I have a 92 F-150 with a 5.0L and from what I can tell a 3.55 rear end. I am not real worried about mt towing capacity as I don't do much of that. I was wanting to possibly do some rear end swapping out to maybe increase the gas mileage a bit. I know there is a 2.73 ratio that was used on 4.9L F-150s with 5 sp trannys. Would this be a good swap to do or not? If not, I wonder if the 3.08 rear end would be worth the swap or not. Would appreciate any thoughts anybody has.
Thanks,
Matt
I forgot to add I have a E40D tranny.
Ok, here's what I've come up with. If you really have an E4OD, which would surprise me, it has an overdrive ratio of .71/1. You don't say whether or not you have a 4x4 or 4x2, but I've done my calculations assuming you have a
4x2. If you do, you almost certainly have 235/75R15 tires, or at least those were on it from the factory. If so, then at 65 MPH, the engine is turning 1906RPM. Changing to a 3.08 would make the RPM at 65 1654, which is not a lot of reduction in rpm, but would add noticeable load to the engine.Reducing the axle ratio would not be wise, IMHO. Your truck is not light, and it has a lot of frontal area. If you live in the mountains, it's an even worse idea to reduce the axle ratio, because you'll constantly be hunting in and out of OD and lockup, and will shorten the life of your transmission.
If you have an AOD-E/4R70W transmission, your OD ratio is .67/1, and that makes your RPM at 65 1799. You really don't wanna go lower than that at all. Plus, all those numbers are skewed (even lower rpm) if your tires are larger than 235/75R15.
I once had a GMC conversion van with a 2.73 axle, 235/75R15's and a TH700R4 and 350 in it. The van could barely stay in OD on flat ground with no wind. Even a headwind and it would have to shift to 3rd, let alone a grade. The original owner had 3 transmissions in it in 75k miles because of the constant shifting.
CJB
Yea, but wouldn't he have a top speed of about 599mph?
Spdloader
The problem with the 5.0L is that it needs a few more revs than a 300 six to get to an efficient operating range. The
3.55 is probably the best economy gear for the 5.0L with an E4OD if your are not working it with a load or a tow. If I had it to do over again, I would go for the 3.73 with the better performance and minimal hit on fuel economy. This is especially true where the speeds are 70+ and the 5.0 could use a few more RPM for more torque so it doesn't work it's little ass off. If you are towing heavy, a 4.10 won't hurt it much at all.Lugnut
The E4OD was definitely an option behind the 5.0L and is what I spec'd in the ones I have had. The AOD/4R70W is/was not a truck transmission in my estimation. I have laways had the 3.55 gears with this combination because I could never find a 3.73 or 4.10 without ordering it. At 70+ MPH the 5.0L definitely needs more gear to let it breath a bit. If you set the cruise at 80 which is common in this part of the world, it will hunt in and out of OD with any grade or headwind. If I kill the OD under these conditions, I only lose a mile or so per gallon but, that is spinning 40% or so faster which is more than even a 4.10 gear would increase it. My current setup is a SC but, the experience is pretty much the same as was the case with the reg cabs before. I just can't believe there is enough difference in fuel economy to make it worth the hit on perfromance.
Lugnut
Why would that surprise you! I have the same year truck with the same engine and tranny E4OD. What a piece it is. Rebuilt it 4 times already in 300K miles. And I vary rarely haul much....afraid to blo0w the tranny again! I tried to find out once if there was another type of tranny I could put in the truck, but didn't have any luck without having to do some real radical mods!
Mike
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