tech help possible gear mod
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Freshman User
Joined: Apr 2010
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From: texas
tech help possible gear mod
94 f-350 xlt crewcab dually, powerstroke 7.3 turbo diesel w/ direct inject. Gets 10 mpg, want 20 mpg suggestions wanted on gear reduction in rear end, or tranny swap with lighter trans if possible. or combination of both
This truck i cannot bring myself to sell, i wish to use it as my daily driver and do not need the high gears for towing or hauling. i wonder if this is even possible to do. first thought was propane inject, or comp, chip. and rpms are 50-1800, 55-2000, 60- 2200, 65-2450, 70-26000 rpm, seems this is alot of the problem in my mind.
any suggestions are welcome, i have just sunk $1100 into brake drums/ rotors, front end alignment etc. looking to increase my mpg, then the bling will be next.
This truck i cannot bring myself to sell, i wish to use it as my daily driver and do not need the high gears for towing or hauling. i wonder if this is even possible to do. first thought was propane inject, or comp, chip. and rpms are 50-1800, 55-2000, 60- 2200, 65-2450, 70-26000 rpm, seems this is alot of the problem in my mind.
any suggestions are welcome, i have just sunk $1100 into brake drums/ rotors, front end alignment etc. looking to increase my mpg, then the bling will be next.
Postmaster
Joined: Jun 2009
Posts: 2,566
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From: Monroe/Ellensburg, WA
Welcome to FTE! First off, keep in mind that you have a crewcab dually and getting 20 mpg is askin alot. With that said, i would say you have 4.10 gearing, only other option was 3.55 i believe but im not sure how that would work with having a dually. Obviously a dually was made for towing and thats why you have 4.10s. Usually at 75 with 4.10's rpms are at 2500. You have a manual right? I think that was the only trans for a 94.5 powerstroke. A chip will help you out a bit for fuel economy so if it were me, i would start there.
Posting Guru
Joined: Nov 2007
Posts: 2,158
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From: West Texas
I have a crew cab 4x4. Same difference for gas mileage. I get 20-22 though on the highway empty. I get 14-16 with this camper on it. As long as I'm not driving into a head wind.
Your truck is sick. Mines running as right as it can run with the stock 94 computer in it. All I've done is a tymar 3-4 inch downpipe and 4 inch exhaust and I did a 6637 air filter mod.
Seriously, something is wrong with your truck if that's all it gets.
Some big things that effect mileage on mine is tire air pressure. the door sticker says 60 and 80. I run 70 and 80. I used to go down to 50 front and rear for comfort and gas mileage went right down with it.
I also have oversized tires. 265's. It kinda screws up my sweet spot for towing because they reduce my engine rpm some and they also reduced mileage a bit when I'm loaded down. Empty, no difference that I can see.
Is your clutch slipping?
How about the pcm? Is there a chip on it? The older ones just killed mileage. I found one on mine when I got it and taking it off all kinds of things got better.
Before you go trying to mod it for mileage just make sure everything is right on it first. Otherwise you will be chasing your tail for years trying to figure it out.
Your truck is sick. Mines running as right as it can run with the stock 94 computer in it. All I've done is a tymar 3-4 inch downpipe and 4 inch exhaust and I did a 6637 air filter mod.
Seriously, something is wrong with your truck if that's all it gets.
Some big things that effect mileage on mine is tire air pressure. the door sticker says 60 and 80. I run 70 and 80. I used to go down to 50 front and rear for comfort and gas mileage went right down with it.
I also have oversized tires. 265's. It kinda screws up my sweet spot for towing because they reduce my engine rpm some and they also reduced mileage a bit when I'm loaded down. Empty, no difference that I can see.
Is your clutch slipping?
How about the pcm? Is there a chip on it? The older ones just killed mileage. I found one on mine when I got it and taking it off all kinds of things got better.
Before you go trying to mod it for mileage just make sure everything is right on it first. Otherwise you will be chasing your tail for years trying to figure it out.
Posting Guru
Joined: Nov 2007
Posts: 2,158
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From: West Texas
With a 3:55 and a stock 94 you will absolutely hate towing anything. Trust me. Mine is 4:10 like yours and at 65, which is as fast as I really care to go with that top heavy camper on it, I am running 2300 rpm. It's barely able to make 10 psi boost at that speed. At 70-75 I can get it up to 20 and pass just about anything. Even when I also have the horse trailer behind it. Like I said, I'm out of the sweet spot for power. If you go higher on the gears then you will either need to go faster or run in 4th to pull heavy. Then watch your mileage go to crap.
FWIW, like it s in this picture I am about 10,500 pounds. That's empty of water and passengers. Everything full and horse trailer on and loaded I am running 29,000 pounds. I can barely do any hills in 5th like that but it's ok in the flat areas. Just imagine if it had 3:55 gears though.
