyone has done something similar and can direct me towards some upgrade gears or maybe a transmission swap. I've been doing some research and haven't found much.

 

If I'm not mistaken, everyone has used the factory transmissions, even with the few drag cars that were done.
Normally the weak point is the axles, but that also is normally only under heavy grip issues like using slicks.

Personally I wouldn't worry about the transmission unless you're well over 300 ft/lb of torque, esp in a street car with street tires.

 

+1. Some of the drag cars putting down 425-450wtq were even using the stock tranny. Heck, 1320 ran a 140mph quarter on the stock box.

If it does let go, i believe quaife makes a semi helical dog set for it...