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Old 04-29-2018, 05:32 AM   #1 (permalink)
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Input for Ecomodding A 2.8 Duramax Van

Recently purchased a Chevy 2500 Full Size van with the 2.8 Duramax, 8 speed Allison auto trans. Fuel mileage is really impressive. I have about 5000 miles on it, running about 7500 lbs to 8000 lbs GVW. With a full tank of driving in city of Chicago traffic (no burbs) we are getting about 21 mpg. Just took it out on a short highway trip and it's getting about 27 mpg at 65 mph and about 31 at 70 mph. At about 67 mph it upshifts and rpms drop from 2100 to 1500.

I've also noticed it appears the trans is programmed specifically for heavy loads.... it holds low gears for a long time before upshifting.

I don't know much about diesels, so any input would be helpful. I suspect engine loads are closely monitored by the electronics, so if I do some aero modding (probably a front undertray and reduce amount of wasted air going through the grill and not the radiator), it may upshift at lower speeds on the highway and be able to hold high gear at lower rpms. I imagine if I can hold high gear at 60 to 65, I could be running about 1400 rpm on the highway and pulling down mid to upper 30's MPG's

Is there any place that has the factory CD for these vans. It's nice to know where I'm starting.

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Old 04-29-2018, 11:45 AM   #2 (permalink)
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Originally Posted by 93tracerwagon View Post
Is there any place that has the factory CD for these vans. It's nice to know where I'm starting.
The cD has to be huge on that vehicle with that brick rear end...I googled it and got 0.52 (source here).

Have you tried coasting down hills in neutral? With that weight you should have some impressive coasting ability, regardless of how bad your cD is.
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Old 04-29-2018, 01:05 PM   #3 (permalink)
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Well if you weren't in the peoples republic Illinois in ome of the smoggiest areas in the country I would say gut the emissions system and run an emissions gear free economy tune.

Make sure it's got cold air intake for summer and try a warm air intake for the winter.
Make sure the air filter stays clean.

Aero mods are a good idea since the van was likely designed for at least some mild off roading that would remove most aero mods hung down low.
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Old 04-30-2018, 01:31 AM   #4 (permalink)
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I'm surprised I haven't heard more about this option on the GM full size vans. It just sort of sits out there unknown. If you can average good MPGs then you really have something. I can get almost 30 MPG out of my Grand Caravan at 65 mph steady but normally about 18-19 although mostly city. If a 2500 12 passenger can also do that, that's amazing.
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Old 04-30-2018, 10:05 AM   #5 (permalink)
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The 2.8 Duramax is a new option

2017 was the first year. The Colorados got it in 2015 and its had some great reviews from them too. The Colorados only have a 6 speed auto, however, and it is a more expensive option because its part of a package.
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Old 04-30-2018, 10:42 AM   #6 (permalink)
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Its a good deal more power from this diesel than with gasser straight sixes of yore.

As to modding, basics first:

1). Garaged. Full enclosure.

2). Use of block heater year-round.

3). Every trip planned in advance. “Warm-up” is about travelling to farthest point first (as possible). Choose steady-state longer routes over shorter stop & go routes. IOW, instead going across-town, I’d head away from town to an outer freeway loop and use it. Metro highway average mph is 35. Surface streets is 15-mph.

Planning also means EVERY stop. Not just fuel. No random choices to whip into convenience stores. Part of planning is supplies. An ARB or Engels or Dometic “off-road” refrigerator. Your helper “forgot” food/drink? Tough. You pay him, you don’t sudsidise behavior that costs you time & money. Vehicle wear.

Planning is also investigating ingress & egress. A sat map photo beforehand. Fewest number of steering wheel turns to arrive and depart. (It’s not just parking). As to parking, backing in only. Don’t care how many times you’ve been there start fresh.

Use MalQuest to see Best Order Routing. (No left turns, period).

4). Eliminate idling. Not ever necessary. Kills mpg rapidly (pretty well nothing worse).

5). Posture and mirrors. One never has to reach or lean if it’s correct. Same for exterior glass treated with RainX or Aquapel. Mirrors and side glass matter, windshield not so much.

6). Use Blue Beacon at least monthly for washes. Other, for weekly maintenance.

7). Be adamant about vehicle TIME and miles service intervals. Have appointments set in advance. Unbreakable.

8). As to stunts like being out of gear downhill, don’t. Ever.

9). Tires, shock absorbers and anti-roll bar bushings can all be upgraded. See what the local ambulance companies are running for tires and inquire (Michelin should be first choice). Bilstein shocks if available. Polyurethane bushings. Now, not some day.

10). Record all miles and all gallons. Your “mark” is Average Miles Per Hour, so you’ll also want to be able to read Engine Hours. If you can keep average MPH above 27 you’re doing well for metro work. MPG will fall into place by routing, timing (never stopping) and shutting off engine when parked (never idling). No exceptions.

Again, it’s MPH Average, not MPG that should concern the FE conscious truck driver. The latter follows the former.

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Old 04-30-2018, 11:59 AM   #7 (permalink)
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Have you already tried to contact Black Bear Performance? They might be able to provide a different tuning to the electronic controls of your transmission in order to enable some earlier shifting.
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Old 05-01-2018, 11:09 AM   #8 (permalink)
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Thanks for the input

I noticed Calibrated Power is just north of Chicago...any experiences with them? Also, I do have a concern regarding factory warranty if changing tunes.
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Old 01-15-2019, 05:57 PM   #9 (permalink)
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Congrats on the great mpg. I've wondered about the baby diesel. Great to hear.

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