You're only thinking of full-throttle when you actually make more power using the extra air and fuel. When driving "normally" and cruising steadily, you're not using more air+fuel with a turbo. You actually use less because now you have expanding hot exhaust energy spinning the turbo and helping push air into the intake (even if you're not making boost, the turbo is still helping some). Without the turbo, that exhaust energy is just dumped out the tail pipe and the engine has to work harder to suck air past the partially open throttle body, requiring more air+fuel to output the same net power to the wheels to maintain the same cruising speed.
My completely unscientific observations based only on memory seem to indicate that I'm generally getting about 2 mpg better with the turbo for my usual daily driving to work. My dashboard average economy readout pre-turbo would always eventually settle into the 18-19 mpg range for me. With the turbo, now it seems to settle into the 20-21 mpg range after several days of just driving "normal" (with at least one full throttle blast through 1st and 2nd gear each day). This seems in agreement with Snarf's observations.
My 28 mpg trip was from abnormally gentle driving and not exceeding 70 mph on the freeway. It's nice to know that it's possible, but I'll probably not see such a high number again for a long time
I seem to be able to hit 25 mpg pretty easily when doing a lot of freeway and highway driving, as long as I stay around 70 mph or less. Bumping the speed up to 75 mph seems to drop fuel economy down to about 21 mpg.
The turbo will pay for itself much faster in fuel savings than big tires or a lift It's nice to have a fun mod that doesn't DECREASE fuel economy.
Remember to take into consideration the price difference between regular and premium fuel (turbo requires 91 octane). Here's the formula to calculate how many miles it will take to save a target $ amount:
[miles to save $] = [target $ to save] / ( ([regular fuel price] / [pre-turbo mpg]) - ([premium fuel price] / [post-turbo mpg]) )
If the result comes out negative, then it means you'll LOSE your target $ amount in that many miles!
And here's the formula to calculate how much $ you'll save after travelling a specific number of miles:
[$ saved] = [miles traveled] x ( ([regular fuel price] / [pre-turbo mpg]) - ([premium fuel price] / [post-turbo mpg]) )
If the result is negative, then of course that means you lost money.
Formula explanation: Dividing fuel price (in $/gal) by fuel economy (in mpg) gives you the cost to drive the vehicle in dollars per mile (henceforth, "DPM"). Multiply your DPM value by a number of miles to determine how much it costs to travel that many miles ($ = miles x DPM). Divide a dollar amount by your DPM value to figure out how many miles you can travel for that amount of money (miles = $ / DPM). The formulas above simply involve calculating a pre-mod DPM and post-mod DPM, then subtracting pre-mod-DPM from post-mod-DPM to get a "change in DPM caused by the mod" (henceforth, "delta-DPM"). Your delta-DPM then is used to calculate a change in cost to travel a specific number of miles (delta-$ = miles / delta-DPM), or a change in how many miles can be traveled by a specific dollar amount (delta-miles = $ / delta-DPM). The full formulas above are slightly rearranged and simplified to avoid some extra negatives and make more sense for the specific situations we're talking about. In pure form, savings would be be represented as a negative change.
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