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Discussion Starter #1 (Edited)
I've been primarily relying on the EVIC to give somewhat accurate mileage information. But if it's accurate at all, then I am correct in what I've found so far...

Stock tune, I found the absolute best MPG I could get is about 34 MPG on a flat road with cruise at 55-60 MPH. This would literally read out 34 MPG (small fluctuation for change in grade) for miles and miles, so I am inclined to believe it to be true.

91 tune, using BP fuel at the same station and pump for a few days, by doing my best-guess at a 50:50 ratio of Silver (89) and Amoco Ultimate (93), I could get a max of 27 MPG in the exact same scenario of cruise and flat road for miles. I didn't notice a big boost in the tune, nor did my 0-60 numbers (then again I'm still learning how to launch). The shift firmness also seemed sporadic - sometimes I could tell it was firm, and other times it felt stock. My mileage averaged (calculated) 20 MPG for 230 miles. Granted, I did have a night where I was flooring it after every stop for about 10 miles and hitting up to 100 MPH.

Switched to the stock tune, but kept some adjustable parameters such as shift firmness and top speed increase. I can feel the shift firmness all the time now. I had half a tank of the 91 mix, and put in Silver (89) again for about 10.5 gallons to fill it up, so I'd say it's at about 90 octane now. Anyway, my mileage has gone back up according to the EVIC. Last night on a trip from my home to Dayton, and back... cruise on the highway, set to 60 MPH and left alone (minus about 3 miles of city driving), I averaged this for 72 mile round trip.



Am I crazy? Is my EVIC broken? Or are these cars actually pretty dang fuel-efficient provided you let it do it's thing... but I've never seen anyone talk about numbers here that I am. So what gives?! I can't believe the 91 tune wrecked my MPG like that, but I may try the 93 tune for giggles. I don't want to spend that much in fuel though for a small "gain", and am really beginning to wonder if this tuner was even worth the money.
 

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People will say that the EVIC isn't completely accurate. It may be 1 or 2 mpg off at times, but honestly that's what I go by to determine my mileage. These cars are actually very efficient stock. My 2011 R/T would average over 28 miles per gallon on a long highway drive with the factory tune. Never bought a Diablosport for it, but I doubt it would have done much of anything with the MPG.

Did you leave MDS enabled? Also, i'm not sure if the diablo has the "CAI tune" option, but those dump in extra fuel if you choose to use that tune. If you didn't choose either to disable MDS or a CAI tune, then I'm really not sure why you're mileage is so down with the tune.
 

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Discussion Starter #3
I re-tuned the 91 again to specifically make sure MDS was enabled. No change. Also, the 11+ models have no CAI tune option. Only stock, 91, and 93.
 

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Ddaddy posted some info in another thread showing how low octane fuels produce more energy per gallon. Your results are consistent with that.

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Discussion Starter #5
Ddaddy posted some info in another thread showing how low octane fuels produce more energy per gallon. Your results are consistent with that.

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That seems like quite a large difference! I thought the flip side to this was a higher compression ratio allowing for more power? Would that only help in situations such as WOT? If so, screw the performance tunes and I'll keep my cash. She is plenty fast without them!
 

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Another thing to remember...generally speaking, and I mean GENERALLY, more power/performance = poorer fuel economy. That is still a relatively large range, usually you see a 1-3 mpg decrease give or take. That's where what the guys above information comes into play.


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Yes, higher octane allows for higher compression but a Diablo time does not modify compression one iota. Compression does not change electronically. So, higher octane can result in lower fuel efficiency.
 

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The OP should do some data logging and see how many degrees of ST/LT knock he's getting. The diablo canned tunes tend to have the timing advanced too much.


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Discussion Starter #9
The OP should do some data logging and see how many degrees of ST/LT knock he's getting. The diablo canned tunes tend to have the timing advanced too much.


