LACK OF TORQUE IN 4TH & 5TH \ TIRE SIZE, GEAR CHANGE? - Ford Powerstroke Diesel Forum
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post #1 of 18 Old 02-14-2011, 03:35 PM Thread Starter
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LACK OF TORQUE IN 4TH & 5TH \ TIRE SIZE, GEAR CHANGE?

I have a 2005 CC F250, 3.73, auto 4x4 and running 34" tires or 275/65R20 and the truck seems to pull really free and easy till around 40 mph or I'm guessing till 4th gear. I have put a tune on it and it is really quick and strong when getting into it but it just seems to be torque less under normal acceleration with or without a load. This is my first diesel truck and I was just expecting it to maintain speed when pulling a hill better than it does. I have a hill that I regularly go up that's probably 1\2 mi at 3-4% grade and running empty it really takes a lot of throttle and many times a down shift to maintain 55mph going up it. My friend had a 2002 7.3 with 3.73 and 35" tires and he drove mine the other day and said it felt totally different than his, claimed it was probably faster off the line but from a roll on at 50 mph he said the 7.3 he had would accelerate quicker and with no down shifts.


Been thinking of going to a 32-33" tire or if within reason changing to 4.10 gears, anyone feel the same about these trucks or played with the tire size and gears?
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post #2 of 18 Old 02-14-2011, 03:53 PM
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My truck had the same problem. I have a 1000' elevation change in 12 min to do every day on my commute. Some parts are very steep and it seemed like I had to go full throttle just to get up the dam thing doing 80km/h. SCT and custom tunes and now the truck doesn't even shift out of high gear on the steep stuff and I can hold 90 km/h no prob.
My sct x2 used was $100, and three tunes from matt, including SRL which is a great DD was annother $100. Glowshift EGT gauge $100

A heck of a lot cheaper than tires/gears, and way more fun

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post #3 of 18 Old 02-14-2011, 04:17 PM Thread Starter
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Quote:
Originally Posted by HawaiiBake View Post
My truck had the same problem. I have a 1000' elevation change in 12 min to do every day on my commute. Some parts are very steep and it seemed like I had to go full throttle just to get up the dam thing doing 80km/h. SCT and custom tunes and now the truck doesn't even shift out of high gear on the steep stuff and I can hold 90 km/h no prob.
My sct x2 used was $100, and three tunes from matt, including SRL which is a great DD was annother $100. Glowshift EGT gauge $100

A heck of a lot cheaper than tires/gears, and way more fun
I too am running a SCT with the SRL+ tune from Matt and it makes great power but it just feels like the truck doesn't have enough gear to me. If you drive it hard now it will go but I'm looking for it to run a little easier under normal acceleration. When driving easy it will accerlerate up to about 40 mph with little throttle but from there to get it to increase speed your really have to push down on the pedal.
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post #4 of 18 Old 02-14-2011, 04:31 PM
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You need to find out when the converter locks. Eric's x-street locks the converter after 40mph. And his x-race locks in at 2nd gear.

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post #5 of 18 Old 02-14-2011, 04:44 PM
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My understanding of why these trucks don't seem to perfor well ati higher speeds is the wind resistance becomes a real issue. At higher speeds you utilize the hp morethan the tq. Our trucks tuned dint have any more hp than a dodge hemi pushing a 2000lb lighter truck

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post #6 of 18 Old 02-14-2011, 04:45 PM Thread Starter
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Quote:
Originally Posted by Lilpooh View Post
You need to find out when the converter locks. Eric's x-street locks the converter after 40mph. And his x-race locks in at 2nd gear.
I guess when the converter locks up then you would have to give it more throttle to accelerate as the RPM's would drop off along with the torque, am I on the right train of thought?
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post #7 of 18 Old 02-14-2011, 05:04 PM Thread Starter
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I think ideally lowering the 4th and 5th gear ratios in the transmission would be great but I don't think that would be very cost effective

I was pulling a tractor on trailer combo weighing around 10K the other day and it gets that load moving fairly easy, with little throttle input, up to 35-40mph but after that I really had to give it the throttle to get an increase in speed form there, makes me worry a little about taking a trip to the mountains with a 6K load, I'll probably get about the same MPG as I did driving my friends Chevy 6.0L gasser, 7.6MPG
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post #8 of 18 Old 02-14-2011, 05:09 PM
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Some people(not me) increase the rpm limit so that when the truck shifts, there will not be as much power loss because the drop in rpms are not at the lower levels.
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post #9 of 18 Old 02-14-2011, 05:15 PM
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I am in the same boat 35" tires with 3:73 gears and its tuned and runs great up to about45/ 50 mph after that its all down hill. We need gears I am thinking around 4:88's to 5:13's just look at your RPM's when your cruising at 55 mph you should be at about 2100 RPM's but I am sure you are at about 1600 to 1800 RPM's
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post #10 of 18 Old 02-14-2011, 05:20 PM Thread Starter
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Quote:
Originally Posted by smokersteve View Post
Some people(not me) increase the rpm limit so that when the truck shifts, there will not be as much power loss because the drop in rpms are not at the lower levels.
I just sent Gearhead an e-mail and maybe there can be a little tuning to improve this but I think there could be a better gearing setup to make these trucks run a little freeier without having to throw more fuel to it, talking normal acceleration here, sometime more fuel is fun but that's reducing with this $3.55\gal fuel
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