gas milage?
- Thread starter StangCrazy302Gt
- Start date
25thmustang
Mustang Master
How many gallons are you using. I know they have 15.4 gallon tanks, but when mines on E I usually end up filling 12-13 gallons tops. I assume going 350-450 miles you are running it basically bone dry. 450 miles is a LOT of miles to see in really any car, let alone a 5.0 Mustang. I will say I have seen 26-27 mpg on the highway (3.73s, the right speedo gear and 285/35/18 tires) with about 600-700 lbs of luggage, me (190 lbs) and my friend (230 lbs) coming back from SC, doing about 70-75 mph.
TRWXXA
Member
That's only a 0.08" difference between those tires. The change it would make in the speedometer reading is less than 0.5%. No speedometer gear is going to correct for that small a change. Most people are happy to have a speedometer that is within 5% accuracy.
Are you sure you have the correct speedometer gear?
Based on the chart where I bought it I do. What gear should I need with 3.55 gears? I think my speedo is like 5-8mph off, lol.
I'll verify that in the next few days, but I believe thats what I remember it being.
SteedaGT9150
Advanced Member
Here is the chart I used:
http://www.latemodelrestoration.com/buyersguide/speedo-gear.aspx
-Edit-
Just realized it stops at 3.55's on 90-93.
My '86 GT 'vert with AOD and stock 3.08's has gotten a best (so far) of 21 MPG and a worst of 17 MPG.
Frankenstang's notch (back when I had it) used to get somewhere around 19 MPG highway with 4.10's and a T-5. I'm guessing it was 19 MPG, though, simply because the speedo reads about 10 MPH high at 65 MPH (wrong speedo gear), and if you believe what it tells you, you'd be getting 24 MPG in that thing. Hell, it might actually be closer to 21 MPG for all I know...
Mileage = # of miles driven, divided by # of gallons put in to fill up.
Example: if your trip odometer says you went 150 miles, and you put in 7.5 gallons, then you got 20 MPG.
Didn't any of y'all pay attention in your freshman year math class in high school?
Frankenstang's notch (back when I had it) used to get somewhere around 19 MPG highway with 4.10's and a T-5. I'm guessing it was 19 MPG, though, simply because the speedo reads about 10 MPH high at 65 MPH (wrong speedo gear), and if you believe what it tells you, you'd be getting 24 MPG in that thing. Hell, it might actually be closer to 21 MPG for all I know...
Mileage = # of miles driven, divided by # of gallons put in to fill up.
Example: if your trip odometer says you went 150 miles, and you put in 7.5 gallons, then you got 20 MPG.
Didn't any of y'all pay attention in your freshman year math class in high school?
TRWXXA
Member
If you have the wrong speedo gear, you speedometer will be off by a percentage, not by a specific number of MPH. Thus, the higher the speed, the more miles per hour it will be off. If your speedo is consistently off by a specifice MPH throughout its range, you have another problem that a new speedo gear won't fix .Based on the chart where I bought it I do. What gear should I need with 3.55 gears? I think my speedo is like 5-8mph off, lol.
To figure out what speedometer driven gear you need, use this formula:
20.168114 / Tire Height X Axle Ratio X # of Drive Gear Teeth = # of Driven Gear Teeth
EXAMPLE: 20.168114 / 26" X 3.55 X 7 = 19.28 (19-tooth gear)
Since most tires will actually be a little smaller than their theoretical height, it's possible that you may need to get a driven gear with one more tooth than this formula or a speedometer gear calculator tells you you need. It's rare that you'll find a speedo gear/differential gear/tire size combination that will give you 0% error. The idea is to get the error as low as possible.
If you need to know how to figure out tire height, the formula is:
Tread Width X Aspect Ratio / 1270 + Wheel Diameter = Tire Height (in.)
EXAMPLE: (225/60R15) 225 X 60 / 1270 + 15 = 25.63"
That was the point... It's NOT what your trip odometer says, it has to be your ACTUAL miles traveled (odometer reading corrected for error).Mileage = # of miles driven, divided by # of gallons put in to fill up.
Example: if your trip odometer says you went 150 miles, and you put in 7.5 gallons, then you got 20 MPG.
Didn't any of y'all pay attention in your freshman year math class in high school?
The speedo gear I have in my car now is a 23 tooth I believe. I understand what you were saying about the speedo being off by a percentage, the numbers I was talking about was at highway speeds. Should of been more clear on that, I never looked down at the track to compare what my speedo was saying to my timeslip. Thanks for the help.
-Edit-
Based on this calculator, with a 23 tooth gear(which I have) my speedo will be off by -3%.
http://crt-performance.com/speedometers.htm
-Dave
TRWXXA
Member
With a 1992 AOD or 5-speed, a 23-tooth gear will give you about a -3% error -- which is pretty good. A 22-tooth gear (unfortunately, nonexistent) would give you a 1.5% error.
If you still think your speedo is off by 8 mph at highway speeds (is it fast or slow?), you may want to check the drive gear. Is it possible you have a 7-tooth drive gear (1983 - '89 5-speeds, and 1982 - '88 AODs) instead of an 8-tooth? That could account for an error of approximately -13%. A 20-tooth driven gear might be what you need.
TRWXXA
Member
How do you know your truck's speedo is correct? A vehicle's speedometer is allowed to be up to 10% too fast (it must not read too slow) from the factory.I'll have to get someone to drive my truck and pace me to see how much my speedo is off. I believe it reads faster than im actually going, I havent drove the car much in the last year.
The best method is to compare mile markers to the trip odometer. Go at least 10 miles.
The truck speedo is about dead on based on the speed I go through the traps vs what shows up on my timeslip at the track. I'll do the mile marker things as well just to see.
strtrcr50
New Member
What's gas milage?
+1. In the 1800 miles I put on my car this year, I didn't think to look/check.
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