8mpg?! REALLY?
Freshman User
Joined: Oct 2007
Posts: 33
Likes: 0
From: Foster, RI
Indicated speedo and odometer errors are going to be exponential. It also works the other way, larger tires=slower speedo readings and lower odometer readings. The faster you're going, the more the speedo/odo is going to be off. Kinda tough to calculate mileage that way...
HOW TO RECALIBRATE THE SPEEDOMETER ON 92-96 FORD F-SERIES AND BRONCO .: Articles
HOW TO RECALIBRATE THE SPEEDOMETER ON 92-96 FORD F-SERIES AND BRONCO .: Articles
What's changing with the larger tires over stock tires is the distance traveled per revolution of the tire, a larger tire will travel farther in one revolution. The speedometer calculates the speed by counting the number of revolutions of the tire in a second, via the tone ring and pick-up in the rear differential, and converts it into a mile per hour reading. The odometer simply counts the number of revolutions and calculates the distance traveled. The odometer calculation is not speed dependent so the faster you go will not affect its reading.
However, to get accurate speedometer and odometer readings you should recalibrate your PSOM to compensate for the different tire circumference, as described in the above link.
Posting Guru
Joined: Jan 2004
Posts: 2,403
Likes: 4
From: Charlestown, RI
The speedometer and odometer errors WILL NOT be exponential!
What's changing with the larger tires over stock tires is the distance traveled per revolution of the tire, a larger tire will travel farther in one revolution. The speedometer calculates the speed by counting the number of revolutions of the tire in a second, via the tone ring and pick-up in the rear differential, and converts it into a mile per hour reading. The odometer simply counts the number of revolutions and calculates the distance traveled. The odometer calculation is not speed dependent so the faster you go will not affect its reading.
However, to get accurate speedometer and odometer readings you should recalibrate your PSOM to compensate for the different tire circumference, as described in the above link.
What's changing with the larger tires over stock tires is the distance traveled per revolution of the tire, a larger tire will travel farther in one revolution. The speedometer calculates the speed by counting the number of revolutions of the tire in a second, via the tone ring and pick-up in the rear differential, and converts it into a mile per hour reading. The odometer simply counts the number of revolutions and calculates the distance traveled. The odometer calculation is not speed dependent so the faster you go will not affect its reading.
However, to get accurate speedometer and odometer readings you should recalibrate your PSOM to compensate for the different tire circumference, as described in the above link.
Elder User
Joined: Nov 2006
Posts: 973
Likes: 2
From: Texas
easiest way to add for incorrect speedo calibration is a percentage.
I have a spreadsheet set up for my mileage too! Works great.
The only time my 300 got below 10 mpg was pulling a giant wooden box down the highway at 70mph. If its getting under 10mpg then there is some other issue. Even when i am trying to burn gas i dont get that low.
You also have to take into account idle time, and warm up time, which can make a big difference.
I have a spreadsheet set up for my mileage too! Works great.
The only time my 300 got below 10 mpg was pulling a giant wooden box down the highway at 70mph. If its getting under 10mpg then there is some other issue. Even when i am trying to burn gas i dont get that low.
You also have to take into account idle time, and warm up time, which can make a big difference.
Junior User
Joined: Dec 2009
Posts: 81
Likes: 0
It doesnt make sense to that the 300 would get better mileage than the 302. They are basically the same size engine, with the 300 having bigger pistons, which I learned, always get worse mileage than smaller piston engines? Correct me If im wrong but, that makes sense to me.
My 302 and 5spd gets 14-15hwy and 10 in town.
My 302 and 5spd gets 14-15hwy and 10 in town.
Elder User
Joined: Nov 2006
Posts: 973
Likes: 2
From: Texas
300 pistons are close to the same size, but it does have a much longer stroke. The reason the 300 or any 6cyl engine get better gas mileage is because it uses more of each individual combustion. It produces the same power using less fuel. The only downside is that it make power much more slowly.
