my bonnet is cracking really bad, its fibreglass and im gonna change it, if I get a bonnet buldge will it stiffen up?? or is there another way,

A bonnet bulge would help to stiffen it up a tad as it adds more shape, id the bulge for the cracking bonnet or the new one?

buldge is for new one.

A seperate bonnet bulge IME is not worth the hassle and a new bonnet with one built in is far superior. Depends really on whether you're spraying up or not as it could hide the join if you do.

do mk do a bonnet with built in buldge? if not where can I get one??

Yes, they do. It's listed on their site at about £130

Cheers

Rick