it's very simple, eliminate drag......increase mpg. no tuners etc.

 

Hi,
Did you change tire/wheel size too? I thought that the speedo wasn't effected by axle ratio changes?

Bob C

 

Changing the rear end ration will definitly have an effect on the speedo.

 

Really? I had read on this forum and others that the computer calculates speed by tire revolutions... so only wheel/tire size changes effect the speedometer?

edit: I just found one of the threads that states this...

ratio change??? - Diesel Forum - The Diesel Stop.com

Some guy there switched from 4.56 to 3.73 and the speedometer didn't change at all.

Thanks!
Bob C

 

I know for a fact...I crawled under and looked...that the speedo sensor is on the tailshaft of the transmission.

Looking at the link you posted it is obvious that they have no idea what they are talking about...the guy that stated 4.56s didn't affect his speedo also put on 38" tires. Adding the 38s would have made his speedo read low then adding the 4.56 gears would have countered thatlow reading. So the end result is the speedo is correct, but only because he increased tire size with the rear change.

 

This post exactly illustrates my point. The tire change made the speedo read low and the gear change brought it back up. He says they are correct that changing the rear has no effect then goes and shows proof that it does.

BTW, I have never seen a vehicle that took the reading off of the rearend like they are talking about...I'm sure they are out there, but not on the Ford Superduty...

 

On the top grill side openings - did you tape flush with the front of the grill (taping to the chrome), or did you tape up down in the opening on top of the plastic grill work?

 

Thanks for the info.

Geez I wish we bought a 3.55 LS from the get go. Ours is a job 1 3.73 open diff.

Bob C

 

editops double post

 

BTW, I have never seen a vehicle that took the reading off of the rearend like they are talking about...I'm sure they are out there, but not on the Ford Superduty...[/QUOTE]

All F350 and F250 have the speed sensor on top of the rear end, all the way back to 1992 that I know of. Not sure about the F450.

 

Taped up the side grill openings and the tow hook openings. Went on a 2 1/2 hour trip hauling a 4,000 lb camper (half interstate, half country roads). Ran about 9.9 mpg. Noticed the fan came on a couple times when climbing a moderate hill which was unusual. Took the tape off for the trip back and got 10.4. A little more downhill on the trip back.

The tape might make a difference on unloaded highway speeds, but since I rarely run unloaded, its staying off.

I put a grill cover on in winter, and didn't get any higher mileage then either.