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Discussion Starter #1
Hello everyone, first time posting here on 4BTSwaps. Long time lurker though. None the less, I am sure many of you are far more knowledgeable than be when dealing with a cummins lineup of engines. So I figured I would post a question here.

Currently I have a K5 (actually an M1009) with a 6.2 diesel. I plan to do a 14Bolt axle swap with perhaps 3.73 gearing (not sure, not important right now though). So that way the truck will have good axles to take some added power. :idea:

This brings me to my question. The K5 weighs 5200lb without anything on/in it. I want to do a 4BT/6BT swap, but I have some concerns. From what I heard AND seen, people have put a [mostly] stock 6BT in a K5 without boxing the frame but instead made very strong cross members. Good stuff, seems to hold up well, but obviously I am sure the frame doesn't like it much, but at least now you have some solid power under the hood. I was thinking about going the 4BT route since its weight is the same as a 6.2 diesel, but after reading the specs, it doesn't seem like it would be much of an upgrade in the power department. I thought about maybe building it up to get some extra torque and horses, but I just do not know if I can justify the costs yet. Which option would be best, and why? What route would you go with? :confused:

I am not looking for anything crazy powerful, but I do want my truck to be able to move out of its own way, travel faster than 65mph without slowing down to 45 whenever a small hill is encounters, and it WILL be overlanded. Not mudded, just doing to some trails that might have some steep inclines, so RELIABILITY IS A MUST. Some of these trips are exceeding 3000 miles at a time, so if the engine needs to be built, it will have to last.

TLDR, 6bt or built 4bt? Is a 4bt strong enough for a K5?

Sorry for the long post
 

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One consideration would be, are you going to be hauling any trailer loads? If a 6bt, you will need to upgrade the front axle, D60 would be necessary. Choose final drive (trans/diff. ratios for 1800 cruise RPM). If no jumping, etc., is an option, the stock frame should be adequate. 6bt's are generally more available, more economical.

Ed
 

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i have a 4bt in an overland mild offroad build. gearing is key 3.55 or lower (numerically) depending on tire size. If i build mine again it would be a 6bt basically free mods (low cost) give you way more power than you will ever need. the 4bt i'm pushing big boost studs non original OEM turbo to get almost the same power as a stock 6bt. which do you think will be more reliable long term? and when you look at cost of stock 6bt vs even a mild built 4bt a little frame reinforcement/weight management is not a big deal. really the 4bt pushed hard vs 6bt mild will net you about the same MPG. my buddy and I almost have identical rigs mine 4bt his 6bt. we're with in about 10% if not the Same MPG when we go out together for day trips with the kids. we compare EGT boost levels on very small Kansas Hills and i'm always 5-10 psi above him with EGT's about the same since i have an inter-cooler and he doesn't. and his has great power and quick for what it is. mine is still very acquitted don't get me wrong but no the same.
 

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Discussion Starter #4
I cannot see myself ever hauling anything as far as I am concerned, and I do not intend on putting my K5 through excessively abusive situations (flooring it, hopping, etc). But it will see some off road use, nothing over moderate levels. I will be doing that d60/14Bolt swap so no problems there. Thanks for the gearing advice, it is still up in the air, anything is possible. Now, the 6bt I agree is better suited in general for a heavier vehicle like mine. But the problem is I feel as though whenever you ask anyone about a K5 build, they all will yell at you to box the frame or how it just won't cut it. Who knows? They might be right. But I know some older mechanics that have seen it all in the GM world (some work for GM) and they all claimed it should be fine with another leaf in the front. But I worry about how the frame will hold up during off road use. That is why I was thinking the built 4bt route. I am only looking for mild-moderate performance upgrades. My engine was rated at 165hp and 330ft-lb of torque (which is strongly doubt I am getting). I just want to exceed that a little, just to justify the upgrade, while still being reliable. (oxymoron I know, but is it possible? Aftermarket piston rings, head studs, etc?). As for fuel economy, it really sucks that a built 4bt will be like a 6bt, but I do not know if my K5 can really handle a 6bt all too well you know? Got any more thoughts/suggestions?
 

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I have been running a 4BT in the 200+ HP range in my 8,000# F-250 started with the HE221 VE pump and stock injectors averaged 18+ MPG at 75 on the highway, at that level it beat the 390 big block in every way but I was working the turbo at it's limit. That being said I "drove it like i stole it" for close to 40,000 miles until the head gasket let go with 285,000 miles on the clock unloaded the truck would pull a 6% grade on OD at 70/75 MPH and i towed to a CGVW of 16,000# without being too slow.
Since the rebuild I have added head studs 5x.012" injectors and compounds Wh1c/44mm HX30 and have gained quite a bit of power at WOT but the biggest gain has been at part throttle,before it required WOT to pull a 6% grade at 75 = 28psi/1,150*EGT's now I see 32/35psi and 900*EGT's at part throttle, the 4BT seems much happier now doing the same task. I think you will find that the 4BT will perform very well on the type of trails you plan to run I spend most of my time on trails between 1,200 and 1,700 RPM with my truck's weight I don't do any high speed trail running and tend to use my 2-1 underdrive and 3rd/4th gear so boost is low 10/15 psi and EGT's around 600*/800* .
So if you plan to add a properly sized turbo/IC and fuel to match the 4BT should do the job you need.............$.02
 

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Discussion Starter #6
I see what you mean. As for the head studs, if I was going to work on building one of these, and I swap those out for some beefier studs and stronger pistons/internals, would you say that will be reliable still? I was thinking about pushing ~180HP. How bad were the vibration/noise in your truck?
 

