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Old 09-07-2007, 07:57 PM   #1
streetstar
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Cummins 4bt conversion

Someone started a diesel thread in the 67-72 section and it turned into a Duramax vs. Pstroke vs. Cummins bashfest

I am just curious how a 4bt works in a full size truck or Blazer --- some of the jokers on ebay claim a conversion gets 35 mpg, but then i thought, if that were true - a lot of people would be doing it.

Because my ultimate goal for my Blazer is as a work vehicle with covered storage (not a tow vehicle though) - the mileage would be great even if it was slow

If your basic engine costs $3000, more or less, what other costs are involved? Everything i have ever tried to do to a vehicle winds up costing way more than i anticipate it seems

The hp rating on these varies depending on the model, but seems to top out at around 140, not too sure about the torque, but if its not over 400 ft/lbs, a stout 700r4 should be do-able if there is an adapter for it.

The big sixes are too long and the 6.2 and 6.5 Chevys just dont knock down mileage numbers like that
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Old 09-08-2007, 12:39 AM   #2
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Re: Cummins 4bt conversion

4bt's are strong little engines. Actually they aren't that little. Think of a 5.9 with 2 cylinders missing. We used to use them in Step vans, but I can't remember mileage numbers though. 35 mpg seems very optimistic to me. I'm thinking low 20s in a heavy truck.

Diesel Power magazine has an article on a 4bt conversion in an early bronco with some pretty good details.

One thing I can think of is if you get one from a step van application (GM or Workhorse) they should have the adapter to bolt up to the Chevy bellhousing pattern.

Don't overlook the 6.5's. They can be built with some better than stock numbers and still get mpg's in the low 20's. There are some good sources on the web for the 6.5's too.

Each has pro's and con's it's up to you.
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Old 09-08-2007, 01:59 AM   #3
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Re: Cummins 4bt conversion

My friend has a 4BT Frito Lay truck (14 foot box), and I think he gets about 20 pushing gobs of air.
Its a little slow, and a gear splitter would help it a lot.
He does get substantially better mileage than my 6.2 turbo 4x4, his manual 4 speed vs my TH400 may be a factor.
Best torque I have heard from a 4BT is about 700

You might end up about like this?
http://forum.ih8mud.com/showthread.p...ferrerid=15458

http://www.youtube.com/watch?v=l-YgVTgAasE
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Old 09-08-2007, 06:18 AM   #4
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Re: Cummins 4bt conversion

Its a great engine, the swap can be done and it will be really cool.

Remember, unless you are going to be doing the swap for the "coolness" factor, driving the heck out of it, using it to haul or as a work truck..........the initial cost, work involved and diesel prices will probably never offset the initial cost of the swap.

Unless you use them to work......diesels are NOT cheaper.
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Old 09-09-2007, 11:13 AM   #5
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Re: Cummins 4bt conversion

Hey freak, thx for the input --- i know a diesel swap is a bit spendy, but i think i can use it.

I am a catastrophe insurance adjuster and i put about 45 - 50k a year on my vehicles. My latest is a new F150. Like all new trucks, it is nice, but i am bored with it and when i am home i have really enjoyed driving my old Blazer.
I have been looking at new Tahoes to replace my Ford because of the lockable storage space, but an old blazer has that too and gives me more personal satisfaction to drive -- plus i wouldnt hesitate as much to drive over downed telephone poles, trees etc when i got to a disaster site. Plus - its a tax write off.

So my tentative plan (everything for me depends on how the wind blows - literallyand financially) was to buy a cleaner Blazer than the one i have and then do the swap. Nothing wrong with my current one, but its kind of high mileage and in need of a pretty spendy paint job and some interior work (it only cost me $2k so what did i expect)

I know that sounds like a high dollar operation to buy a 5 -6k Blazer and then do a 4 or 5k engine swap, but when you compare it to spending 30k (or more) on a new Tahoe, it adds a new element to it.

Another bonus, on top of better fuel mileage, is that the last couple of major coastal storm events i went to, there always seemed to be major lines for gasoline, while the diesel pumps were always open.

If it sounds like i have already talked myself into it, well, i have. Now all i need is a hurricane or earthquake to go to to justify it now. That and a little more direction in what would be the best engine for the swap.

