mileage test results, want 30+mpg?

bhuff30 · Jun 22, 2008

I was doing some datalogging on my 97GT using PCMSCAN from Palmer Performance. One of the items you can datalog is instant fuel economy, so I was playing around with this. I found a very flat streight road (ontop of a 2 mile long dam) and did some datalogging. Among the items I logged, were VSS (vehicle speed sensor) and the fuel mileage. I wanted to see at what speed you get the best mileage. All tests were done in 5th gear using the cruise control, and I varied in 10mph increments from 30 to 90 mph. Please note the speed listed is as recorded by the VSS (my stock mechanical speedo reads a little faster than the VSS)
MPH MPG
30 - 36.4
39 - 35.4
49 - 32.2
58 - 29.7
68 - 26.2
79 - 22.8
88 - 20.0
I believe these results to be very accurate. Two weeks ago, I took a 400 mile trip to ozark MO to pick up a transmission. The speed limit was 65, so I drove 70. On the way there, I got 26.5mpg, and the way back I got 26.0mpg. This is right on top of the data logged value of 26.2 today.
The car: 97GT, 151k miles, basically stock, just removed the air silencer (woot) and an off-road H-pipe. Stock 3.27 gears.
So if you were suckered into this thread by wanting 30mpg, and you are still reading... just drive 55mph.

Jbauer · Jun 22, 2008

You got a stock Non PI head GT to do 14.2 in a quartermile at only 96 MPH?

bhuff30 · Jun 22, 2008

haha, yeah but I'm sure the car hates me for it. I got the 60' down to 2.1X on street tires by slipping the clutch, usually from about 3400 if the track can hold it. Then, I power shift every gear at 5000 until I cross the stripe on the big end. I think when the weather gets nicer this fall, I'll bolt on the nittos from the 2.3 and see if I can get a 1.9 60'. It'd be pretty fun to run high 13s in what should be a 15s car.

Jbauer said:
You got a stock Non PI head GT to do 14.2 in a quartermile at only 96 MPH?

Jbauer · Jun 22, 2008

How the heck are you launching at 3500 RPM on street tires?
Heck, teach me a few pointers. I don't think even a PROFESSIONAL driver can get 13s out of a early sn95, but i'll be honestly pissed if you do lol

jprovence · Jun 22, 2008

Did any of you even read the thread, or are your penis's stuck on WOT in the quarter?

Mustang5L5 · Jun 22, 2008

Isn't that instantaneous MPG though, and not average?

A lot of vehicles will do better than 40MPG for brief times. My Lincoln Mark 8 has the MPG readout and i could get it into the 30's easily... but my average economy was never better than 26MPG.

Even the Infiniti i just test drove had it and i could get it up into the 40's on the highway for a few seconds

eliteJAE · Jun 22, 2008

yeah the GF has an 08 Cobalt, 5spd manual and it give the Inst. readouts for MPG.

at times it goes up to 95MPG and then drops back to 45MPG for a while

Stark77 · Jun 22, 2008

I got bored this afternoon, topped off the tank and did a 56 mile highway(one lap around jax/orange park) / 50 mile city cruise and achieved 25.5 MPG hwy(75mph) and 21.8 MPG city(45mph) granny driving. Best results I've ever seen. Just did an oil change last weekend a fuel filter change during the week. I even sprayed a bit'o'nitrous to totally embarass a Dodge Charger R/T.

COramprat · Jun 22, 2008

I gained nearly 2mpg slowing from 78 to 70 on the Interstate so I'm betting those numbers are fairly accurate.

Mustang5L5 · Jun 22, 2008

I found 65 to be my sweet spot. I once got 26MPG crusing 75 miles at 65 with the cruise on.

bhuff30 · Jun 22, 2008

These are instantaneous figures, but I averaged the results over about 30 seconds of steady state driving (cruise control). This is to maintain speed... not just coasting. Of course it goes rediculously high coasting, but that means nothing. I beleive these are realistic numbers, for my car anyway. I do have the tire pressure higher and my body style may be slightly more aerodynamic than the 99+.

