isaacslaw,
Thanks for your answer, now I understand the area of the crack, yes I know that other guys have used glass cloth to strength the firewall but not for fixing a splited firewall where I was thinking it was the crack. I know that the YS 110 are very angry engines. About the pitts thanks for making it clear I didn't know I will have to remove part of the bottom of the firewall to allow the muffler to be connected, I'll stay with the stock. Some guys here use 2c engines and they have to do the same for the big mufflers. About the pictures thats OK you don't have to, you make it clear to me the area of the crack. If you still take them don't worry how it look, !QUOT!A pilot have to do what a pilot have to do to fly again!QUOT!.
