I have a 2004 F250 SD SuperCab w/6 foot bed, 5.4L engine and auto OD transmission. I normally get 13-15 mpg on the highway. While towing a 21', 5klb travel trailer, the mileage dropped to 8.8mpg. On Florida's fairly level highways, the truck wouldn't stay in OD. At 70 mph in OD the RPM is about 2k, when out of OD the RPM at 70 is about 3K. What modifications would help increase the engine torq around the 2000 rpm range? Would a small supercharger get the added torq at the low rpm? I would like to find a simple, less expensive way to get better low end torq. Any suggestions?
Thanks for your suggestions.

 

Been looking into the same thing myself. The best mod I've found so far (relatively cheap) is to change ring and pinion gears ie. 4.10 or 4.30. (going by your rpms you probably have the 3.73) I've read that it requires reflashing the EEC to help with tranny shift schedules. However, today I talked to service mgr at my local dealer and he said that would not be necessary. So who knows what the story is. For sure some software mod is needed at least for the speedo.

 

trade it in for a diesel? lol. you should be able to to get a chip for it. you can change the gears but your rpms will be higher at 70

 

Also, the service guy told me that it would not effect the warranty to have the gears changed by a "reputable" shop. I wonder if my single car garage can be considered a "reputable shop"

 

I've done a few things. Before the gears, I was down shifting going up hills without a load. I pulled a boat across gainesville a few months ago and never down shifted with the 4.56 gears and 35" tires. The ratio works out between 4.11 and 4.30 with a stockish sized tire.

I want to try a modified Y-pipe next.

 

If you have 3.73 gears and still run stock size tires a gear change to 4.30s will make a very noticable difference. The SPD Ypipe will incease low end a bit and help across the entire rpm range. An tuner with a good custom tow tune will help a lot also.

 

Well, as one with the almost same specs as you (my truck is a 2003 and a crew cab), I can tell you exactly what a gear change will do. I went from a 3.73 to a 4.30, and I also pull a travel trailer. Mine weighs in at roughly 5500 pounds loaded (26'). With the change from 3.73 to 4.30, there was only a slight difference in being able to maintain OD. I live in southeast TX, and have a lot of the same "relatively flat" land Florida has. The biggies are the overpasses and such. Again, the 4.30 made some difference, but not a lot. It did help a lot pulling my 4100 pound boat. The big difference...wind resistance. The TT has a lot more wind resistance.

Anyway, I really don't think you're ever going to be able to do enough to make a big enough difference without going to the diesel. Even with the 6.8L I've heard the same things about not being able to run in OD pulling any kind of a load. They just aren't made to do that, where the diesel is. It makes its peak torque in the lower RPM range, where the gassers make their peak torque in the higher RPM ranges.

Now, the 4.30 will give you better "git up and go". In other words, from a stop, you will be able to get to your cruising speed more comfortably. Your RPMs will increase about 200 to 300. And your gas mileage will decrease very little. I have been averaging almost 15.5 mpg in my daily driving (35 miles one way to work, 35 miles back home...average driving elsewhere). Pulling my trailer last time out I got about 9 mpg. The RPMs are about 2200 or so at 65mph, and up around 3100 when OD is disengaged. I have pulled my TT without OD for great lengths and still maintain that near 9 mpg.

So, I think what I'm trying to say is, if you want better low end torque, your only real answer is a diesel. I just don't think you will ever be able to make it work in a gasser. And the above is all real world...I drive my truck almost every day to work and back. Other than the 4.30 rear end, I have a K&N filter and I also have a Supertuner that helps with the shift points when pulling, but doesn't do a whole lot for added torque or gas mileage. Otherwise, it's all stock.

 

Short of an engine swap, custom tranny or buying a new truck, your choices are:

1. Chip/programmer to increase engine output
2. Taller gears in the back to increase RPMs (and decrease MPG)
3. Shorter tires to effectively increase rear gearing (same MPG effect as above)

 

if you are trying to drive 70 and stay in overdrive at 2k you dont need to increase your low end torque. trq gets you off the line, at 70 you are already moving. once moving horsepower takes over. so you need to up your horsepower. but as you increase one you normally increase both. things to do to help you out. headers and 3" dual exhaust maybe even throw in an h pipe. a true cold air intake will help. but with these mods your talking probably around 1000 maybe a little more. you would be better off going to the v10 or if mpg is important the diesel. if price is no big thing you can always keep moding your current truck by putting in a bigger cam and having your intake and heads ported and polished. you would see some big gains in power there. but your best bet is to just buy a better truck with a better engine

 

the insecure diesel owner strikes again, just help the guy!

 

So full of misinformation I don't even know where to start...

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Andi's-Bronco, a supercharger WOULD be a good option to increase the output of your engine and depending on the type, it will help in the range you're looking at. However, they're pricey and unless you own your truck out-right and you love it to death then the cost may not be worth it.

I would regear first. There's a reason why deeper geared trucks are rated to tow more.

Don't throw a lot of money for "bolt on" mods at it. A tuner with a CUSTOM tune would be of benefit. Mike at 5-Star tuning could hook you up easily. www.5startuning.com

You already have a true cold air intake and headers and such won't gain you much...except for noise.

 

the guy with no ***** strikes again. whatever helps you sleep at night. i bet you like to cuddle up with your papers that say a v10 has more hp and suck your thumb. its all good!

i was actually trying to help the guy but you had to push your commie ways in this thread to

 

You might want to look at 2005-2009 Gas 6.8L V-10 as it has more HP than a diesel.
You now have 260hp- 350 tq. The V-10's are 362hp-457tq.

 

Honestly the diesel is not going to get great mps towing. 5-10k loads in a stock trailer net me 11-13mpg. I do have the power and I can stay in overdrive as well. Unloaded in town is 14.5 for me and 17-19 on the hiway. So given that if you looking for mpgs yes they are better the power is better. As for the truck in question the biggest gains will be from tuning which will help across the board. Maybe not the gains a diesel will get but gains. The next thing will be gearing and putting the rpms at 65-70 a little higher to compensate for the 5.4 powerband. Modding the exaust, headders, cam, polishing heads etc will help but be a big cost with little gains. Remember when you do all that you will have to upgrade a lot more to see a true benifit at substantial cost. The supercharger idea is great but there are not that many options in that area unless you want to build it your self. If you like the truck spend about $1000 bucks gear it and tune it and you will most likely be supprised at the gains for the dollar. Also if you regear you will need to have the spedo corrected which ford can do.

 

The speedo will not have to be redone. Mine is spot on after the rear-end change. It was explained elsewhere, but suffice it to say, it will not need to be changed.