I just put together a fast and dirty sound pack for the S-55. I took a copy of the stock Robinson sound pack, then replaced the motor sounds with those from Doug Smith's Harvard sound pack (Pratt & Whittney R-1340 all the way baby!). It probably isn't totally accurate, but it sure beats the dickens out of using the Robinson sound pack.
I do want to do a bit of work to the rotor sounds as they are very light for a chopper the size of the S-55....and get Doug's permission to use his files in the sound pack.
Give me a couple days and I should have it uploaded...or that's the plan anyhow. OBIO