BJM

iTrader: (1)

Rather than ressurect that "5th or 6th gear on highway??" thread again. I thought I would post this separately. I did a bunch of data logging on my car to help me choose a new rear gear.

So if you prefer to drive in 5th on the highway, you should at least know how much extra fuel you are using. Also for those convertible owners you can see how much having your roof down affects your mileage. These numbers were each done by driving for a minimum of a mile at a fixed speed and collecting data in both directions. For speeds above 60 mph, the distance was approximately 4 miles each way.

Overall at 75 mph using 5th gear instead of 6th uses 14% more fuel (-3.75 mpg).
Also at 75 mph, dropping the roof uses 5% more fuel (-1.25 mpg).

chris2000ss

iTrader: (9)

nice info !! I always run 6th on the highway

tici

iTrader: (1)

Interesting info, thanks!
I'm surprised about the difference with/without roof: I haven't checked it properly, but I was sure it wouldn't make a difference

How have you checked the consumption?
I once did it using the MAF reading (G/sec), vehicle speed and AFR (assumed constant at 14.7).

BJM

iTrader: (1)

I measured basically as you stated.

I use the commanded AFR, the MAF, and the short and long term fuel trims to work out g/s of fuel. Then I can work out instantaneous mileage. Over several hundred samples I count up cumulative fuel used and divide by the distance traveld in that interval. That way I can average over many sample points easily.

bayer-z28

iTrader: (14)

I drove from CT to NM I used 6th. Doing about 63~ish, turning 1500RPM I noticed thta the car was getting great mileage. I figured about 25MPG. I'll have to try a constant 75 next time.

Good research!...

tici

iTrader: (1)

Good point this of correcting the values using LTFT + STFT! And hopefully you are using the stock MAF table

Are those values something you calculate after the test or are you able to have them while driving?

It would be interesting too, to see if using the cruise contol helps you to save some fuel. Over here we pay now 1.65 Swiss Francs per liter or US$ per Gallon... that's why I'm interested!
I can imagine that our feelings aren't fine enought and we continously accelerate-decelerate. What causes more consumption

BJM

iTrader: (1)

If I worked it out right you are paying $1.83 CAD/litre where I am paying about 0.90 /litre for 91 octane. No wonder you are interested.

I currently post-process my data but I could define a custom PID to do it instantly. I would still have to do the averaging myself though.

The specific MAF table or speed-density calculations for air flow don't really matter if you use the fuel trims, a mis-adjusted table gets corrected out. You do have to believe that the O2 is doing its job however.

I use cruise quite a bit myself to keep mysefl from speeding. I have never tried to prove it but conventional wisdom says it will save you gas using it. Since any over-speed above your intended speed is met with a non-linearly increasing wheel and wind drag, you are disproportionally penalized by going too fast. Cruise is good here because it really never allows that to happen.

slayer_taunu

iTrader: (3)

thats excellent! i thought it was very interesting that you did an analysis on having the convertable top down... would love to see data on t-tops as well!