4.1 vs 3.73

eluther3 · Sep 12, 2016

Been towing my boat with my 98 expy 5.4L with the towing package. According to the stats, I should easily be able to tow this boat, with about 1500-2000 lbs of capacity to spare, but the truck labors and barely gets above 50 mph. My friend tows a larger boat with his Navigator with basically the same engine.

The previous owner put on larger tires (265/70 r16), so I think that may be affecting the performance. I'm considering swapping to a 4.1 ratio in the rear end to make up for the larger tires.

Has anyone out there done it? If so, how did it work? Cost?

Bedrck47 · Sep 13, 2016

First you need to provide more information.
Is your expy 2WD or 4WD
What axel ratio is your expy
You say the previous owner put on larger tires The 98 expy either had 16 or 17 inch tires.
What is the weight of the boat and trailer you are towing.

And even though your friend tows a larger boat than you with basically the same engine that is no comparison to what you can do with your expy He may have a different axel ratio that yours his Nav may be in better condition that your expy. (Engine and trans)

Bedrck47 · Sep 13, 2016

Stock tires for the 98 were either 16 or 17 inch

Front tires 255/70SR16.0 Front tires 265/70SR17.
Rear tires 255/70SR16.0 Rear tires 265/70SR17.0
Read more at https://www.cars.com/research/ford-expedition-1998/#hSWvyp7yUKofA61i.99

eluther3 · Sep 13, 2016

Expedition is 2wd. According to the VIN number decoder, my truck originally came equipped with 255/70 r 16 tires so 265s are larger tires. Also shows towing package with 3.73 gear ratio. I suspect his ratio is different, which is why I am considering this

MISTERgadget · Sep 14, 2016

The difference between those tire sizes is negligible. The non-pi 5.4 is a dog, no way around that.

Weigh the truck, weigh the trailer, figure out exactly what were dealing with here. Any weight in cargo, passengers, aftermarket parts, etc.. Will reduce your tow rating. Are the weights you're using for the boat considering fuel/water/coolers etc?

Tow ratings are also much more about weight handling and braking than performance. A tow rating doesn't guarantee a certain level or performance or acceleration.

Your friends navigator is likely a DOHC 5.4 that makes nearly 100hp more.

eluther3 · Sep 14, 2016

according to the VIN decoder and the trailer life website, tow weight for my truck is 8000 lbs. Boat is about 4500 lbs according to manufacturer. I have an aluminum trailer so even if you add another 2,000 for trailer, gear and fuel thats a total weight of 6500 lbs.

Ristin · Sep 25, 2016

I wonder if you're not having other issues. I have a 2000 Expy EB with tow pkg, 4x4 and 3.55 axle ratios on 265/70R17 tires. I tow a 27.5' travel trailer weighing around 6500lbs and have no difficulty getting to 55mph and above. Even on really steep grades (that fleet big-rigs climb at 8mph on the shoulder), I can maintain 45 and even a bit more if I really push it. This is with 2 adults, 2 kids, 2 dogs and all the crap that comes with them.
Prior to the Expy, I used Ford 3/4 and 1 ton diesel pickups as tow vehicles. I was concerned the Expy would not be up to the task but have been pleasantly surprised at how well the Expy tows.

1955moose · Sep 25, 2016

I agree with Ristin, you may have one or more catalytic convertors clogged, strangling your engine. Also something as simple as a fuel/ air filter swap can't hurt. One size up on tire size with affect torque some, but not like large wheel/ tire jumps. You might want to tune up if you haven't already, and have Exaust checked. One last thing make sure fuel pressure is up to *****.

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AZ59apacheguy · Sep 28, 2016

MISTERgadget said:
The non-pi 5.4 is a dog, no way around that.

Not trying to derale, but what is a non-pi 5.4L engine?

1955moose · Sep 28, 2016

Pi refers to the cylinder head type. The pi heads breathe better. Theirs a description on line.

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4.1 vs 3.73

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