Better mileage at 70 vs 65 ?

[Garak]

What I was getting at in my first post in this thread were some of the really high type overdrives we see trickling onto the market. I'd love to see the raw data on the cars in the test, and for that matter, every other car out there!

We could see lower mpg at 64 mph than 65 mph if the car actually shifted into its higher gear between those two speeds. Others have pointed out how some vehicles tend to linger in a lower gear than the actual top gear. The G will do that if one's in sport mode. Of course, "lingering" and staying put for a significant period of time to do a real fuel economy test of any sort are entirely different matters.

Did the Mercedes in the test have a reasonably advanced transmission? Mercedes would certainly have the incentive to make the vehicle as economical as possible in high speed driving (i.e. in Europe), yet not worry so much about speeds around the double nickel in North America with cheap gas and geriatric drivers.

 

[Vikas]

OK, science wins once again! With not going to 70+, the last tank averaged over 34mpg. With never exceeding 65, the early indications are at 37+ I was able to get the reading to go up as high as 38.5 on the cumulative gauge.

I am laughing at myself to be able to squeeze that mileage from the 270hp beach whale of that. All I am doing is going to work, I am no hurry to get there

I have essentially made it a game to increase the number on every trip. My objective has been no pressing of gas and pressing of brakes for the entire trip.

Am I building lots of carbon?

 

[surfstar]

My old Mazda MX6 would get great mileage on a pure hwy tank (road trips) at speeds of 75-80. For normal running around (beach, commuting, etc) I'd stay to 75. When Katrina hit and gas went to 4.75+/-, I would keep my max at 65. MPG increased 10%. Could save $5-6/tank.
Time is money, so it all depends on if I have the time to just cruise or need to get somewhere faster.

 

[Shaman]

Originally Posted By: eljefino
GM used to cheat and trigger a lean "highway mode" at a speed slightly above what the EPA certified them at. Maybe 56 mph?

Was back in the late 1980s when they used removable PROMs and of course OBD-I.

This lead to excess NOx and when they got busted they put the keibosh on that.


ADM LS cars would do it, and EFI Live brought it over to the US. It's complicated, but some would run 16:1 or more for short amounts of time.

 

[jimbrewer]

Originally Posted By: JOD
Originally Posted By: Vikas
Can engine efficiency at certain RPM overcome that drag?



Despite all you read on this thread, the answer is "it's incredibly unlikely".

Power requirements increase roughly with the cube of speed. Sure, there are differences in efficiency across the power band, but once you get over 40-50mph, there's now way those differences will be enough to overcome the additional power requirements unless something is wrong with your engine or transmission.

Either there are other variables at play, your measurement is imprecise, or there's something wrong with your car. Unlike the alternative universe that is BITOG, no one who accurately measures this stuff has ever discovered that increasing speeds over 45mph results in better fuel economy--ever. The key is the "accurately measuring" part, and it's not as easy as it sounds.


probably. Dad told me that his best tank in the old 1960s Lincoln was in West Texas going 80 plus mph. I think he told me he got 19 mpg. That would still be consuming over 4 gallons per hour in an engine about 460 ci. which seems plausible at least,

But yeah. its probably measurement error, and just tank to tank variation caused by tailwinds and unnoticed downhill slopes and the like.

 

[CBR.worm]

With my G35, I see very little MPG difference (2) between 75 and 100. It is very minor, below 50, my MPG drops quickly even in top gear.

My other car gets it best mileage between 45 and 55. At 55 I get 22
Mpg. 70 is 18mpg. 80 is 16.7. 90 is 15. Over 100 it drops fast. At 35 I get about 18.

My wife's BMW is pretty stable from 60 to 80mph (about 32mpg), but does significantly better than our other cars below 35 mph.