A 6 cylinder engine divides each rotation of the engine into 6 parts. So each cylinder rotates the crankshaft 60 degrees. A v8 divides each rotation into 45 degrees. In the 60 degrees that the cylinder is rotating the crank, it uses more of the energy created by the burning fuel before the next cylinder fires, where as a v8 has less time to use that remain energy before the next cylinder fires.
I hope that kinda makes sense, its kinda late for me, and things dont always come out as clearly as they seem in my head.
A 6 cylinder engine divides each rotation of the engine into 6 parts. So each cylinder rotates the crankshaft 60 degrees. A v8 divides each rotation into 45 degrees. In the 60 degrees that the cylinder is rotating the crank, it uses more of the energy created by the burning fuel before the next cylinder fires, where as a v8 has less time to use that remain energy before the next cylinder fires.
I hope that kinda makes sense, its kinda late for me, and things dont always come out as clearly as they seem in my head.
Posting Guru
Joined: Nov 2008
Posts: 1,183
Likes: 0
From: Pennsylvania Wilds
Also, an I6 is in perfect mechanical balance, and has fewer moving parts, which should equate to less inertia to overcome when those moving parts change direction and/or speed, and less friction.
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Post Fiend
Joined: Apr 2004
Posts: 6,473
Likes: 4
From: Lafayette, IN
300 pistons are close to the same size, but it does have a much longer stroke. The reason the 300 or any 6cyl engine get better gas mileage is because it uses more of each individual combustion. It produces the same power using less fuel. The only downside is that it make power much more slowly.
A 6 cylinder engine divides each rotation of the engine into 6 parts. So each cylinder rotates the crankshaft 60 degrees. A v8 divides each rotation into 45 degrees. In the 60 degrees that the cylinder is rotating the crank, it uses more of the energy created by the burning fuel before the next cylinder fires, where as a v8 has less time to use that remain energy before the next cylinder fires.
I hope that kinda makes sense, its kinda late for me, and things dont always come out as clearly as they seem in my head.
A 6 cylinder engine divides each rotation of the engine into 6 parts. So each cylinder rotates the crankshaft 60 degrees. A v8 divides each rotation into 45 degrees. In the 60 degrees that the cylinder is rotating the crank, it uses more of the energy created by the burning fuel before the next cylinder fires, where as a v8 has less time to use that remain energy before the next cylinder fires.
I hope that kinda makes sense, its kinda late for me, and things dont always come out as clearly as they seem in my head.
Jason
Posting Guru
Joined: Jun 2003
Posts: 2,314
Likes: 0
From: southwest michigan
I also do the write mileage on the back of the receipt and spreadsheet thing. It works like a charm.
http://jandscoatings.com/temp/MPG2.htm
if it's the worst one out of all of them except the 351, doesn't that only leave the 302 to be worse than? 
http://jandscoatings.com/temp/MPG2.htm
Senior User
Joined: Aug 2009
Posts: 382
Likes: 0
From: Delta,UT
mind sending me a copy of the spreadsheet you use? bigmacmonday@gmail.com
Senior User
Joined: Jul 2009
Posts: 201
Likes: 0
97 F250HD 4x4 x-cab longbox. 460 auto, 4.10s. 18mpg highway hauling quad and reasonably heavy right foot. Mind you I was LUCKY to get 10mpg highway empty when I got it. To date I haven't even pulled a spark plug out of it. Simply put, you have to go through it and find what's not working... sensor, plugs, whatever and fix it, then start going through the factory junk and fix it. Get the air and fuel in, get it burnt, and get rid of it. Free up the exhaust, make sure the fuel system is half decent, decent spark is a must, and... in my opinion, the factory ford intake system is garbage.
I gained most of my mileage from a K&N and basically cutting the bottom of the air box off. More warm air is better than less cold air. I always wanted to modify the hoses from the throttle body to the filter, but haven't got there yet.
I gained most of my mileage from a K&N and basically cutting the bottom of the air box off. More warm air is better than less cold air. I always wanted to modify the hoses from the throttle body to the filter, but haven't got there yet.