I know Chevys put diesels in these for a few years, but the Cummins 4 seems like a more compact package if it does everything i need. Hopefully that means an easier swap and easier maintenance on down the road

Last edited by streetstar; 09-09-2007 at 01:52 PM.
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Old 09-09-2007, 07:30 PM   #6
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Re: Cummins 4bt conversion

The big sixes are too long and the 6.2 and 6.5 Chevys just dont knock down mileage numbers like that[/QUOTE]

and they won't last 500K miles. I actually met a guy last year with a SWB chevy and 4BT. it had the stock 3.08 rear and a 700R4. he said 26-28 faithfully if he stayed out of it and he had it bumped up a bit . if yoou get one with the old VE pump on it a few turns of ascrew can double your power, seriously, w/o affecting mileage too much. His truck was running low 15's that day in the 1/4 mile. the 4BT is a 3.9L, supposedly weighs about what a BB chev does. I LOVE the idea.crossy
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Old 09-09-2007, 09:58 PM   #7
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Re: Cummins 4bt conversion

4BT and a 700R4 ? Hope that transmission has been built to handle that kind of torque.
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Old 09-10-2007, 04:44 AM   #8
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Re: Cummins 4bt conversion

I've been wondering the same for my next project.
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Old 09-10-2007, 06:17 PM   #9
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Re: Cummins 4bt conversion

Quote:
So my tentative plan (everything for me depends on how the wind blows - literallyand financially) was to buy a cleaner Blazer than the one i have and then do the swap. Nothing wrong with my current one, but its kind of high mileage and in need of a pretty spendy paint job and some interior work (it only cost me $2k so what did i expect)

I know that sounds like a high dollar operation to buy a 5 -6k Blazer and then do a 4 or 5k engine swap, but when you compare it to spending 30k (or more) on a new Tahoe, it adds a new element to it.
Just to save time and frustration, why not look for a clean low mileage K5 already equipped with the 6.2? Take stock of the condition of the 6.2 and if need be replace it with a newer 6.5 with the manual injection pump. If you want the turbo, buy the Banks Turbo kit for it. Reason beaing is the 6.5's do hold up better than the old 6.2's as the manufacturing process got better as they went along.

As far as mileage goes, it should already have the 700r4 with it so there is your needed OD gear. Since off road won't be a major priority, gear it for the highway and run stock size tires. If you can keep your foot out of the turbo, low to mid 20's shouldn't be too hard to attain.

On the plus side, it would neen zero fab work. If you find a clean low mileage example you might be able to get in and go without doing much more than upkeep. Then you can add the 6.5 or 4bt later.

Lots of info to be had here: http://www.thedieselpage.com/

It's all up to you. I look at the easy way. Why spend a ton of money to make a diesel blazer when it's already been done? Granted, 6.2's and 6.5's have a bad rep, but most of those issues are addressed by the above website. A 4bt would beat a 6.2 as far as longterm durability, but how long would you need to drive it to recover the cost?
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Old 09-10-2007, 07:28 PM   #10
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Re: Cummins 4bt conversion

I like everything Rob Z. said to you, the main thing is finding a clean body. If it already diesel powered then it's a plus and makes the swap easier. a 6.2 or 6.5 is never going to get anywhere near the MPG of a 4BT. I dont want to get into a CUmmins Vs. 6.2/6.5 debate either. I am a member of two Cummins forums and it amazes me the poor condition of some of the trucks that the guys still love to death. Prices on diesel powered trucks and SUV's are on the rise though. crossy
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Old 09-10-2007, 07:57 PM   #11
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Re: Cummins 4bt conversion

Quote:
Originally Posted by Zoomad75 View Post
Just to save time and frustration, why not look for a clean low mileage K5 already equipped with the 6.2? On the plus side, it would neen zero fab work. If you find a clean low mileage example you might be able to get in and go without doing much more than upkeep. Then you can add the 6.5 or 4bt later.

It's all up to you. I look at the easy way. Why spend a ton of money to make a diesel blazer when it's already been done? A 4bt would beat a 6.2 as far as longterm durability, but how long would you need to drive it to recover the cost?

