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Discussion Starter #1
I just wanted to share how much I've improved my car for having no idea what I'm doing.

If you have a custom tune, I highly suggest that you check to see that the tire size field in your tuner is completed. Mine wasn't filled in, so I took a gamble and put in my 255/45r20 tires and boom; 0-60 time went from 4.5sec to 4.1 AND I now get 17.5mpg instead of 16.5.

Hope this is useful.
 

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your 0-60 and mpg are the same as the were before ... i.e. the car's performance hasn't changed - its just that the EVIC is showing revised outputs because they were wrong previously
 

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Discussion Starter #3
your 0-60 and mpg are the same as the were before ... i.e. the car's performance hasn't changed - its just that the EVIC is showing revised outputs because they were wrong previously
That makes sense for the mpg taking into account all of the factors that make that estimate up, but wouldn't the 0-60 be relatively accurate regardless of the tune settings? I mean, it's just a timer that stops when the speedo gets to 60...
 

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I'm not really sure if my tire sizes are actually programmed on my in-tune. I've entered them a few times but dont get an asterisk to show it's been change or entered. I've been meaning to borrow a Garmin GPS that shows MPH and compare with my speedometer.
 

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I'm not really sure if my tire sizes are actually programmed on my in-tune. I've entered them a few times but dont get an asterisk to show it's been change or entered. I've been meaning to borrow a Garmin GPS that shows MPH and compare with my speedometer.
If you have an iPhone or android, you can download a free GPS speedometer app. They're very accurate.
 

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That makes sense for the mpg taking into account all of the factors that make that estimate up, but wouldn't the 0-60 be relatively accurate regardless of the tune settings? I mean, it's just a timer that stops when the speedo gets to 60...
With the different size tire your speedo is incorrect. Chances are your EVIC initially had it programed as your 18" wheels, whereas youve got 20's now. Thats a larger wheel diameter (unless you have the same total dimension), which leads to an incorrect speedometer reading, along with incorrect milage (Distance, and thus MPG) reading.

For some reading this appears to be a good set of info for you: HowStuffWorks "Speedometer Calibration"

To elaborate: Larger tires leads to a lower speedometer reading (So your going faster than reported, this lines up with your reported quicker 0-60 time, your car is at 50 on the speedo, yet your really at say 60)
 

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Discussion Starter #8
With the different size tire your speedo is incorrect. Chances are your EVIC initially had it programed as your 18" wheels, whereas youve got 20's now. Thats a larger wheel diameter (unless you have the same total dimension), which leads to an incorrect speedometer reading, along with incorrect milage (Distance, and thus MPG) reading.

For some reading this appears to be a good set of info for you: HowStuffWorks "Speedometer Calibration"

To elaborate: Larger tires leads to a lower speedometer reading (So your going faster than reported, this lines up with your reported quicker 0-60 time, your car is at 50 on the speedo, yet your really at say 60)
I haven't changed the diameter, it's an SRT with the stock 20s. I can't imagine that diablotoona would make the custom tune for 18" regular 300 wheels, but you could be correct. I was just saying that the custom tune didn't have the wheel size filled in at all. This just suggests to me that he focused on the 6.1 engine fuel/spark/air/shift points and forgot about the tire size. I think that the difference between 4.5 seconds and 4.1 is way too close to blame on an inaccurate speedometer, but I understand what you're saying.
I'm definitely going to test the speedometer now though.
 

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4 tenths of a second is a decent chunk of time...a little looking around shows the '07 SRT8's 0-60 time at ~4.1s, very quick google though for that number


and ahh, my mistake, misread your info, missed the SRT8 , only saw 300c , DOH, no idea if the DS put it to 18's, could explain the difference, no idea im new to the 300c and tuners in general (still learning the Trinity I just go a week ago., So many options in it !)
 

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Let me start off by saying the evic timers are a 'guestimate' at best and not accurate to tenths of a second, so the 4/10's could have simply been differences in launch or even some spinning.... I've had flat 4's in my C but have also done a few 3.8's... while the 4's were matched very closely by my dashhawk the 3.8's actually showed a 4.2 and 4.5 on my dashhawk! I put it down to wheel spin... it's not an exact science. Your car most likely is a 4.1-4.5 second car as as most well launched SRT cars are, consistent...doubt it...but capable. As for the difference, sure it is possible that the difference in wheel size made a difference to your evic, your timer pulls from Speedo which is calibrated by the tuner, if the tuners off, so is your time. How much...who knows.. either way if it's calibrated now and you can get numbers in that range you are pulling strong. Diablo makes an amazing tuner, it's combination of shift improving characteristics, improved timing, fuel curves and reduction in KR is a great combo to make our cars perform well... a tenth or two in the quarter mile...sure... 4 tenths in 0-60...hmmmm...who knows...maybe!

Sent from AutoGuide.com Free App
 
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Discussion Starter #11
the 4/10's could have simply been differences in launch or even some spinning....
I thought of this immediately after I saw the 4.1 time, but dismissed the idea because I've never had that problem (except 1 sec 0-60 burnouts). I desperately need new tires, so this is very possible.

As for the difference, sure it is possible that the difference in wheel size made a difference to your evic, your timer pulls from Speedo which is calibrated by the tuner, if the tuners off, so is your time.
Same stock SRT 20" wheels, so it should be calibrated right. I'll double check.

Diablo makes an amazing tuner, it's combination of shift improving characteristics, improved timing, fuel curves and reduction in KR is a great combo to make our cars perform well... a tenth or two in the quarter mile...sure... 4 tenths in 0-60...hmmmm...who knows...maybe
Perfect explanation on what the tuner exactly does; I learned something new today.
 
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I do think you are probably doing 4.1's as well pal...Just think you may find you were also doing closer to that before than you may imagine! Lol...

Best way to tell, go find yourself a 4.5 second 'sports' car, find a traffic light, apply right foot and stomp his lights out... then you'll know she's a 4.1....hehehe!

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I do think you are probably doing 4.1's as well pal...Just think you may find you were also doing closer to that before than you may imagine! Lol...

Best way to tell, go find yourself a 4.5 second 'sports' car, find a traffic light, apply right foot and stomp his lights out... then you'll know she's a 4.1....hehehe!

Sent from AutoGuide.com Free App
I like that , I like that a lot :fing02: PAT
 
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