Well, for those who thought you needed a naturally aspirated or electric assist engine to achieve unheard of mileage, think again!
Vehicle: 1998 Saab 900 S 2.0L Turbo 5 Speed Coupe.
MPG Modifications: Gutted interior, only 2 front seats (reduced overall weight by about 200lbs. Hi-flo filter + intake located right next to the engine (gets crazy hot.)
Trip: Belleville, NJ --> Pittsfield, NY = 180 miles each way over mountainous terrain.
Conditions: High humidity, partly cloudy in the low 80's.
Fuel: BP Ultimate (93+ octane rating on pump.)
Techniques employed:
- Acceleration on boost gauge remaining in -10 in/hg of vacuum. (gently depressing 50% throttle max.)
- Speeds not exceeding 65 mph using throttle. (GPS said 61, Speedometer said 63 typically.)
- Drafting behind large vehicles where roadway was full of cars... (never do this on the open road)
- Engine off neutral coasting down every incline. (Speeds vary, please be aware of local laws and speed limits.. lets just say "I got really far" after many of the hills with the engine still off. Vehicle brakes do not work with the engine off, keep this in mind if you are doing this at highway speeds. Simply let out the clutch to restart the car in 5'th gear once speed reduced to below 55 mph.)
- Neutral coasting during in town driving (it's much easier to maintain slow rolling speeds due to less wind resistance.)
- Always parked facing next direction of travel. (avoid unnecessary back-ups and turn around)
Luck factor: There was virtually no stops or traffic in front of me for at least 350 miles of my total trip. I chose good times to travel, and misses traffic on purpose.
It took 2.5 hours of constant downhill coasts I watched the MPG gauge go from the high 50's to the mid 70's for a while. Finally at the bottom of a hill it had maxed out at 99.9 mpg where it remained for the next 30 minutes before it's descent back down to earth at around 35 mpg (construction zones and traffic forced me to slow down out of my "sweet spot."
Stopped at the BP gas pump I had used to fill before leaving, mileage was reset to 0. Upon arrival it was 410 miles, the tank took 8 gallons of gas to fill back up. = 51.25 avg / mpg tank.
The plan for this vehicle was to be fun to drive and perform double duty as my race car, and gas mileage experiment. While some may argue burning up gas for fun at the racetrack negates all fuel savings, I tend to disagree. I find saving fuel to be a great challenge and equally as satisfying as running 13 seconds in the 1/4 mile or running a road course. The benefits of this vehicle aren't in the dollars saved, if money were my main concern.. I wouldn't drive an automobile. My Saab just goes to show "it can be done." You can have a fast / fun car that also sips fuel when off boost to the point that hybrid owners may be envious of.
I have recently purchased a laptop and run a program which basically controls all parameters of the ECU and how it operates the vehicle's engine. I'm working on several new maps, some for increased hp and performance, and some for ultimate fuel conservation. There's a fine line between sipping fuel and pre-detonation when it comes to turbocharged engines though. When reducing the amount of fuel going into the engine, one must also reduce the throttle input to match, or risk catastrophic engine failure.
This, my friends.. is my eco-modding story.
(The top row of pixels are out on my information display, but you can see for yourself.)