Yet another pickup aero thread...with a twist!!
 

Currently running a 1996 C2500, with the 6.5 diesel. I use this truck for both escorting (pilot car for oversize loads), and OTR driving pulling contract freight, mainly travel trailers. This means that I put an incredible amount of mileage on my truck, I've been averaging LOF every 8 days. (5-7k miles).

The most important things for me are clean looks, increased mpg loaded or empty, and increased stability in cross winds.

I've been doing a fair amount of research, and have come up with some good ideas over the past few months. I am looking for some experience, and some opinions, as to which direction I need to go in.

Option 1: Full belly pan (near as I can). Issues would be melting it on the exhaust, allowing for rear axle flex, and dealing with the massive amount of heat that builds from that big diesel up front.

Option 2: Side skirts. No real issues that I can see here, with the exception of looks, and access clearance to the bottom of the truck.

Option 3: Deflector/spoiler for the rear. Issue here would be removing it to allow for gains while running dead-head miles.

Option 4: Duck tail off the back of the cab? Not real sure about that, though.

Whichever way I go with, a few key points need to be considered: The mods need to be effective while loaded with a travel trailer, or empty. (or in the case of the spoiler, removable/collapsible). I need easy (and frequent) access to the bed, for my tools and aux. fuel tank. Easy access to key components under the truck would be very nice, as I said, I run a lot of miles, and maintenance is a weekly adventure. And most importantly, it needs to be a clean, factory-looking install, so I don't draw attention from DOT.


Shoot me ideas! I've got some mechanical upgrades coming to help, but I've got to be able to do better than 11.2 loaded (with travel trailer) and 19.5 (empty, with cruise set at 62-64)

I think you greatly overestimate the heat from your engine. I bellied my Dodge and ran with NO FAN for over a year, only using the electric when towing the 5th wheel in stop and go or in the mountains. On the highway the fans can be left off.
http://ecomodder.com/forum/showthrea...sel-21857.html
I'd do the belly for sure.
Do you tow 5th wheels?
If not, we could design a very very cool adjustable aeroshell/canopy/travel trailer deflector setup. Time consuming and not cheap, but huge returns.
Think of a transformer back end.
When you deadhead, it would drop down to the best aeroshell you could do. When you tow a TT, it would come up square and have a deflector panel at the back 50% to get things started up.
The whole thing lifts up for total access, plus add a big side door or doors for filling that tank and getting to tools. Bonus is dry place and tools.

The 6.5 was never designed to be a powerhouse motor, or to be worked hard like a Cummins will. I have struggled to keep coolant temperatures under control in warmer weather, especially when running in mountains. Because of this reason, I think that I will be replacing the truck with something newer in the next few months, and keeping it around for daily driving use.

e-fans are on the list of things to do. I was planning on a dual speed fan from Lincoln Mark VIII with the 3.8L, it has worked flawlessly on my jeeps for years. Of course, new fuel injectors and glowplugs are on that list too.....It all takes money that I don't have at the moment.

Right now, the plan is to start with a factory airdam, added to the bottom of the factory airdam I already have. That should drop it down about 4-5 more inches.

I have two of those fans. So far I have only run them manually in low. I have the wiring about 80% for fully automatic 4 mode functions. I'll turn one on when stuck in city traffic solo, or both when towing through town.

Ok, another question. I have a raised bed cap, I'm wondering if this would be beneficial for use with the trailers? It should help kick airflow up over the top of the trailer, but I wonder if it will hurt my empty MPG at all?

Photos to be attached....
http://i164.photobucket.com/albums/u...3_111523-1.jpg
http://i164.photobucket.com/albums/u...905_134244.jpg

Another thought.....what about the use of a rear air deflector to break up the drag formed behind the truck? Similar to the ones found on older Blazers?
http://i164.photobucket.com/albums/u.../8952489_3.jpg

You want to click on the links in my signature below for ideas.

I went for down-force over mpg gains, and I'm happy with my choices.

This picture was getting a little dusty anyways...
http://ecomodder.com/forum/member-ae...mendations.jpg

Half you aerodynamic drag is in the underbody and wheelwells.

So... Full belly pan and wheels spats, at least 2 wheel skirts and attention paid to the inner aspect of the wheel wells. I suggest hangar door seal installed horizontally so it is brushed aside (down in front, up in back) when the wheels are turned.

For the rear difusser, I like this (more road clearance, obviously):

http://ecomodder.com/forum/member-fr...bonnevette.jpg

All the turbulent air in the rear wheelwell is pushed outward, where it is sheared off by the overall air flow. A full wheel spat [and skirt] would enclose the outer face, but I don't think it would add much and be in the way more.

That style of rear air deflector was installed to deflect clean air down across the rear window to try to keep it from becoming covered with dust and road grime being kicked up into the recirculating eddy trailing behind the truck. It wasn't installed to reduce drag.

Bajoos

I understand the original intent on that blazer spoiler, had installed one on my old Cherokee for that reason, back in the day. I was curious if the angle could be modified, to work either on the tailgate or the back of the cab

I've gotten quite a bit of good reading off those links, and really like some of your ideas. Thinking of trying to steal your rear spoiler idea, just extended higher to help with air deflection over the top of the TT

Looking at your posts and pictures I assume you never pull fifth-wheel trailers. they'd probably be too much for a 6.5 SRW.

I do have some thoughts.

Forget trying to do much while you are pulling a trailer. They vary a good bit and they dominate your aerodynamics. that's revenue mileage so don't mess with it. But if you're like most guys in your business, you never get backhauls so you really need to cut costs on the return trip.

I'd recommend you make a good aero-lid. It will, by itself improve your empty MPG by 2-4 MPG depending on how fast you drive. I had a very crude aero-lid and it garnered me 3 MPG improvement over an empty bed. there are a number of aero-lids guys on here have built. BamZipPow is working on something that looks a lot like what you want. You definitely need an opening hatch. Lack of hatch is why I got rid of my crude aero-top. Check out the "commercially produced aero lid" listed above. For aero excellence it is the gold standard. Bondo has off-the-charts craftsmanship few of us can begin to approach. Search and read all of Phil Knox' stuff. He has turned over every stone at least twice.

Something to think about: Some sort of replacement for your side mirrors. even your little ones (you ought to see the barn doors on my Ford) comprise at least a quarter of your aero drag. If you built an aerocap like BamZipPow, you could incorporate rear view cameras fair to the air flow. They'd be useless while towing a trailer but running empty or escort, you could fold the mirrors in and rely on the cameras to see behind you.

I used to own a 6.2 diesel. Run, don't walk away from grille blocks. Unless your cooling system is substantially better than mine was your cooling is marginal. It would take a lot of fuel to pay for a cooked engine. Cooling failure is why i still don't have that excellent old truck.

As you said you may want a newer truck (you may get into fifth wheels, too). But if you kept the old truck (I always like those years' Chevys) swapping in a Cummins 4BT and a stick shift would make you hard to beat for MPG. The little Cummins is essential two-thirds of a 12 valve and can be turned up to maybe 175 HP and still be bulletproof. The stick (NV4500 or ZF-6) would buy you an additional 2 MPG. that's a bit of a project but there are scads of guys in your neck of the woods that have done similar conversions.

Instead of a belly pan, how about an air dam for the front to deflect air from hitting the underside of the truck. It may not be as good as a belly pan, but it seems much more simple with the belly pan concerns you've stated.