Ok as of now I have a fully forged 383 stroker with the lt4 heads intake cam ect it's the full lt4 kit I'm kit happy with the cam and would like a more aggressive one how much hp would I gain switching over to a fm 847 with that setup thanks

 

Since you didnt state that the heads you have are stock or ported. I'll assume they are stock. You will gain a little but dont expect alot. You wont be any faster than a bolt on/ cam only setup. Maybee 360-365rw.