I thought of that and that would definitely be easier , but good diesel Blazers are as rare as chicken's teeth it seems. Granted, i have only been hardcore about the project for a relatively short while, so i have only been looking for about a week. Cherry gasoline powered donor vehicles to start with can be had for 5 to 8 grand though.

When it comes to recovering the cost, i am not as interested in that as i am in having the best vehicle i can for my money if i am already spending that much on it anyway. I really wanted to start with a nice first gen Blazer,--- but thought better of it when i thought of subjecting it to 45k mileage a year and using it in a storm environment.

I am not a billionaire playboy or anything, and am totally into doing it cheaper when i can, but as i said, the survivor Blazer diesels are hard to find (or maybe i am not looking in the right spots) ----- when the time comes to get serious, i will probably sell my late model to fund it
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Old 09-10-2007, 10:35 PM   #12
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Re: Cummins 4bt conversion

I kind of figured cost recovery might not be high on the list. Still, there are some decent 6.2 blazers out there. 5 minutes on autotrader found a pretty good prospect by the description:

http://www.autotrader.com/fyc/vdp.js...=&cardist=1391

It's in florida, but i'm sure more are out there. Even so, going with a 4bt is certainly an option if you can fab it up. Here's a thought as far as motor mounts go. Try to get the mounts and the engine cross member from a 4bt equipped chevy p-chassis step van. Reason being is that the front half of the frame on the P-chassis is very similar (if not the same from what I've been told) to the 73-87 as they came out at the same time. You should be able to literally bolt in the mounts with little to no fabwork at all.

Frito Lay was one of the big users of the p-chassis with the 4bt so thats a good place to start looking. One thing though, those things don't die. Up until recently Frito actually rebuilt every step van in its national fleet on a regular schedule. (something like 5 years or so- can't remember). Since the aluminum bodies didn't rust they basically replaced everything in it but the frame. New suspension, engine, trans, brakes, axles and so on. Frito usually rebuilt them at a location in Dallas TX. They might be a good source for the used parts or at least where they send the old ones to the graveyard to obtain the x-member.

Frito is getting out of step vans and not rebuilding them in order to go to a more "throw-away" fleet. Meaning, they might be selling off the old stuff as it comes to the end of it's life cycle. They might only do this in Dallas or at main distribution centers in other cities. I don't know. But it might be worth checking into to make the conversion a little simpler.
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Old 09-13-2007, 10:31 AM   #13
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Re: Cummins 4bt conversion

Interesting on the mileage. 22+ should be very do-able in 6.2. And I was getting 19 with my L6 250 in the 70's, with no overdrive. I gotta agree that it would be a sweet swap though.
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Old 09-13-2007, 09:28 PM   #14
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Re: Cummins 4bt conversion

Well, after a couple of days of study and research (in spare time - not complete days) -- i am completely overwhelmed with 4bt information for my idea and my brain is fried. At least i have a really good idea of what it is gonna take to do this now.

Now comes the hard part --- waiting around for a big storm to come along so i can get deployed with my job. A project like this isn't worth it to just drive 20 miles a day around my hometown, and i am hesitant at this juncture to sell my late model to dive into an empty pool. There is a company in Pennsylvania that advertises engines on e-gay that advertises that they will do the swap for a grand -- torque converter has to be changed to the diesel type for it to work, among other things -- At least i know now what i will be getting into-- still no luck finding a factory diesel model with less than a couple hundred thou on it. Anything with that kind of mileage more often than not needs a full restoration.
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Old 09-14-2007, 01:11 PM   #15
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Re: Cummins 4bt conversion

I have an '84 Chevy K10 with a 6.2 and 700R4 and it has got as good as 26mpg on the highway. They won't get that with a 3 speed auto though.
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Old 09-14-2007, 01:18 PM   #16
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Re: Cummins 4bt conversion

BTW, if you are considering a 6.2, they can be bought very reasonably due to the military refurshing the Humvees. There are literally thousands of them on the market right now that can be bought cheap. There's a guy in Mobile AL that sells them for $1000. He buys them from the military after a contractor removes them. He says that basically all of them are unloaded and driven to where they are going to be taken apart. He puts them on a test stand, and runs them up to temperature to insure they don't have a cracked head or blown head gasket. He said they are on average 10 - 40K mile engines.
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