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I do not see any reliability issues at the 200HP level as long as you do not overheat it keep the oil clean and allow the turbo to cool down before shutdown.
Also be sure of your pump timing BEFORE you advance it that bit me in the @$$In my mind most of the problems i have had in the last 5 years and nearly 50,000 miles were self inflicted :(
I will be the first to admit that I am guilty of running it harder and for longer times that i probably should,my rig really needed a 6 but it was too long and heave IMO for a '68 F-250 and a shorter interval between overhauls is the price i will pay for a foot shorter and 400# lighter engine...........Every build is a series of compromises that must be weighed against each other as it is between the 4BT and my winch I am carrying ~4,500# 0n the front axle and i wish it was less now .........
 

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Yikes man, but yeah, definitely compromises have to be made in almost every department. When looking at upgrading to 200HP I hear that head gasket issues begin. I definitely would swap out the head studs for something stronger, but what other upgrades do you think are worth looking at/buying to make 200HP possible? I am not new to diesel, but I am new to Cummins. I know that they have so many goodies to play with compared to many other diesels. Oh, and one last thing. Is it better to get a re manufactured one, or just get a running one and overhaul it entirely?
 

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I got there with a turbo either the He221 or one of the HX30's a 3,200 governor spring and a large IC the rest was just tuning the pumps advance and fueling to use the air that the turbo upgrade provided.
200HP can be reached with less than 30psi so unless you run too much advance the stock gasket/bolts "should" be fine.
I focused all my mods to play on the b series strength which is between 1,500 and 2,000 rpm, to me the only real advantage to the 3,200 spring over the stock one is that it starts to defuel later not not because I wanted to spin the engine any faster. I never spin faster than 2,600 RPM and that only happens in the lower gears the 3,200 spring will still deliver full fueling at those RPM's the stock spring would already start defueling by then.
I would be hesitant to pay the market price for a used one today UNLESS it was in a van I could drive,it's too much of a crap shoot to pay top dollar for a "good running" engine that is on a pallet I know people that got what was represented to them and people that got hosed, by the time i rebuilt mine between machine shop labor rebuilding head, surfacing,boring/honing block and reconditioning the rods plus quality parts not a "budget" chinese master kit i was in over $5,000! but it runs great and is much smoother/quieter that the 200,000 mile engine I took out of the bread truck.so the price of freshly rebuilt 4BT's is not out of line IF it's a quality rebuild with quality parts.
 

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Sounds solid, I appreciate the detailed reply. I will keep this in mind if I decide to go the 4bt route. I am also considering a 6bt. I actually work for a diesel company specializing in generators and we used to deal with the 6bt actually. From my documents, it says that a 6bt should clock in at 950 lbs. Now the thing is that a 6.2 diesel clocks in at 750 lbs. So that is only a 200lb difference. What I just don't understand is if everyone is scrambling to reinforce the frames of their trucks so a K5 or 1/2 ton can take the abuse of 6bt, what is the difference between that and having a big snow plow in front of your truck with the 6.2? Do you think a 6bt is a legitimate swap idea? (Assuming d60/14 bolt swap and strong crossmember?)
 

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I wouldn't want a 6BT in a Blazer that is just me there are many people running 4BT's in Jeeps/landcruisers and other mid sized vehicles who are very happy with the combination.
I had planes to do a diesel '67 wagoneer and was planning to do a compound turbo 1.9l TDI and a close ratio 6 speed because I did not want to lift it enough to fit the 4BT and did not want it to be nose heavy.
I want a vehicle to have decent front to rear weight distribution for safety and handling purposes and would rather work a smaller/lighter engine harder or do with less power and make it up with transmission gearing,but that is just me and I'm a bit OCD about not stacking the deck against myself when some fool cuts me off in traffic or a damn elk runs out in front of me on some two lane mountain road.
 

