Ok Got anouther question for you guys,
I had my gears changed this week from 3:55s to 4:56 due to my tire change.It helped tremendously with the power and its no longer shifting in and out of overdrive the things I did notice was my speedometer is off about 10 mph,,which I expected the other thing is my rpms are higher when im at cruising speed on the highway. At 60 my rpms were normally at 1200 now at 60 Im at about 1900/2000 is this normal? and what causes this? This gear thing is all kind of new to me so any info will be greatly appreciated.

Thanks again,,,,

 

When you had the gears changed, did you have the computer re-flashed for the new gears?

4.56 seems a bit drastic, you must be running pretty tall tires.

 

Those rpms sound about right, like what superranger said you must be running a pretty tall tire with 4.56. I went from 3.55 to 4.10 with 33" tires and rpm's are 2000 @ 65mph.

 

Thanks,,
Im running 36" tires. I didnt have anything done to the computer though? Is that just a matter of disconnecting the battery?
Thanks again for the quick response.

 

Well, let me help explain the whole gear thing. 4.56 is the number of times the rear end multiplies torque coming from the transmission. If you have 100 lb/ft of torque coming thru the transmission, it will put out 456 lb/ft to the axles. With 3.55's it would be 355. Did you know about the lever and pulley effect in physics? 4.56's aid with acceleration, but in turn your engine revs will be higher. Better acceleration, but lower top speed. It's like the pulley effect. In order to spin your rear axle 1 rotation, the gear inside your differential must turn 4.56 times. Thats why, at the same speed, your engine revs will be higher with shorter gears. You will need to, or at least *should*, have your speedometer re-calibrated. With your experience, I'd suggest having a professional do this. It's not very difficult, nearly any shop you take it to will be able to do this for a very small charge, etc. But it does involve electronics in cars which most people, even very experienced people, like to leave to the pros. This should be done from the speedo box on your rear axle, or at least that's how its done on cars. Not sure about ford trucks, I'm new to them as well. Re-flashing your ECU (engine control unit, the thing that controls almost everything about a fuel injected engine), is a process where you tell it the truck now has 4.56 gears instead of 3.55's. Not sure if it even needs to be done, if it would affect anything the engine does (about 90% sure it wouldn't), but again, take it to a shop. Have your speedo recalibrated and ask the tech if you need your ECU reflashed.

 

Personally I would spring for a tuner, something like a Diablo Predator off this site.

It will allow you to adjust the computer for the gears and tires you have, read codes, and much more.

Not to mention it will give your motor a bit more pep!

 

Thanks guys I really do appreciate all this info! At least now I have a better understanding of whats going on!!

 

like superranger said, if you buy a tuner, you can set it to your tire size and new gears, it will correct the shift point speedo and give you some extra ponies too...