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Old 03-16-2011, 09:56 PM   #1
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Default Blizzards cab to box wall

Rather than hi-jack the other thread I'll answer your question here,

My cab is bolted through the floor solidly to the frame via the big sheet steel that serves as my inner box liner too. 5 bolts 6" apart. front to rear both sides

the "over the cab box" was welded solid to the roof steel, then the roof of the cab was cut out.

the two angle sheets on both sides are welded solid to the cab walls the front step sheet and the tubing for those walls placed at both the outer sections which are tied together across the top.

the structure of my basement storage box area is very rigid, not much flex in the frame anywhere, so all the work is done with the springs, like a well built race car.

I haven't noticed any thing negative yet, most motor-home campers are attached solid to the cab, go to a rv store and check it out. I hope not to ever have to off road it mush more than a campground spot, and then I will be very gentle and with my low ground clearance I'll try not to hang it up on a high spot or twist it to the point where I have to worry about things like the windshield cracking, which I think would be my weak spot.







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Old 03-17-2011, 10:36 AM   #2
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Blizz-

Thanks for the response. Sorry about the other thread, I am new at online forums and am not familiar with the etiquette on hijacking a thread. Now I know.

I don't remember seeing that side view on your frame when looking through your build, I think most of the pics were close up inside the building. I did not realize those side plates went that far up under the cab. Bolting the cab solid to the frame makes perfect sense, sometimes I think too hard and ignore the obvious. I could easily eliminate the rubber mounts and fab some brackets to bolt the cab solid to the frame. Also ignoring the obvious, I should have taken a cue frame class c motorhomes there instead of just the toterhomes I've been getting ideas from. The only factory toter I've come across with a roof cutout was the Pony Xpress, but that's a lighter duty unit on a 5500 chassis with only an 8' box so they probably don't get much chassis flex.

http://www.hgrstrailer.com/pdf/pony_.../toterhome.pdf

I can't imagine those rubber mounts do much for ride quality anyway, but my truck does have leaf springs and not the luxury of your air ride. Maybe I'll need to scrounge up a a pair of air ride seats at the local truck junkyard.

Thanks again for the help!

Dave
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Old 03-17-2011, 11:22 AM   #3
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If you get air ride seats, make sure they are from a GMC6500 or f650-750 style truck, the regular HDT air rides are to tall. our steering wheels are much lower as they are in that pickup cab dash.

before you start, make sure you like the gearing on your truck too. take it out on the highway and run it up to speed, see how it runs, it is much easier to change ratios or tire sizes now, rather than after you have built a box atop it.

blizz
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Old 03-17-2011, 01:36 PM   #4
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Gearing should be good.

I'm towing my 40' trailer with a Chevy dually now (8.1 gas, 4.10 gear) and it has more than enough power but could use 200-300 more rpm to be absolutely perfect on the highway. I like to run 68-69 mph (we're still 65mph for the most part back east) but the truck likes 75 mph way better. I can actually hold speed on grades at 75 that bog me down at 65-70. Anyway, I did the math and the new truck has a 5.57 gear and low pro 22.5 tires, and it comes out to right at 200-300 rpm more than I am pulling in my current truck, so it should work out perfect in theory. That is figuring from each trucks 1:1 gear, 5th out of 6 on the dually and 4th out of 5 on the allison in the 6500. Same 8.1 gas motor in both. Plus we drove the truck home from Wisconsin to eastern Ohio and it'll hum along nicely at 75 in overdrive without straining the engine. So I think I am good. Excellent advice though, I have seen other guys on the forum fighting gearing issues. And you are right, it is sure easier to change out the pumpkin when I can just back the chassis under the shop hoist instead of manhandling it on a creeper. That is the one problem I can see with your truck, I pity the guy that has to work on the drivetrain when something breaks. You're gonna need one of those old fashioned semi shops with a pit to do any work under there. I think I'd have built a taller garage instead. lol. It was a Schwann's truck, so I guess they must do more country miles than city so the gear the trucks differently than a ordinary delivery truck.

I know all you diesel guys are cringing at my choice of a gas motor, but I think I am going to be fine. Pulling the same trailer right now with the same motor in my dually, with power to spare. I can pass semi's up a grade all day long. I know the 6500 is heavier, but I figure between the extra power I have now and the better gearing I should be just right to pace the big trucks, and I'm not generally in a hurry anyway. Couldn't pass up the deal on the chassis. 2003 GMC 6500 in real nice shape and reasonable miles for $4800. Ex Schwann's ice cream truck, so it runs on propane which is not a big deal here as our family business was propane and we have run countless vehicles on propane over the years. Great for engine life, runs like brand new. I can hold 160 gallons of propane, so won't have to fill up often and every Flying J has it, generally a little cheaper than gasoline.

Once again, thanks for the advice.

Dave
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Old 03-18-2011, 03:06 PM   #5
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Hot rod - I'm sure you realize that the 8.1's in MDT's aren't running the same HP & TQ as the engine in your dually.. not to mention the propane engines typically are tuned for less power than that (less BTU's/gallon, etc.)

