The four, members of the Finks outlaw motorcycle gang, were arrested during dawn raids in neighbouring suburbs on Tuesday more than four months after police were called to a blood-splattered room at the Vineyard Hotel in the city's northwest.

Cleaners called police on December 18 after they made the grisly discovery. The subsequent investigation led detectives to arrest the men, aged 22, 24, 27 and 35.

Police will allege in court the men kidnapped and detained another man, demanding cash, and physically and sexually assaulted him over a number of hours in the hotel room.

The four were refused bail to appear at Blacktown Local Court on Wednesday.

A 30-year-old woman, described by police as an associate of the gang, was also arrested on Tuesday and charged.

She was granted conditional bail and is due to appear at Blacktown Local Court on May 29.

Detective Superintendent Deb Wallace says the victim's injuries included a loss of hearing in one ear from being repeatedly beaten at times with a "wooden instrument".

He was allegedly stabbed in the knee and had boiling water poured over his upper body to remove his club tattoo.

Police believe he was with the alleged attackers for more than 12 hours.

Det Supt Wallace said police had to work hard to gain the victim's confidence so they could prosecute the "most serious offences".

Australian Associated Press