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I have the turbo on mine with not so many miles on it but I can tell you with 100% accuracy that I have had my foot to the floor since the day I got the turbo done and my millage just keeps going up. Granted I am not at 50+ MPG but I reset the counter and it started at low 20's and is up to 30+ and keeps going up every time I drive it. I will have more info on it as time goes on.
 

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Not trying to be an @$$ here, but the only way to make any sense of real gas mileage is to use the old fashion way of full tank to refill and mileage driven. Mine can show 20 miles per gallon difference in the display to real measures at times.
 

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Not trying to be an @$$ here, but the only way to make any sense of real gas mileage is to use the old fashion way of full tank to refill and mileage driven. Mine can show 20 miles per gallon difference in the display to real measures at times.

I agree however, most newer computers take a LOT of sensor inputs and most are accurate within 1 or 2 MPG. You would also need to fill up and drive and then refill up and drive multiple times while doing the math over time to get an accurate estimate and even that can be drastically skewed based on when you fill up and the temperature outside and how long you idle your car and things like that. the computer actually takes idle time and temperature and things into account in most newer computers. Don't get me wrong I think to get an accurate measurement you would need very controlled situations such as a temperature controlled location with a dyno and a few days of testing. I personally think the computer is accurate enough to get us very close to the mark after extended driving.

One example of how temperature can skew your results is fuel density. When it is really cold outside and you fill your car the fuel molecules are more dense and because of this your actually getting more for your money if you fill up in the early morning than if you fill up at noon. Granted this is not really something you normally see huge changes in during any given day however, if you have noticed you actually will get more dense fuel in the winter than the summer because of this effect. Because the gas tanks are stored underground the difference during any single day is pretty much not noticed.

Another factor is even the gas pump itself they are calibrated to be most accurate at their highest flow rate. If you use the lowest fuel flow rate then you actually get more gas then what the gas pump is reading.

Based on all of this even filling up, driving, filling up again, and then doing math is still not super accurate and probably worse than the computer because of human error.

Im not trying to say anything bad about anyone I am just saying my honest opinion is that the computer is probably accurate enough to get us in the ball park of 1 or 2 MPG of the real number.
 

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Most on board MPG meters simply calculate injector pulses/distance traveled using the factory equipment and ECU settings as its base of information. If your equipment (injectors) and/or programming have changed to alter the amount of fuel delivered chances are your MPG meter is no longer correct.

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@Funinthesun and @Orangeman are correct, one has to set TripA to zero, fill up, and at next fill-up divide TripA by gallons. It'll be close enough to get a rough idea. After 3x one should have a somewhat stable number for their driving, weather, and setup. Everyone will have something different, but it's a good baseline. The computer cannot be trusted because it has no idea what the turbo setup is, as FunInTheSun and OrangeMan said.
 

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I highly doubt people are getting this kind of MPG, I echo the others. It is because the ECU was reprogrammed and is inaccurate. I can't wait to see what mileage you are getting from a full tank. I have not did this myself, I should! I will tell you this, I make a trip to Deltona to see @gpcustoms and it seems about the same amount of gas used before and after turbo install. I have not had an ECU reprogram though and @kenny_h has and he feels he has seen a increase in MPG.
 

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Went to the gun range last week with @gpcustoms I hit the fuel mpg reset before we left. On Lake Helen Osteen road in 4th gear going 45mph it was reading 70mpg.
On I-4 in 5th gear going 85mph it was reading 53 mpg.
 
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Went to the gun range last week with @gpcustoms I hit the fuel mpg reset before we left. On Lake Helen Osteen road in 4th gear going 45mph it was reading 70mpg.
On I-4 in 5th gear going 85mph it was reading 53 mpg.
I don't trust the read out to be honest :) How are you feeling miles per tank?
 

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To me it seems like I AM going longer in between fill ups.
 

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Nice! I will make sure to note my miles per tank with piggy back system (piggy haha) and after ECU flash!

If I didn't go 100mph+ (in theory) all the way to Deltona, I wouldn't have to stop and get gas to make it there....
 

