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Old 05-12-2007, 07:02 PM   #1
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Overall I'm happy with the purchase of my DP. About the only thing I'm disappointed in is the torque that the C7 puts out when I'm hill climbing. Are there any mods that can be done that won't void my warranty?

Craig
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Old 05-12-2007, 07:02 PM   #2
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Overall I'm happy with the purchase of my DP. About the only thing I'm disappointed in is the torque that the C7 puts out when I'm hill climbing. Are there any mods that can be done that won't void my warranty?

Craig
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Old 05-12-2007, 07:10 PM   #3
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What sort of performance do you feel is lacking? Hill climbing? Fuel economy? Acceleration?

You can improve performance in various ways, but it is seldom a worthwhile goal to simple "add torque" (or horsepower either). Often it is beneficial to change gearing, improve air intake or exhaust, or change/reprogram the transmission to alter shift profiles, or perhaps even alter the engine management chip, but you should always have some specific performance improvement in mind when doing so and select the mod that will deliver that improvement.
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Old 05-12-2007, 07:13 PM   #4
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Hi Gary,

Acceleration and fuel economy are fine, it just seems to crawl when climbing grades. I'm still fairly new to this DP way of life, so maybe I'm expecting too much.
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Old 05-13-2007, 08:20 AM   #5
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It's not unusual to run out of acceleration on grades, even though the engine does not seem to be laboring. We are accustomed to be able to put our foot down and accelerate up a hill in a passenger car but that isn't going to happen with a 26,000-40,000 lb rig. I feel as though I would like a bit more myself (370 HP Cummins ISL - 1200 ft lb of torque), but when I look at the speedo I'm actually doing well enough and the rig is moving right along without apparent strain.

What is the total weight of your rig when loaded for travel (and toad attached)? What sort of speeds can you maintain on a long 6% grade? If it is in the 50+ mph range you are doing OK. The rule of thumb is that you need about 1 HP per 100 lbs for decent performance, but "decent" is a matter of personal opinion.
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Old 05-13-2007, 03:20 PM   #6
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We have been told to use our allison in the following way to improve hill climbing, down shift manually to one or to gears lower than you are in prior to reaching the incline, then just let her climb, the only downside (no pun intended) is that when you reach the top of the hill before heading down you have to manually put her back in 6th gear it won't do it automatically and if you want the automatic to take over for the decline along with your jake/engine brake you need to shift back to 6th.
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Old 05-13-2007, 03:52 PM   #7
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CMonroe,

Another tact is to let your Allison do the shifting when climbing a mountain. Make sure it is NOT in the economy mode, and let it find the gear it should be in. This way you don't have to worry about making sure the tranny is in the right gear when you get to the top of the mountain.

Watch your engine temp; if it begins to climb too high, downshift to keep the engine at 2000 RPM's which is an optimal cooling RPM.

This may not have you climb the mountain like your SUV (or mine!) but it may be the optimal way to climb the mountain.
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Old 05-13-2007, 07:46 PM   #8
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All are good advice Craig, but the part of your post that got side tracked is the most important. And that is that ANY power upgrade make to your stock engine will most likely void your warranty in the event of a major engine failure. All major manufactures are very sensitive to "improvements" that are made to their basic platform, unless it is one that they authorize themselves.

If the DP is new to you, give it a little time. I too thought I was moving too slow at first when I brought home the new rig. But after adjusting to the size, weight, and ability of my rig, I am quite satisfied with the performance. My recommendation is to drive it for six months to a year, and take some long trips of two weeks or better. Then if you still feel it is under powered, then you can start adding performance add ons. Just remember the formula for power in a diesel is air+fuel. And for the price of fuel these days, topping that hill 5 MPH faster may not be worth the money spent in fuel, or the modification.

Just my .02

Sarge
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