What's the engine in the 6500 rated at?

(I have an 8.1 in my Avalanche and really like it even at 14k gross, but at 23k gross or so, it's gonna be foot to the floor and 40mph on any hill - a guy has the same truck as me and pulled that load and that was his report, with the better aerodynamics of no big box on top)
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Old 03-18-2011, 05:07 PM   #6
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Eskimo-

I'll have to check into the rating on the 6500. I know my 8.1 in my 2001 3500 was the first year for that motor in the duallies, and is not rated as high as the newer 8.1's, I think 290hp off the top of my head.

The power level of the propane vs. gas does not bother me, propane was our family business and literally the first thing I ever drove was a Wheel Horse with a bbq tank on the back, and have run everything you can think of on propane, from cars to mdt's to race cars. It's 108 octane and tuned properly can outperform gasoline. The problem is nobody knows how to tune properly. You are correct on the lower btu's per gallon, if memory serves it's in the neigborhood of 98,000 btu per gallon vs. 114,000 btu per gallon on gasoline. You have to burn a little bit more of it to produce the same power so mileage can be down from gas, but again good tuning can minimize that. The lower btu's hurt the mileage, not the power. I will admit this GMC is the first electronic direct port liquid propane injection engine I've had. Everything else has had a carburetor. I understand that the system on this truck uses the oem computer programming (gas), but these computers can certainly be reprogrammed easily. I am doubting there are any mechanical differences between the 3500 and 6500 8.1's in stock gas form, probably just the programming and/or injectors. All of that I can work with.

The truck could be switched easily back to gasoline, all it requires is the fuel rails, injectors and fuel tank and pump, but I like the propane, and I still have friends in the business and can buy fuel at wholesale. Last fall when we brought the truck home propane was $2.79 at Flying J when gas was $2.89, but I bought it wholesale for $1.89 per gallon. So even with a lower mileage I will be way ahead in the $$ per mile. With 160 gallons on board I can do most of my round trips without refueling on the road.

So I guess we won't know until I actually hook a loaded trailer to it and run it up a grade. Seems to run as well as the other truck now, but you can't tell a lot empty.

Thanks for the advice, I am actually impressed that you have some knowledge of propane, most people only know it can cook your burger.

Thanks! Dave
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Old 03-22-2011, 09:59 AM   #7
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I ran my rock buggy's old SBC off 'pane for a few years, using the standard Vff30 / Model E / Impco 425 on a q-jet baseplate & forklift tanks, and then re-curved the distributor advance to take advantage of pane's burn characteristics and get some power back. (Didn't bother upping the compression since it was a throwaway engine) I later upgraded to a more modern engine and now run EFI gasoline though, since it came with the engine.

I didn't realize they are using port-injection with 'pane - that's too cool!! My buddy that runs a dyno tuning business would LOVE to get his hands on that!
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Old 03-22-2011, 01:15 PM   #8
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Eskimo-

Yeah, everything back in my day was model E and 425. And that sure is perfect for your crawler, dry fuel into the engine, no float bowls, it would literally run upside down if it had too. (well, at least until the oil ran into the top end, lol) My favorite motor was my 427 big block in my daily driver street pickup. 13:1 compression, way too big of a cam, tunnel ram w/ dual 425's and dual model e's. 46 to 48 degrees total timing. ran smooth as glass, idle in traffic and 12.0's at the track in a full size long bed truck with no lightening and street tires. And that was back in the day when a 12 second street car was fast. Compression and ignition timing (and curve) are the secrets to making power. I'm still a little suspicious of the liquid injection on this truck, we used to figure a drop of liquid in the cylinder meant a shattered valve, but apparently they have worked that out, must vaporize right at the nozzle. It uses what has the appearance of a racing type billet fuel rail with special injectors that look similar to a gas injector, and an internal fuel pump in the tank. Schwann's puts millions of miles a year on them so I guess it is trouble free. We'll find out.

Here is a link to the mfgs website:
Bi-Phase Technologies - Using Propane for Alternative Fuel
they are now owned by schwann's

I'm doubting my top kick is going to fit your buddy's dyno, but I would sure be interested as well. Back in my day it was all trial and error with the timing and advance curve in the distributor, I think you could really optimize the fuel with todays computer reprogrammers if you took the time to experiment.

Dave
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Old 03-24-2011, 02:21 PM   #9
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Quote:
Originally Posted by hot rod View Post
I'm doubting my top kick is going to fit your buddy's dyno, but I would sure be interested as well.
Dave
He's done dually's before, and the dyno is built into the shop floor. Come on up to central PA! Worst case we pull the outers off.

(Not to hi-jack the thread anymore, but yes, it did run just fine while sitting on the bumper, on its side, and on its roof. but yeah, the oil pressure gauge pegged at zero told me to shut 'er down. )
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