Taming the Beast - Making a GMC 2500HD... Less Terrible

[az_eric]

Old thread i know, but any updates? I own a 2007 2500hd classic cclb 4x4 and having hard time breaking 11mpg. Currently have headers, exhaust, volant intake, black bear tune, and e fans. I honestly haven't seen even 1 mpg increase with any of this.

[mpg_numbers_guy]

Originally Posted by az_eric

Old thread i know, but any updates? I own a 2007 2500hd classic cclb 4x4 and having hard time breaking 11mpg. Currently have headers, exhaust, volant intake, black bear tune, and e fans. I honestly haven't seen even 1 mpg increase with any of this.

My family has a 99 2500hd, same body style as yours, and it is definitely a gas hog, 12-13 mpg driving, 8-9 mpg towing. With something that inefficiently designed, small things like that won't make much of a difference until the low hanging fruit is taken care of: smaller engine, much taller geared transmission, skinnier taller tires, aerocap in the rear, and an airdam would be necessary to see any major FE gains. Other than that the #1 way to improve FE would be driving style, mazimizing coasting time in neutral or with DFCO. EOC if it was a manual.

[az_eric]

Yeah my driving style i know hurts. I drive a company van all day at work and sometimes i just want to get on it and hear the exhaust lol. And honesty i only drive it like 5k miles a year. I need new tires coming up and am going to switch away from the all terrains to some highway treads. I would love to switch over to a 6 speed manual transmission but the cost is too much for a truck that barely gets driven right now. The one think i really want to do is convert to manual locking hubs. I could see real improvement there, but again the cost is high for the rewards.

[Deezler]

EcoModder! Wow, blast from the past. Glad it emailed me about this thread.
Having two young kiddos makes it harder to find time to care about aeromodding and hypermiling, lol. Sorry all my photobucket pics are dead. F U, photobucket. Not redoing those. Imgur for the win.

Not too many updates from me on my 03' ext-cab short bed 2500HD. I did get new wheels and tires. The Michelin LTX M/S are amazing tires, great grip wet, dry or cold. But I did go bigger and heavier... not an mpg gain, oops. Can still get solid 14-15mpg tanks in mixed driving.



My truck is up to 107k miles now. I really don't drive it very much. Went through two cheaper VW GTIs as daily drivers, both needed a bit of work and then I flipped them for modest profits after about a year each. Got used to about 30mpg in each of them, though they both required premium gas.

And then I just recently impulsively jumped on a new VW Alltrack when I realized they weren't making or selling them anymore after the 2019 models - last chance to get a turbo, 6-spd manual-trans, AWD family wagon. Only $22k NEW, with a 6-yr, 72k mi warranty. Currently getting a steady ~30 mpg in mixed driving, might be about all she can do.

Hadn't really thought about any more aeromods for my 2500HD. With only local driving to tow and haul stuff, and ~2000 miles of driving per year now, it just doesn't make sense to prioritize spending time on. BUT! We just got a new camper to haul around, which means highway trips to camping destinations. So a couple items are back on the table that I sadly never got around to - lower air dam, front wheel spats, maybe some undertray action. Will any of that matter when pulling a huge, dirty brick behind me at ~9mpg? Dunno, but seems more worth trying now.

[Deezler]

Originally Posted by az_eric

Yeah my driving style i know hurts. I drive a company van all day at work and sometimes i just want to get on it and hear the exhaust lol. And honesty i only drive it like 5k miles a year. I need new tires coming up and am going to switch away from the all terrains to some highway treads.

Driving style is the easy one, man! coast, coast, coast.

DFCO is tough in these trucks, mine has to be above 60mph when starting a coast down or it wont even bother. My scan gauge has taught me that when cruising a back road at 55mph, it is actually beneficial to accelerate gently to ~62 first before a coming turn or stop sign, to coast down on DFCO as much as possible.

Tires are huge too. When I got my 20" wheels, I really wanted some K02 all terrains for style and off-road capability. But you know what? Michelin LTX M/S tires are just as capable with fresh tread, and then you get completely QUIET driving and definitively better mpg. My 265/60/20 LTXs were only $215/tire, too. Highly recommend.

I'm surprised your electric fans didn't help more. That job is still on my list, contemplating doing it at the same time as a cam-swap. An LT1 or LS2 cam would really wake up the 6.0L LQ4, and presumably not hurt mpg - need to further verify that part though.

[az_eric]

I have a very heavy tool box ladder rack deal on my truck. I removed it to help a friend move some furniture and kept it off until after a 400 mile trip to my dads iver Christmas. Tried to keep it about 5 over the speed limit to keep me in the left lane and avoid constant lane changes as its mostly 2 lanes each direction. Went from 9-10 mpg to 12.8mpg on the way there and 12.5 on the way back.
Im now using it for work again so the box/rack is back on and again getting about 9.5-10 average. The traffic out here doesnt help me at all though. We'll be going 65-70 and then come to a stop on the freeway and immediately back to 65.
Being said im looking into getting a 2.8l duramax van this year. Ive read good reports 20-35 mpg depending on load and driving. If i go that route truck will go back to big load and towing only duty.

[oil pan 4]

The best roof racks are easy to remove so you only put them up when needed and take them off when not needed.

[Deezler]

Well it's too bad that photobucket stole all my pics from this thread (and many others).

But I still have the 2500HD. Probably never getting rid of this beast, it's just too good and new truck prices are astronomical, of course.

I did complete a couple more aeromods last summer, in advance of a 2000 mile camper road trip.

Most importantly, a front air dam, finally. The 4" tall lawn edging looked big in my hands, but on the truck, it's clear that 6" tall would have been better. Oh well. Combined with some front wheel spats that my front tires rub on. And one extra piece of coroplast behind the air dam to smooth any flow that sneaks under it.



Then a bulb went out in my center cab-clearance light atop the roof, and I decided to finally try fabricating a more low-profile setup with LEDs. Was not easy, but I think it works.





Unfortunately the truck had to sit outdoors all winter long. So she got some detailing love this past weekend. I don't intend to daily drive it again, but we have a lot of projects on the ranch for this summer/fall and I'll be making a lot of errand runs for materials (lumber $ = ouch).



As for mpg these days. This is about as good as long trips or full tanks get. Significantly better than 12mpg, though.

[Vman455]

Originally Posted by Deezler

they didn't do much with aerodynamics yet for this generation...

This is just straight up wrong. I don't know where this idea that OEMs don't do aerodynamic development on trucks/SUVs/vehicles that the public perceives to be "unaerodynamic" comes from, but it isn't true.

I have several papers on the aerodynamic development of various pickup trucks, and while this generation GMC/Chevrolet trucks isn't among them, the development of the 1988 C/K is. The paper is quite long and detailed; it overviews not just the optimization of the 1988 model but has quite a bit of information on the development of the two previous generations of full-size Chevrolet trucks.

[Deezler]

Oh please. I was referring to the 2500/3500 trucks specifically, but still. I didn't say "none", either.

No front air dam. No underbody panels whatsoever. No wheel spats. No front grill smoothing or closures. No vents to/from wheel wells. No rear wheel well liners. No cares about bulky protrusions like antennas, roof cab lights, door handles, etc. No curvature at rear of cab or bed for slimming the rear wake, etc. Front track is 3" wider than rear. I could go on; there's dozens of areas where some basic engineering effort could have been applied, but clearly wasn't. This stuff was well known in the mid/late 90s when development of this platform was underway.

Bottom line, there was no return on investment for applying this kind of effort. I don't really blame them. Gas was $1.50/gallon, no EPA ratings for HD trucks anyway, and no one cared.