I'm not up on JPI 930 installations but I did have an 830 installed in my 250 1-1/2 years ago. I had a number of other things done at the same time so I can't give you a precise installation figure but I believe 20 hours to install a 930 is unrealistically optimistic. Remember, your shop will need to remove a lot of 50 year old wiring and plumbing before they can even begin the new installation which itself is a lot of work. I would suggest 40 hours minimum, based on my experience with the 830.
Some other observations:
(1) I assume your installation will include an OAT feature. My remote JPI OAT probe was installed midway up the pilot's side of the fuselage, just behind the firewall. A simple and seemingly sensible location. Bad choice. The OAT probe picks up engine heat while in flight with the result that the temperature readout consistently displays an OAT that is 2 degrees C warmer than does my old original "meat thermometer" unit. If this inaccurate OAT information was being fed into a sophisticated avionics suite the magic calculations arising from it would be worthless. Installing the remote OAT probe in a different location will almost certainly involve additional labour, but whatever you do don't mount yours where mine is.
(2) Put some serious thought into where your 930's display is going to reside in your panel, as it may be difficult to read if your angle of sight is too oblique. Once again I can't speak with authority about the 930, but I can tell you that my 830's display is unreadable beyond 45 degrees. This difficulty of reading the display at oblique angles is virtually impossible whenever the display is bathed in direct sunlight. If your display is mounted on the far side of your panel and you need shield it from the sun with your right hand while simultaneously craning your body over the co-pilot's seat to read it you would be well advised to either fly alone or at the very least have an understanding passenger.
(3) I am acquainted with a number of owners who have various models of JPI equipment in their planes and every one of them reports trouble-free experiences. My unit was the exception, giving numerous spurious and erratic readings almost from new. My dealer spent a lot of time trouble-shooting and working with JPI's very good tech support people. JPI finally sent me a loaner unit so that they could have a look at my faulty unit. They replaced my unit with a completeley new unit without argument. The only problem is, their policy is to NOT compensate the dealer for warranty labour. Based on my dealer's shop rate, I would guess that my dealer has something like $800 invested in warranty labour in my unit which must be classified as "goodwill". I am grateful that (1) my avionics shop and my aircraft maintenance shop are sister companies, so there is no "passing the buck", and more important (2) that we have enjoyed a good, constructive working relationship that spans almost two decades. JPI evidently makes a very good product which they stand behind. I have no intention of slagging them over their warranty labour policy but sometimes things do go wrong and when they do there is no substitute for dealing with people who have become your friends.
Don Ostergard
c-flhv@magtech.ca