My point is, I've heard a lot of people talk about getting better mileage at 80mph than they do at 55 and I always thought it was BS. I just did this test to prove to myself and others that lower speeds do get better mileage. Wind resistance is truely the dominating force, and I was surprised that speeds down to 30 even showed improved mileage. I expected there to be a peak around 55-60mph just because you are covering more ground and the engine should be operating more efficiently. But in FACT, the best mileage was at 30mph which is 1000 rpm in 5th gear.

But think about it. How many of you have ever tried driving 55, at steady state for a whole tank of gas? I honestly can't do it, and with speed limits at 65-75, you are likely to get run over or cause an accident. However, if you could, you'd get around 30mpg.

Mustang5L5 said:
Isn't that instantaneous MPG though, and not average?

A lot of vehicles will do better than 40MPG for brief times. My Lincoln Mark 8 has the MPG readout and i could get it into the 30's easily... but my average economy was never better than 26MPG.

Even the Infiniti i just test drove had it and i could get it up into the 40's on the highway for a few seconds

eliteJAE · Jun 22, 2008

thats odd to me that 30mph/1000RPM in 5th gear got that great of gas mileage, i alwasy thought boggin the motor like that would cause too much inefficiency lol

i guess i shouldn't be afraid of low RPM's

03TrueBlue · Jun 22, 2008

Less throttle means less fuel even if its chugging. I have noticed if I never let the rpms go over 2000 I get my best mileage.

rabidscoobie · Jun 23, 2008

I finally got my city milage and then my hwy milage and I didnt think its bad.I got 18.5mpg city only and then I went to dallas last weekend(400 mile round trip) and got a lil over 25mpg hwy only and 70-75mph.basically stock with 3.55 gears.

COramprat · Jun 23, 2008

03TrueBlue said:
Less throttle means less fuel even if its chugging. I have noticed if I never let the rpms go over 2000 I get my best mileage.

/\ /\ /\

Never had 4:10 to 1 gears.

streethorse · Jun 23, 2008

Last summer I went on a road trip about 200 miles 1 way.
Both there and back I got 26mpg. That was at 80mph with 3 people
and the AC running in 100 degree weather. I had a nice tailwind both ways.

Crzyhrse · Jun 23, 2008

I got 27mpg going 78mph on the Interstate on my recent roadtrip. The only time my mpg suffered was when I got caught in road construction and I was slowing down and speeding up. I was pretty impressed with my Mach's results.

urban96 · Jun 23, 2008

i wonder how gears affect those numbers

Pearl02 · Jun 23, 2008

bhuff30 said:
I was doing some datalogging on my 97GT using PCMSCAN from Palmer Performance. One of the items you can datalog is instant fuel economy, so I was playing around with this. I found a very flat streight road (ontop of a 2 mile long dam) and did some datalogging. Among the items I logged, were VSS (vehicle speed sensor) and the fuel mileage. I wanted to see at what speed you get the best mileage. All tests were done in 5th gear using the cruise control, and I varied in 10mph increments from 30 to 90 mph. Please note the speed listed is as recorded by the VSS (my stock mechanical speedo reads a little faster than the VSS)
MPH MPG
30 - 36.4
39 - 35.4
49 - 32.2
58 - 29.7
68 - 26.2
79 - 22.8
88 - 20.0
I believe these results to be very accurate. Two weeks ago, I took a 400 mile trip to ozark MO to pick up a transmission. The speed limit was 65, so I drove 70. On the way there, I got 26.5mpg, and the way back I got 26.0mpg. This is right on top of the data logged value of 26.2 today.
The car: 97GT, 151k miles, basically stock, just removed the air silencer (woot) and an off-road H-pipe. Stock 3.27 gears.
So if you were suckered into this thread by wanting 30mpg, and you are still reading... just drive 55mph.

I very interested in getting PCMSCAN. I read some on thier webpage. What all would I need to get going with this. Thanks. Pearl02.

bhuff30 · Jun 24, 2008

You'll need the software, a connection cable (and serial-USB adapter if needed) and a laptop. You can save the data logged as a comma seperated file, which can be easily openned and saved in Excel, which opens up a lot of possibities in data crunching.

It is an amazing tool for troubleshooting problems. However, I wish it had the ability to tune the computer.

Pearl02 said:
I very interested in getting PCMSCAN. I read some on thier webpage. What all would I need to get going with this. Thanks. Pearl02.

mileage test results, want 30+mpg?

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