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I did an initial datalog that was a few minutes long, mostly testing for knock at WOT. Zero LT knock throughout, with sporadic ST knock at high RPM's. It rarely happened, and only once did it reach as high as 4 degrees. The rest were 1-2. I didn't see any knock at cruising speeds, but like I said this was a very limited run.
 

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Nice you're on the ball brother! Those knock readings are excellent. Ideally you want zero LT knock (which you do) and less than 6 degrees ST knock at WOT. You only will see knock at WOT. Since we have summer fuel now the tune may be responding better.

When I first tuned my car I noticed a slight decrease in MPGs and when I went for a custom tune I notice a larger decrease in MPGs. I asked a similar question to yours and was told greater performance leads to poorer fuel economy...which makes sense by all accounts. Ideally you want fuel economy and power but sadly those two don't go hand in hand, generally. Try a few different gas stations and see what works best. For me and where I live I will only fill up with Shell or Chevron gas...that's the only decent stuff we have out here.


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Ddaddy posted some info in another thread showing how low octane fuels produce more energy per gallon. Your results are consistent with that.

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Not trying to bust your chops here, but why is it that my Dart gets more miles per gallon using 93 (91 or higher recommended by manufacturer) than 87? If the theory you stated was true (which I'm not suggesting it isn't), wouldn't I get more miles out of a tank using 87?

My Charger with the 5.7 also got much better mileage using the suggested 89 octane as opposed to 87.
 

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Not trying to bust your chops here, but why is it that my Dart gets more miles per gallon using 93 (91 or higher recommended by manufacturer) than 87? If the theory you stated was true (which I'm not suggesting it isn't), wouldn't I get more miles out of a tank using 87?

My Charger with the 5.7 also got much better mileage using the suggested 89 octane as opposed to 87.
Not busting my chops at all. I was referencing a post by Ddaddy. But, if you're using under the recommended octane, I'd guess it's because the engine can't adjust itself well enough. You would have to compare recommended and higher. Again, a guess.
 

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Not sure what tunes come with the Trinity but if there is a 93Oct vs a 93OctCAI, you may want to switch between the two and see which works better.
 

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Positive results

I use the intune, using 93 octane gas and wanted to figure out my gas milage once a saw this thread a while back. I drove around 320 miles, majority highway and after, I did the calculations and found I got 24.8 mpg.

I think this is good results because when I did a test to see how my gas mileage was when I first bought the car, I calculated I got 19.6 mpg. This trip was about 240 miles and it was mainly highway driving as well. The previous trip I was cognitive of how fast I accelerated and I didn't push her too hard.

With those numbers, IMO, it confirms that the intune "CAN" give you an increase in mpg "IF" you drive conservatively. Scientifically it makes sense too because the intune can give you better mpg, if you drive more conservatively, or more horse power, if you want that, by driving harder. The intune doesn't just pull the horse power out of its electronic gizmo's tho :biggrinjester: it reprograms the engine to get the power by giving the combustion chambers more gas. Thus if you drive hard and give your engine more gas, it will be less efficient.
 

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Not trying to bust your chops here, but why is it that my Dart gets more miles per gallon using 93 (91 or higher recommended by manufacturer) than 87? If the theory you stated was true (which I'm not suggesting it isn't), wouldn't I get more miles out of a tank using 87?

My Charger with the 5.7 also got much better mileage using the suggested 89 octane as opposed to 87.
Some 2011's seem to be factory tuned to 91, so u will get the best mileage for it
most 5.7s are tuned to 89, utilizing the compression and octane best without knock thus better performance and mileage
as for the dart, u may either have the one with turbo
and Dodge has been known to use engines with a compression that gets the most out of one specific octane and downtuning it, so in closed loop operation(non WOT) the engine will use the fuel you put in as efficiently as it can as long as there is no knock. Once you go WOT, the tuning kicks in and fuel maps are run as programmed without paying much attention to knock...
the Dodge Intrepid RT was one of these wierd cars, where the Chrysler version with the same engine would make 10hp more during WOT, the Intrepid was downtuned, however, when you werent in WOT it ran better on 89 octane than the called for 87
 

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I use the intune, using 93 octane gas and wanted to figure out my gas milage once a saw this thread a while back. I drove around 320 miles, majority highway and after, I did the calculations and found I got 24.8 mpg.

