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Old 08-30-2012, 05:05 AM   #1 (permalink)
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Replacing Class c motorhome body for touring act

First off, I love this forum. It's amazing what you guys accomplish with minimal materials and raw brainpower!

I'm new, but have been reading as much as I can take in. Forgive me if I'm not quite studied in all this aerodynamic fun.

I tour the country with a rock band of robots I made, and have been using this 19ft class c for the last 8 years. Due to VERY annoying local laws, I'm forced to put it in my short 16.9 ft driveway, and since the body is falling apart anyways, I figure now would be a great time to make this brick less of a brick.
Last tour I spent $8000 on gas, so if I can get even a 10-20% improvement, that's quite a bit. I don't figure its going to cost me too much, as I'm quite the scrapper. I find free/cheap materials often in bulk.

I know this 1972 class c isn't a great platform to start with, but if the Cd is really that bad it shouldn't be too hard to get a lot better with a totally new body, right?
I do have a gear vendors installed though. I love that lil guy....

In order to fit the robots most efficiently in the camper, I have to have it approx 8 ft wide. If I load lengthwise in a more narrow van, I have no room to live while on the road.

The plan so far is to remove the entire rv body, leaving the van front. I'll redo the very warped subfloor and beef up the side frame supports. Then make the roof slope up from the van front following the windshield angle, and then do a slight taper over the entire length of the roof to the rear.

I plan on feathering the body wider from the front doors rather than the flat wall extensions it has now. What were they thinking?

Overall, the plans include a lot of great stuff I've found here so far:
Side skirts, wheel fairings front and back, air dam, and Im going to make a hinged foldable tail to be out when freeway driving, but when parking I can fold and latch it out of the way to fit in smaller spaces (very important as many parking spaces I can just squeeze into now.

My questions will be many but I've got a few to start.
To keep it as light as possible, should I use metal studs for the framing, or should I use 2x4? I weld as well, so I could do square tubing, or whatever.
My plan was to skin it with galvanized sheet metal, and on the top edges having at least a 2in radius. I've seen the ideal aerodynamic template, and I'll try to adhere to the concepts, though the main ones being a constant taper inward slightly??? I'm going to Photoshop some body ideas to run them by you before I start chopping as I'm gathering materials.

I'll get a pict up soon....

Btw, does anyone know of a more aerodynamic roof vent? They really help cool off my camper in hot weather.

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Old 08-30-2012, 02:00 PM   #2 (permalink)
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I'd start with weighing the stripped chassis front and rear axles, and calculating where your load should be for weight distribution. Put the load as far forward as possible. this will allow taper in plan. 8' wide at the back of the load, rear axle width at the axle line and then you can increase as you go back from there. The radius for the transition from the cab should be greater than the depth of the transition, in other words, start at maybe 45% in plan.

Round back off the top of the windshield in plan or elevation, or both.

Make the bottom of the foldable tail separate and strong enough so you can use it for a back porch when your parked in the country.

If you use metal studs you can notch them to make curves. Turn them so they're 2" deep, not 4". that will gain 4" in interior space.

There have been discussions of rooftop blisters for vent/air conditioning, but I don't remember the thread. Maybe someone else will. I would recommend going through the Phil Knox seminars.

All above IMHO, of course.
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Old 08-30-2012, 05:11 PM   #3 (permalink)
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Ok, I did some photoshop to the template I found here.

This is a rough draft, I might still need to go slightly taller in the front, but I'm not sure yet.
The first shot is the RV as of now.
Then the first attempt at remaking it using the template.

The tail piece I showed would be only used while driving, then folded up for parking.

I was wondering if the bottom part could just be replaced with flat side skirts like semi's have, angled towards the rear wheels instead of doing a belly pan (might be a real pain for this... )
Anyways, am I screwed here, or does this look like something that could net some serious gains, along with motor diy (electric fan, electronic ignition, and electric fuel pump)



Last edited by capturedbyrobots; 08-30-2012 at 05:30 PM..
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Old 08-30-2012, 05:39 PM   #4 (permalink)
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Old 08-30-2012, 07:10 PM   #5 (permalink)
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being a 1972 is very nice, you can mod the engine/drive train in any way since your 100% DEQ exempt.

be a bit of work but swapping to a manual trans whould help.
also look in to how many gearing differences there where back then.

its likely geared like are delivery truck before we changed things up.
3sp auto and 4.11 gear makes for about 3,000 at 60.

if the engine is the 440ci swapping to a 318 would help as well.
i know more then one person that can get high teens out of a 3/4 ton with a 318 where the 440 is REALLY BAD MPG, LIKE 12 IN A EMPTY TRUCK
the 360ci gets about the same mpg as the 440 so i cant reccomend a 360 my self.

