greatskiiiier

iTrader: (10)

rollin just backed up my results, thank you tuner for that correction, at highway speeds the load on the engine is minimal compared to city driving, the car is at the same speed the whole time, no real strain on the motor

greatskiiiier

iTrader: (10)

this wasnt meant to turn into a debate just my observation... once i get a PM back from one of the 5 guys that are selling handheld programmers, ill be able to adjust the speedo and see how much of a diff it makes

02NBMWS6

iTrader: (22)

first off, an M6 with 3.42s @ 2300 rpm is either going 69 in 5th or 103 in 6th.

using your logic though, you'd be getting well over 40 mpg at over 125 mph with 2.0 gears. We all know that isnt right. Y would the same formula be right in this scenario just bc the inputs are somewhat less extreme?

99TransAmLS16Spd

iTrader: (8)

It's too late for that - I think you're missing the point some of us are trying to make. You needed to figure our your actual mpg when you had the 3.42s in there to get an accurate number.

Assuming your buddy's cavilier has a tripometer that is working, then your calculation is correct for you 4.10 gearing. This is because the wind resistance and engine rpm will remain the same as your first test. By updating the tune, you will essentially just be verifying your friend's car does have an accurate speedometer and trip.

But your 3.42 numbers will still be off. The only true way to calculate mpg for the 3.42s would have been to drive at 75mph at 1700rpm. But you are assuming that wind resistance for your car is the same at 90mph as it is at 75mph AND that your engine is just as fuel efficient at 2300rpms as it is at 1700rpms

02NBMWS6

iTrader: (22)

exactly. and that's incorrect

greatskiiiier

iTrader: (10)

ok so results are inconclustive /thread

BlackScreaminMachine

iTrader: (17)

What I can say is tuning the PCM to run lean from idle to 2.5k When not under WOT will greatly effect cruise MPG.

Also weight and stop and go driving habits factor in as well.

A "Lean" tune makes the biggest diff, and thats why you can see a c5 vette making 450-475rwhp getting mid to high 20 gas milage due to weight and tuning.

My heavy *** T/A with a 4.10 did about low 20's from a CT (Waterbury) to Montpelier VT run which is 220 one way approx. I cruised about 70-75 the whole way up. My mother who was in a 97 LeSabre likes to drive faster. I would have liked doing 65-70. A/C went on half way though, the windows were open on the 1st half.

landonew

I didn't think gears had anything to do with your speedo????

When I went to 411s I didn't need to reset the speedometer.

02NBMWS6

iTrader: (22)

wtf? Youre car didnt really get THAT much faster bc of the gears man...

jk, they definitely affect your speedo

HioSSilver

iTrader: (8)

I've attained my best mileage with 4.11. 29.1mpg and regularally aroung 28 hway and 20- 22 in town. I did'nt notice a change much either way.

01ssreda4

iTrader: (96)

i say this whole gear ratio/gas mileage issue can be observed rather easily. with an M6, lets do two test. one test ride at 70mph in 6th gear, lets pretend this is representative of factory 3.42s on the highway. now fill up, turn around and make the same trip and go the same speed/distance in 5th gear and lets pretend this is relative to the 4.10 ratio gearset. now which trip did you get better gas mileage on??? its all relative when you consider final or total drive ratios and the difference between 5th and 6th is very similar to a diff gear swap. also 5th is an easier load on the engine but at the expense of rpm, exactly like a gear swap.