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Once I get mine on I will start recording. Mine has been pretty stable around 24.3 to 25.2 mpg. Unfortunately I have to now make up for the difference in tire size in my calculations since the odometer is a little off. :(
 

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Once I get mine on I will start recording. Mine has been pretty stable around 24.3 to 25.2 mpg. Unfortunately I have to now make up for the difference in tire size in my calculations since the odometer is a little off. :(
I get around 22mpg if I take it easy (hrm wonder if my tires are messing with mine, kept 18 and 20, but went to 255/35 and 305/30)
 

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I think we need some hard data on this so starting later this week when im home from a business trip I am going to fill up and reset the MPG computer and trip computer. I will then document miles driven and do the math manually and check the computer math. My ECU has been reprogrammed for the new fuel map for the turbo. I will take pictures and compare the manual calculation to the computer MPG calculation. This will give us hard data to go off us and we can settle this once and for all :)
 

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To me it seems like I AM going longer in between fill ups.
With a properly designed and (street) tuned turbo system you should expect better MPG in normal driving ....... normal ..... but not anywhere near what some are reporting per their MPG meter. If your system includes larger injectors you can pretty much guarantee your meter is reading artificially high.

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This question can only be resolved by miles per tank. To get some of these numbers out there, I will be impressed if anyone gets over 320 miles per tank. That would be a huge improvement, and we can just use the blanket statement "Turbos are getting better fuel mileage"

That would be good enough for me.
 

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It'll be interesting to see what jim has to say with more driving. He drove from my place back to Utah and it sounded like the did the math on the fuel economy. I don't think he was using the onboard mpg calculator.
 

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I get around 22mpg if I take it easy (hrm wonder if my tires are messing with mine, kept 18 and 20, but went to 255/35 and 305/30)
Yes, you will be off.

Both of your diameters (35 and 30 series tires) will most likely be different in diameter that the stock (45 and 35 series). I say "most likely" because there are many variables - even the same manufacturer has different measured diameters for the same tire size between different tire models (see Nitto website) so by pure luck one could match the other. However, one Nitto 255/35/18 can be different than one Goodyear 255/35/18 so even knowing the stated measurement doesn't always give you the same diameter.

My mileage dropped from 25.2 to 23.2 by changing tire diameter from the 18/35 to 20/35. I am still getting 25.2 but the computer doesn't account for the new tire size. Everything points to a 5% change for me which looks about right in MPGs, Odometer, and speedometer readings.
 

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Yes, you will be off.

Both of your diameters (35 and 30 series tires) will most likely be different in diameter that the stock (45 and 35 series). I say "most likely" because there are many variables - even the same manufacturer has different measured diameters for the same tire size between different tire models (see Nitto website) so by pure luck one could match the other. However, one Nitto 255/35/18 can be different than one Goodyear 255/35/18 so even knowing the stated measurement doesn't always give you the same diameter.

My mileage dropped from 25.2 to 23.2 by changing tire diameter from the 18/35 to 20/35. I am still getting 25.2 but the computer doesn't account for the new tire size. Everything points to a 5% change for me which looks about right in MPGs, Odometer, and speedometer readings.
Tango, why dont you have a dealership flash your SS for the new wheel and tire sizes? They can flash for the SL and it should get you much closer.
 
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Yes, you will be off.

Both of your diameters (35 and 30 series tires) will most likely be different in diameter that the stock (45 and 35 series). I say "most likely" because there are many variables - even the same manufacturer has different measured diameters for the same tire size between different tire models (see Nitto website) so by pure luck one could match the other. However, one Nitto 255/35/18 can be different than one Goodyear 255/35/18 so even knowing the stated measurement doesn't always give you the same diameter.

My mileage dropped from 25.2 to 23.2 by changing tire diameter from the 18/35 to 20/35. I am still getting 25.2 but the computer doesn't account for the new tire size. Everything points to a 5% change for me which looks about right in MPGs, Odometer, and speedometer readings.
Ty sir!
 
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