4 speed to 5 speed?

Sure it would help, but I don't know that it would help that much. I wouldn't think the cost of the change would be recovered for a long time. If you're having trouble with the 4 speed, then by all means go with a 5 when you replace it. Otherwise, you're probably wasting your time and money.

CJB

Either a 4 speed or a 5sp with a OD in it may help some but it may not if it reduces RPM to the point that engine is working to hard to pull it.

----------------- The SnoMan

yes it will help. question is going to be how much will it cost to do the conversion vrs how much you will save in fuel. If your four spd manaul is a top loader, in the late 70's and early 80's ford used a top load four speed over drive, ie a three speed plus an over drive in the F150, and it came behind the 300 cid six banger. It will be a drop in replacement if you can find one. I would estimate from past experiance driving the 4 sp over drive, you will look at about an 800 rpm drop at 55 mph. I think I remember seeing them in some E 150 vans as well. Its a very stout gear box.

Whitelightning

Not sure where you are getting you "yes it will help" because it is not always cut and dried. Secondly, not sure where you get the 800 RPM drop either because that is not going to happen unless you are turning about 3000 RPM at 55 mph. Generally manual trannies have a OD in the range of .8 to .75 or there about which means you will see a 20 to 25% RPM drop so if you are turning 2500 RPM at 60, you will be turning

1900 to 2000 RPM afterwards.

If you want to play with the numbers, use the link below

SnoMan

I don't need to play with the numbers. I know that 3rd was a 1:1 ratio, and when I stuck it in 4rth the rpm dropped 800 rpm. The speed limit in Texas at the time was double nickels, 55 mph and it put the rpm at 1700.. Your right on one aspect though, empty the truck could pull all right, but when there were

2-3 cars on the trailer behind it, OD was a no go at 55. I drove the beast, as we called it because the boss had stuck 3/4 ton springs under it and added overloads to boot and it was a rough as ride, from Harker Heights Tx to Waco once a week to the car auctions for 14 months..

Whitelightning

You do need to do the numbers because math does not lie but tachs sure can.

----------------- The SnoMan