I think this is good results because when I did a test to see how my gas mileage was when I first bought the car, I calculated I got 19.6 mpg. This trip was about 240 miles and it was mainly highway driving as well. The previous trip I was cognitive of how fast I accelerated and I didn't push her too hard.

With those numbers, IMO, it confirms that the intune "CAN" give you an increase in mpg "IF" you drive conservatively. Scientifically it makes sense too because the intune can give you better mpg, if you drive more conservatively, or more horse power, if you want that, by driving harder. The intune doesn't just pull the horse power out of its electronic gizmo's tho :biggrinjester: it reprograms the engine to get the power by giving the combustion chambers more gas. Thus if you drive hard and give your engine more gas, it will be less efficient.
I havent seen anywhere near my original MPG with any performance tune, however, since putting the bolt ons to allow my car to breathe better, mpg's went up. So it canceled each other out for the most part, but then the tune adds more fuel and my fuel econ went lower.
Thus, I have installed the DS factory tune, adjusted the few parameters for tires and throttle, and my fuel economy shot up 5-7 mpgs.
 

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Discussion Starter #17
I retried the 91 tune and am using 93 gas from Speedway (not sure if I want to keep getting there - it's a high volume station and cheap, but not sure about quality). I may have gotten my best 0-60 time yet, and my MPG is much better... MAYBE 1 MPG less than stock, but I need to test more.
 

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Not trying to bust your chops here, but why is it that my Dart gets more miles per gallon using 93 (91 or higher recommended by manufacturer) than 87? If the theory you stated was true (which I'm not suggesting it isn't), wouldn't I get more miles out of a tank using 87?

My Charger with the 5.7 also got much better mileage using the suggested 89 octane as opposed to 87.
Over how many tanks of each did you calculate gas mileage? Also, if you crossed over between winter and summer gas it can be an issue.

there are less Btu's of energy in higher octane fuel than lower octane fuel. With all other things remaining constant, you will get lower gas mileage. I'd be shocked if the Dart engine would stretch the tune to account of higher octane fuel.

Fuelly.com is a great resource for tracking actual fuel economy.
 

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Not trying to bust your chops here, but why is it that my Dart gets more miles per gallon using 93 (91 or higher recommended by manufacturer) than 87? If the theory you stated was true (which I'm not suggesting it isn't), wouldn't I get more miles out of a tank using 87?

My Charger with the 5.7 also got much better mileage using the suggested 89 octane as opposed to 87.
If you are running lower than the recommended octane for the engine design, you are going to get knock which causes the engine PCM to pull the timing and destroys your fuel economy.

However, that doesn't change the fact that lower octane produces more energy per unit volume than higher octane. It just doesn't work in a higher compression engine which causes the fuel to detonate under compression (knock) robbing the engine of power.

The rule is that you should run the lowest octane your engine is designed for to get the most power from it.
 

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If you are running lower than the recommended octane for the engine design, you are going to get knock which causes the engine PCM to pull the timing and destroys your fuel economy.

However, that doesn't change the fact that lower octane produces more energy per unit volume than higher octane. It just doesn't work in a higher compression engine which causes the fuel to detonate under compression (knock) robbing the engine of power.

The rule is that you should run the lowest octane your engine is designed for to get the most power from it.

Just throwing this out there for discussion purposes. If your running a 91 tune and your adding Aces IV to the tank your Octane level would be comparable to say 100. Based on what you said, that would not be good for power correct? However, Ive been testing Aces IV with my 91 tune running 91 fuel and so far it seems to run slightly better with a bit more power. But now I'm wondering if I should drop down to 89 octane with the Aces which in theory would produce a closer octane match to the tune. Thus more power.
 
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