I recommend Downing/Atlanta wholeheartedly for their support. I called them four times: once before I bought it, to talk about concerns about engine longevity; once to talk about conflicts with a strut brace; once about how to set my timing with a J&S and the OBD II, and once to ask for the correct belt tension. There was no wait and I was helped promptly, courteously and competently each time. Wish computer support people were that way! It is a toll call, though.
If you cannot find the right gas, the Sebring can be temporarily disabled. Idle the car and look under the hood at the part of the Sebring at the drivers' (left) side of the car. Below a round plastic pillbox (for the current version of the Sebring only), you will find a mechanism called the bypass actuator. Slightly to the right of it is a metal bracket activated through a cable; this is your gas. Move the bracket to increase engine rpm a bit: you will see the actuator move. To disable the Sebring, use wire or similar to hold the bottom switch in the idle position. Now your car will behave as a standard Miata. Drive the gas tank really empty and refill with 93 octane before enabling the Sebring again.
I had some trouble with my belt. This belt is a speciality part, which you can only get from Downing Atlanta. The original belt had a problem, so Downing Atlanta FedExed me a replacement that I installed myself. I seem to have overtightened it, because it broke after only 6,000 miles. The way I understood the instructions, it has to be real tight. It says that the tension specification on the belt is 90 lb, but I have no clue how to measure that. It also says that there should be 3/8 inch deflection on the longest run of the belt under a 22 lbf thumb pressure, and I did the best I could with that.
I talked to Jim Goodrow at Downing, and he said there should be at most about a credit card thickness of space between the AC and power steering pulleys. I gave it a good credit card thickness of space and it does seem a lot less tight now. If it breaks again, I will note it here. I did put the belt on misaligned on one pulley and had to put it in the right grooves using a screw driver: I hope that I did not damage anything doing that; I did not see anything wrong.
After 35,000 miles, after putting in a new belt, one of the two plastic idler pulleys melted. Apparently, they have a habit of doing this. I replaced both pulleys with the new aluminum pulleys that are not supposed to fry.
Under normal driving, the Sebring is muted; it simply feels like you have a bigger engine. During cruise, it turns itself off so that there is no noticable penalty in mileage while cruising. But when you really step on it, the Sebring puts out an audible whine that is fun, and really pushes this light Miata forward.
If you should ever develop a problem in the supercharger, just disconnect the thing: you will not be stranded. If you cannot find the right gas (93 octane, or at least 92), you can disable the supercharger with a piece of wire. This failsafe operation was the main reason I bought the Sebring instead of more powerful options from Bell Engineering.
Downing/Atlanta does not say how much power the SC adds to the 1.8L engine; the statistics they give are for the 1.6L. I have heard 40 or 50 additional horsepower. As far as I am concerned, the most important thing is that it adds a lot of *torque* at low rpm, where a stock Miata really feels lethargic. The car is much nicer.
Well, I love it :)
Note that after I bought my Sebring, Downing Atlanta gave the marketing and support to Moss Motors (800) 235-6954.