I really think something is wrong with your truck.
FWIW, like it s in this picture I am about 10,500 pounds. That's empty of water and passengers. Everything full and horse trailer on and loaded I am running 29,000 pounds. I can barely do any hills in 5th like that but it's ok in the flat areas. Just imagine if it had 3:55 gears though.
I really think something is wrong with your truck.
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Freshman User
Joined: Apr 2010
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From: texas
i agree something could be amiss, i am wondering if our trans are the same, my business partner had same truck without dually and his trucks rpm ran at 70 what mine ran at 60. which led me to believe its the tranny or gears in the dually. all things equal then yes my baby is sick. i never noticed the difference when hauling with the dually. seems the more you put on her the smoother she ran. these days all im towing is my camper to the beach. note, i never use first gear, start out in second ,
Posting Guru
Joined: Dec 2005
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I have a 4x4 f-250hd converted to a dually with 3.55 gears. Keep in mind, we have 1/3 more rotating mass on our drive train, 1/3 more rolling resistance, and those dually flares act like sails and disrupts air flow really bad.
With that said, I think your truck is sick as well, I've pulled 20,000+lbs with my truck with 3.55 gears holding at about 60mph, I dropped out of overdrive and the engine just wistles down the highway through the rolling hills. milage i would say is floating around 13 mpg but I got a lil more rpm on you doing 60 mph with no OD compared to 4.11's with overdrive.
My best milage was 21mpg but i was keeping the speed at 58 mph on the highway and that was 95% highway driving(empty). my milage is atainable but painfull to do with the dually.
Poor milage can be clogged CAT, plugged filter, worn injectors and the exhaust tube on the right side manifold on the front that supplies back pressure to the exhaust back pressure sensor can plug or rust through which effects milage big time from what I understand. Thats just a few things off the top of my head.
With that said, I think your truck is sick as well, I've pulled 20,000+lbs with my truck with 3.55 gears holding at about 60mph, I dropped out of overdrive and the engine just wistles down the highway through the rolling hills. milage i would say is floating around 13 mpg but I got a lil more rpm on you doing 60 mph with no OD compared to 4.11's with overdrive.
My best milage was 21mpg but i was keeping the speed at 58 mph on the highway and that was 95% highway driving(empty). my milage is atainable but painfull to do with the dually.
Poor milage can be clogged CAT, plugged filter, worn injectors and the exhaust tube on the right side manifold on the front that supplies back pressure to the exhaust back pressure sensor can plug or rust through which effects milage big time from what I understand. Thats just a few things off the top of my head.
Posting Guru
Joined: Dec 2005
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i agree something could be amiss, i am wondering if our trans are the same, my business partner had same truck without dually and his trucks rpm ran at 70 what mine ran at 60. which led me to believe its the tranny or gears in the dually. all things equal then yes my baby is sick. i never noticed the difference when hauling with the dually. seems the more you put on her the smoother she ran. these days all im towing is my camper to the beach. note, i never use first gear, start out in second ,
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Posting Guru
Joined: Nov 2007
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From: West Texas
Mines the same gears and the transmission is the same too. It's a zf42 in the 94 model. That's all they came with. I'm abut to upgrade my trans to the zf 47. It's a direct swap with a bit more useable gears in it. Much more heavy duty too.
The dually 2 wheel drive and 4x4 f350 SRW really are equal mileage wise. Mines taller than yours adding a lot of wind resistance and the dana 60 up front makes up for the weight. Seriously there is no reason any of the obs trucks can't get 20 mpg.
The dually 2 wheel drive and 4x4 f350 SRW really are equal mileage wise. Mines taller than yours adding a lot of wind resistance and the dana 60 up front makes up for the weight. Seriously there is no reason any of the obs trucks can't get 20 mpg.
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Thread Starter
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Freshman User
Joined: Apr 2010
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From: texas
[quote=RRranch;8774762]Mines the same gears and the transmission is the same too. It's a zf42 in the 94 model. That's all they came with. I'm abut to upgrade my trans to the zf 47. It's a direct swap with a bit more useable gears in it. Much more heavy duty too.
i believe our trucks are the same, i didnt know the trans and rear were the same. seems as if you may have the answers i need. i would be interested into any information sites or aftermarket sites you knowabout pertaining to our trucks .
i believe our trucks are the same, i didnt know the trans and rear were the same. seems as if you may have the answers i need. i would be interested into any information sites or aftermarket sites you knowabout pertaining to our trucks .
Thread Starter
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Freshman User
Joined: Apr 2010
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From: texas
i am new to this site , and am very appreciative of the information i will learn. this is too cool to have someone with the same vehicles to converse with. i am looking to put quite abit of money into this vehicle over the next few years. the information i will gain i can already see will definately be benificial.