I recently took a 360 mile round trip to pick up a new puppy, fuel economy for that trip was 40.06 mpg and on I-75 I was cruising at 74 mph.. Also had a week where I was really using a light throttle in all city driving and did 410 miles on 11.0 gallons of gas with at average speed of 26 mph. If you use the symposer to avoid engaging the turbo and adjust your speed so you can "time" the lights these cars are capable of suprising economy.
Notes on the FiST in regards to fuel economy.
Gas is important, run with 93 octane and you will observe a 3-4 mpg improvement compared to 87 octane when you aren't using the turbo. BTW, you'll also gain about 40 hp at the front tires on 93 octane. Bad news on this aspect is that there are a LOT of octane cheaters selling 87 octane as 93 octane. Sunoco on the New York Thruway has a history of octane cheating going back to the early 1990's. Was a time when I used to haul 5200 lbs. of boat and trailer with my 1985 Monte Carlo SS (weight transfer hitches work wonders). With the original 305 V8 engine knock was an issue, so I installed an Edelbrock Water Vapor Injection system and ever single time I had to fill with Sunoco I would have to stop the car, open the hood, and turn the water up to maximum. BTW, actually used a 3:2 mix of water and methanol because it provided superior knock control. Another more recent major brand doing octane cheating is BP, watched the fuel economy drop by 4 mpg on a trip to Charlotte, NC last Christmas after filling up at BP. My most honest and reliable supplier for good gas locally is hte Kroger fueling centers, not only get a discount for fuel points I also get 93 octane. On the road the most reliable have been Shell and Amoco.
Next, cooling is Critical. Ford designed these engines to run most efficiently at 195 degrees, stray 10 degrees lower or higher and you'll see a big drop in economy. This means that those 180 degree thermostats that are so popular are actually costing fuel and probably power. It also means that the factory radiator is undersized. I have the Mountune 3 pass in my car and on the way to the shop where the swap was done I was seeing 33mpg in the tattletail. On the way home from the shop I saw 37 mpg and I was driving into a 10 mph headwind. One minor negative for the larger radiator is that it does take longer for the engine to come up to temperature and when cold these cars do drink the gas with gusto. This makes for rather poor in city mileage in the winter, I usually see a 4 mpg loss in economy in the winter. Note, my sister lives in Lexington, VA and there is a grade on I64 that is 7% and about 4 miles long.heading into Virginia it's all downhill and the brake are needed to keep the speed down. Heading for West Virginia that grade is uphill and will put a Fiesta ST with the stock radiator into the limp mode when it's over 85. With my Mountune 3 pass I've taken that grade in 95 degree August and never saw more than 4 bars on the temperature indicator. To say I endorse this radiator would be an understatement, it is a fantastic radiator. I'll also note that in that August heat my car will roast the all season tires in 2nd gear.
The status on my car is such that it won't endanger the powertrain warranty. I have the Mountune intercooler, intake hoses, ST200 airbox, and hot pipe and boost hoses. Also have a Cobb Rmm and 2 1/2 inch cat back exhaust. From the warranty standpoint all I have done is increase the cooling capacity. So Hot Soak is not a concern and I have full power on tap at any ambient temperature. As for Tunes, it's the OEM Factory tune.
I keep pondering an upgrade in power but at present I'm traction limited. Yeah, I could get Race Spec tires and solve that but they are a bit pricey and these cars will always be traction limited to some extent. The other problem with upgrading the power is that the first step should be a good foundation and last time I check the MRX Long Block was pushing 9000 dollars. So, if I wanted to build myself a 400+ HP Fiesta ST the total cost for that will run 12,000 to 14,000 dollars. Frankly if I were to spend that kind of money on something I'm more inclined to use it for a Shotgun, say a Beretta DT11 or perhaps a Krieghoff.