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I cannot see myself ever hauling anything as far as I am concerned, and I do not intend on putting my K5 through excessively abusive situations (flooring it, hopping, etc). But it will see some off road use, nothing over moderate levels. I will be doing that d60/14Bolt swap so no problems there. Thanks for the gearing advice, it is still up in the air, anything is possible. Now, the 6bt I agree is better suited in general for a heavier vehicle like mine. But the problem is I feel as though whenever you ask anyone about a K5 build, they all will yell at you to box the frame or how it just won't cut it. Who knows? They might be right. But I know some older mechanics that have seen it all in the GM world (some work for GM) and they all claimed it should be fine with another leaf in the front. But I worry about how the frame will hold up during off road use. That is why I was thinking the built 4bt route. I am only looking for mild-moderate performance upgrades. My engine was rated at 165hp and 330ft-lb of torque (which is strongly doubt I am getting). I just want to exceed that a little, just to justify the upgrade, while still being reliable. (oxymoron I know, but is it possible? Aftermarket piston rings, head studs, etc?). As for fuel economy, it really sucks that a built 4bt will be like a 6bt, but I do not know if my K5 can really handle a 6bt all too well you know? Got any more thoughts/suggestions?

Compare the frame of a Dodge with a Cummins with your K5. If they look about the same go with the 6bt.
 

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There is a good buildup thread with a 4bt in a crew cab, short GM pickup with px and U-Tube videos, might give you good ideas about fits, etc.

Ed
 

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I put a 4bt in my 77 RC. I think If I had to do it all over again, and with what I know now, I would have found a 91.5 thru 93 Dodge donor truck and swapped all the needed components into the RC. I feel that the 4bt in stock configuration is under-powered for a full sized heavy vehicle. Which is fine for a stepvan hauling bread or chips. I've already done the 366 spring swap and turned up the fuel screw. While it did enhance the performance a little bit, it's still under-powered. However, that's with the stock baby H1C turbo. I'll be upgrading to a HX30W turbo soon and hoping that the new turbo really increases the performance that people swear on.
But, even with the first gen 12 valve with VE pump, that power is already there in stock form. That's my honest take on the subject.

Mike
 

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Sounds solid, I appreciate the detailed reply. I will keep this in mind if I decide to go the 4bt route. I am also considering a 6bt. I actually work for a diesel company specializing in generators and we used to deal with the 6bt actually. From my documents, it says that a 6bt should clock in at 950 lbs. Now the thing is that a 6.2 diesel clocks in at 750 lbs. So that is only a 200lb difference. What I just don't understand is if everyone is scrambling to reinforce the frames of their trucks so a K5 or 1/2 ton can take the abuse of 6bt, what is the difference between that and having a big snow plow in front of your truck with the 6.2? Do you think a 6bt is a legitimate swap idea? (Assuming d60/14 bolt swap and strong crossmember?)
K5 frames suck, the 87 I am putting a 6bt into the frame mics out at .150. Essentially, an open 1/8 channel from front to rear that was barely adequate for stock use. That said, it is not going to turn to dust the instant you mount a 6bt in there. Some folks don't mind fixing and repairing cracks as they occur, others like to nip them in the bud before they start.

As far as 4bt vs 6bt, a 6bt fits fine, it is a much better bang for the buck, and if I do an engine swap---I want to feel extremely happy with the power and economy. If handling/ off road performance were your main goals, I would suggest putting a built small block in. If highway drivability, torque and economy are the goals, the 6bt looks pretty attractive compared to some of the options.
 

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I'd say you've got some great advice here. The general idea is either engine will fit and has been done. The 6bt engine alone will cost less and 4bts are getting more scarce. A well tuned 4bt would be more like you'd put a 454 big block in compared to the 6.2. A 6bt would need very little tuning to get to the 200 HP or higher level. Since you're going for stronger axles, I'd say do some frame reinforcement too. I believe Rube Bonet makes some kits for that as long as you have some welding skills. When it comes to the engines, never assume it's a good one unless it comes with a warranty. Plan on at least new seals and gaskets and a general inspection of the internals. A $1000 is a beginning point and can go up from there. Head studs have been mentioned and are not a bad idea or extremely expensive. New rod bolts will be required if you inspect the rod bearings. Might upgrade there too. A lot of the cost can depend on how much work you can do yourself. The two big ticket items on these engines are the injection pump and turbo. Those are also what creates most of the power. You mentioned axle gear ratio and the best advice is figure what size tires you want and compute what it takes to keep the RPM in the 1800 range. Also, have to decide on what to do for a transmission. Will it be automatic or manual. Most of our members use manual but automatics can be done too. Be looking forward to seeing your build and don't be afraid to ask questions. Lot of info and knowledge on the forum.
 

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I had a 4bt in my 78 K10 shortbox. 3.73, 33 inch tires, NV4500. Had VE pump and 44mm HX30. It ran awesome. The pickup was pretty clapped out so a junked it this summer. Bought a K5 blazer to put the drivetrain in. I can't think of a more ideal set-up. I don't have it swapped over yet, but the power should be perfect for a K5. K5 doesn't have enough wheel base to make a real heavy tow rig anyway. I would think the weight of the 6Bt would be as much of a disadvantage in something as small as a K5.
 
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