My father was born out of wedlock in 1931. My grandmother married in 1935 and her husband adopted my father although I'm not sure what year. Would his original birth info have his biological father's name and if so would I have access to that

On our page regarding Birth Records it states who can obtain access to birth records for births that have occurred within the past 92 years (yes you can if you prove you're next of kin). There is also a link to the Registrar General where you can find the necessary forms. With an adoption however his original birth registration may have been pulled and replaced by a new one. And the information on either would be whatever your grandmother provided.