i do know one person that did a swap to a ford 6.9L with the ford 3sp auto trans and it turned in to a 9 to 13 mpg auto. it was 3.5 to 7.5 mpg with the 440
aro mods, diff swap and a manual trans would have taken it to the high teens or better.

an electric fan would be a good idea, unless it needs more cooling on a long grade do to being around 10,000lbs
clutch fans can take more btus of heat out of the coolant in less time then a electric, thus why big rigs still have them.


even if its a 440 and 3speed auto, getting about 6 mpg and you don't mess with that.
"MAJOR" aro changes should get it an avrege near 9 mpg at around 55mph
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i get 29/31 with stock drive train.
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Old 08-30-2012, 07:58 PM   #6 (permalink)
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Sorry, I wasn't specific of the powertrain.
360, stock holly 2bbl, glasspacks, 727 w/gear vendors under/overdrive, 4.10 rear,
Gear vendors chart shows that when the overdrive is activated it acts like a 3.2 rear.
I'm getting about 7-8mpg loaded to the hilt. I bet I could get much better mpg with less extra crap in the camper, and lots of aero changes.
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Old 08-30-2012, 08:03 PM   #7 (permalink)
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Oh, and 99% of my driving is freeway, I activate the gear vendors at about 45, and it carries me up to 70 + easy, but I usually keep it at about 60. Hums right along. Before I had the gear vendors, it was screaming at 55. that was some serious long drives when you max out at 55!
I don't know if a 318 would have the grunt I need for my load when hitting the mountains or extreme headwinds. My robots and amps and merch is about 1500lbs, can't get much less of a load.
And, the rv now is totally gutted, no appliances or holding tanks at all. Just a plywood bench seat and some 1/2in plywood walls and doors. The 1x2 framing and aluminum shell makes the body very light.

Last edited by capturedbyrobots; 08-30-2012 at 08:12 PM..
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Old 08-30-2012, 08:36 PM   #8 (permalink)
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looks like a good start, you can only go up from here

keep it up!
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Old 08-30-2012, 10:58 PM   #9 (permalink)
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bingo, gear venders that's the perfect thing for keeping it above 7 mpg and doing nothing else
3.20 gear is just right...
striped out im thinking it still something like 6,000lbs or so but that's just a gess...being a 1 ton chasse, your not going to get super light.

are you using a trailer for the cargo, or is it all in the RV

the 318 is just fine in my mind, it was a common gas saver 3/4, 1ton engine tell the 90s

in a way having the 360 is a good thing, even though i personly dont like them, the trans housing is the same as a 318.
where if it was a 440 you would need a trans swap or housing change.
so should you want to do that it would not be as hard as if it was a 440

i have no science to prove it. but i think with big aro mods, you can have the drag you had stock at 45mph at 60mph with a much better aro shape.


are delivery truck was a 460 and C6 i know all about a screamer engine and ""galleons per mile"" in the city WOW.
we swapped it out for a 300/6 and a early ZF 5speed truck does little freeway driving so we stayed with the 4.10 gear

is it fast, NO
loaded to 14K can it go faster then 70 at WOT on a flat road, NO
did it make the mpg of the auto 100% better YES
do the brakes last twice as long with the manual trans to help slow on hills YES
can it move the same loads it did with the 460 YES just a little slower.

granted we modded the engine for air flow so the engine could breathe much better. the old 4.9L I-6 had some really restricted air flow, and a EGR that was flat silly to even be there since it was just a pipe.
but did not do a cam change or drastically over sized carb


any way, sounds like your off to a real good start
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1 86 T\D trooper with rare GEN 3 rods TRANS FIXED NOW DD
1 86 4WD 5sp pup is 2.3L gas, but plan on 2.2L diesel repower
1 91 trop, long term plan is a group buy of imported Isuzu 4JB1-T 2.8L I-4 engines, hoping to get price down to 2K not 3K plus
1993 sidekick my MPG toy, epa rating 26.
i get 29/31 with stock drive train.
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Old 08-31-2012, 12:57 AM   #10 (permalink)
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Well, maybe once I have some aero mods, I could do a 318. As for a manual trans, I could do it, but the 727 was recently rebuilt.
What I'm hoping is that if I have success with a new body, and doing all the aero mods I can do, then I can see proof of concept which will spur me on to get crazy with this stuff on a better platform later.

Now to framing. I have a ton of redwood if I wanted to go that route for the beams. I could use conduit or steel studs, I'd use square tubing but that would get heavy fast. I just want the body to be as light as I can go. Would sheet metal riveted over a steel stud frame be strong enough?
I'd sandwich some sort of hardboard or thin plywood on the inside to add insulation and rigidity.

Just looking for someone who's done this before.

Then lastly, will the long angled descent across the roof help that much on aerodynamics (like in the template)? Why doesnt it show up on production bigger vehicles?

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