3 of the 4 mainfold studs in my greddy are broken , i now it happens sometimes how do you guys took the broken stud from the mainfold and what studs did you use to replace them .

 

Type "Greddy Studs" in the search function. It will come up with tons of results. Better for you to just go read them.
Short answer, drill a pilot hole sized for an easyout or reverse drillbit. Soak the threaded holes with a penetrating oil and then pray your easy out doesn't break off in the studs. You might be better off having a machine shop do it for you if they are rusted in there real bad.

 

....or you can take it to a machine shop and have them take them out for you and also have them re drill it to accept bigger studs.

 

Do you mean studs or bolts? If you try to extract the bolts with an easy-out and it breaks you will be screwed...It is a gamble....the easy-out is significantly harder and will be a pain to drill out (dull your best bits)....If you like projects give it a try...if you want it to be done quickly and done right...take it to a machine shop and have them drill out the 8M bolts and have them tap for 10M bolts as well as increase the turbo side bolt holes and you should'nt have this problem in the future....Remember never reuse turbo bolts (too much strain on the bolts twisting with that many high heat-cycles)...Also always use High-Heat Anti-seize....on the threads