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Old 05-16-2019, 12:42 PM   #11 (permalink)
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Such a unicorn would need a really whack BSFC curve.

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Old 05-16-2019, 01:39 PM   #12 (permalink)
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Quote:
Originally Posted by Frank Lee View Post
Such a unicorn would need a really whack BSFC curve.
I agree, I think it is more a result driven by want. You want it to do better at the higher speed so the testing never gives the lower speed a real chance at success. More speed takes more power, more power takes more fuel, it's just physics. At speeds under 45 with different gearing and such where aero doesn't have as big of an effect I can see it, but once the car is in it's highest gear whatever that just off idle rpm is will be it's highest economy. If there was some problem with the tune or motor, again possible, maybe you are overcoming a vacuum leak or rich idle condition. Tuned for economy and in perfect mechanical condition, top gear, just off idle.
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Old 05-16-2019, 04:30 PM   #13 (permalink)
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Quote:
Originally Posted by Hersbird View Post
I agree, I think it is more a result driven by want. You want it to do better at the higher speed so the testing never gives the lower speed a real chance at success. More speed takes more power, more power takes more fuel, it's just physics. At speeds under 45 with different gearing and such where aero doesn't have as big of an effect I can see it, but once the car is in it's highest gear whatever that just off idle rpm is will be it's highest economy. If there was some problem with the tune or motor, again possible, maybe you are overcoming a vacuum leak or rich idle condition. Tuned for economy and in perfect mechanical condition, top gear, just off idle.


with TALL gearing, slow speeds arent going to work
below 45 in 6th gear, my GTO is below idle
the car works alot less at 1900rpm

I've done the same 300 mile trip from Silverdale, Wa to Cresswell, Oregon over 50 times in the same car
I was averaging 27-28mpg trying to keep my speeds down in the 60-65mph range, and was able to achieve 32-33mpg on the trips I could run @75mph
I'd call that noticable
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Old 05-16-2019, 04:33 PM   #14 (permalink)
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Quote:
Originally Posted by MetroMPG View Post
^ I've heard of such beasts, but have never seen it in any of the vehicles I've driven.

Comparison is always in top gear?

The car I've tested to closest to yours would probably be:





Thread: Tested: speed vs. MPG, 2008 Corvette Z06 (505 hp)
while the 33mpg @ 80 seems about right
my car loads up trying to go below 60 in 6th (cars behind me can smell unburnt fuel)
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Old 05-16-2019, 04:38 PM   #15 (permalink)
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Quote:
in 6th gear, my GTO is below idle

Did you leave something out of that tidbit? At a certain speed?
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Old 05-16-2019, 05:00 PM   #16 (permalink)
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Quote:
Originally Posted by MetroMPG View Post
Did you leave something out of that tidbit? At a certain speed?
oops, I did

it wa supposed to say at speeds below 45mph



also,
the GTO has a reasonably low CoD
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Old 05-16-2019, 06:34 PM   #17 (permalink)
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The Corvette posted above can do it at 820 rpm with a similar LS small block, you can too. If you aren't burning the fuel your A/F ratios are off for those RPMs. The factory working as designed wouldn't do that. You have leaking injectors or an aftermarket tune that loads extra fuel at low rpms in anticipation of a full throttle acceleration run, that is a performance tune. If you are willing to run aftermarket tunes, get a system that can load multiple tunes and even try the other way, a lean burn low rpm tune. Or just be honest and say, I really don't care what mpg it gets I want to go with the flow of traffic or even faster.
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Old 05-17-2019, 12:02 AM   #18 (permalink)
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In my coast down tests with bicycles on a street that drops 30 feet in 0.1 mile, I have measured the effects of drag reduction at speeds between 15 and 20 mph. A commuter bicycle and rider has roughly twice the Cd of a modern car. People value their time spent traveling as well as the fuel costs.

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Old 05-17-2019, 09:58 AM   #19 (permalink)
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Quote:
Originally Posted by Hersbird View Post
The Corvette posted above can do it at 820 rpm with a similar LS small block, you can too. If you aren't burning the fuel your A/F ratios are off for those RPMs. The factory working as designed wouldn't do that. You have leaking injectors or an aftermarket tune that loads extra fuel at low rpms in anticipation of a full throttle acceleration run, that is a performance tune. If you are willing to run aftermarket tunes, get a system that can load multiple tunes and even try the other way, a lean burn low rpm tune. Or just be honest and say, I really don't care what mpg it gets I want to go with the flow of traffic or even faster.
I can nolonger test this accurately
as I have an aftermarket (custom grind) cam, and an aggressive tune
my car also, wont get over 30mpg, at any speed (since the build)

but I can still get a solid 26-27 (which is still better than the (origional) EPA rating of 25mpg)
but I need to keep my speeds up around 70 (1700rpm)

I've had friends behind me say they can smell fuel when I'm at low rpm's
as well, it chugs below 60 or so
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Old 05-17-2019, 05:00 PM   #20 (permalink)
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Quote:
Originally Posted by Hersbird View Post
The Corvette posted above can do it at 820 rpm with a similar LS small block, you can too.

To be fair, that was on a dead-flat stretch of highway. Add hills / variable load, and the average MPG would suffer. Possibly dramatically.



My buddy still has that car, but unfortunately he doesn't regularly track fuel economy in anything he owns!

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