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Discussion Starter #1
I'm sorry if you're grumbling, "Not another 4bt vs 6bt post!" but I would certainly appreciate any input. I've got a 3/4 ton Suburban with a 383 stroker. I'm planning to convert it into a home grown pop top expediton/overlander (whatever name you like) RV. I'd be doing little if any towing, want the vehicle to get me to the tip of South America and back and then to Alaska. Financially, does it make more sense to swap a 5.9, 3.9 or leave the 383? Thanks so much.
 

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What condition is your 383 in?

Either engine (4bt or 6bt) will work but I'd be inclined to go with a 6bt since you'll have the room under the hood. You'll probably have a few lbs loaded for supplies so it won't be a light rig meaning you probably won't see a huge difference in mpg between the two (4bt or 6bt). For dependability a diesel would be better but you could probably find more places that carry parts for you chevy if you need repairs. Financially you could try calculating how many miles you'd cover on your trip (just a guess-timate), chose a couple of prices for gas and see what it could cost at your current mpg. Then weight how much you could find parts for (that means searching some for $$ on both setups, $ for engines, parts adapters, etc., basically plan out a swap), calculate your new diesel fuel costs on a few fuel prices and a few mpg figures and see how it stacks up to just using the gasser.

Now if you just really want a diesel, then none of this matters so start getting you parts and do a swap! :beer:
 

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I would go with a 4BT without any modifications for dependability and economy. The mileage benefit will show up when you start traveling for hours at a time over poor condition roads in lower gears.
 

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6bt. Yea sucks more fuel but I would think that the 4bt would be struggling over the hills and mountains that are in the US and South America.
 

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I have been very pleased with the power of my 4BT in my 'burb. I have propane injection on it, but it doesn't take much of it to really make the power good. I think it is more than adequate even at 75 mph in the mountains. It is a shoehorn fit to get a 6BT in a GM, especially a 4x4. To do it right, the trans needs set back 3" to get fan clearance.
 

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The 4bt will perform fine at anything under 10K. If your RV was 12-14K I would go with the 6bt. They weight less and are easier to keep cool. You can get an easy 150hp and 350lbft out of one with a governor spring and turbine housing. a cool 180-190hp with intercooler. I have finished 5 4bt swaps, and all have been in 3/4t rigs. I have pulled 20K with one and it did beter then a 454.
 

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The 4bt will perform fine at anything under 10K.
I agree completely. While I have never been in any 'real' mountains, I have towed partway through western Pennsylvania a few times with my trailer, and have only had to shift down out of 5th one time up one of the hills while westbound on I-80, into a headwind, with a GCWR of about 14,000lbs. The only mods to my 4BTA is 1 3/4 turns in on the full fuel screw.

In short, a 4BT will work great for you. Good luck!
 

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Discussion Starter #9
Based on my research thus far, I can't really see that the 4bt would be a cheaper swap than the the 6bt. Would you agree or disagree? Does the 4bt run rougher than a 6bt (I ask because I read a statement like that on some other forum)? 4bta is intercooled right, does this mean I can't just add an aftermarket intercooler and some custom piping to a 4bt without a whole bunch of other mods. I figure the 383 stroker probably gets about 300hp and close to 400torque at the flywheel. I'd be happy with that torque number, apparently I can expect 120+ hp @ 2500 rpm with peak torque of 327 lb-ft @ 1700 rpm. The engine weighs 570 pounds (dry). Can I get 17mpgs with a 4bt if my vehicle weighs 10,000; 12,000? Wikipedia says that a 5.9 12 valve will yield about 160hp and 400lb/ft of torque. Is this right? What's the weight of a 5.9liter? Again thanks.
 
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