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Juggernaut
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37 Posts
Discussion Starter #1
Ok, I’m always getting so many questions about this subject. Obviously many of you are interested in doing such a conversion so I decided to write this thread about my own personal experience so that everyone can have one thread to reference back to in the future.

My 2005 Cummins had an injector failure which resulted in #6 piston being damaged so after removing the block and examining what damage had been done I decided to try something different. I started doing my research in my 6.7 manual and comparing everything to the specs on my 5.9. As far as I could tell there was no reason I couldn’t find a 6.7 bottom end and use my 5.9 head and electronics. At this point in time I couldn’t find anyone who had done this conversion. Google searches turned up nothing and everyone was telling me that it wouldn’t work. I build engines for a living, mostly class 8 truck engines but we do a lot with the 5.9 and 6.7 Cummins as well so I had a lot of spare parts at my disposal to make everything come together. It’s been a couple of years since I did this but I will try to remember everything to the best of my knowledge.

I started with a 2008 6.7 Cummins and a 2005 Cummins. We stripped both engines completely and performed all necessary machine work to the 6.7 block and to the 5.9 cylinder head. I wanted to continue to use my 5.9 head because of all the work I have done to it (bolt on intake, ported and polished, etc.). The blocks do have some differences but nothing that is a real issue for doing the conversion. Just make sure to use a 6.7 head gasket !!!

At this point I think I should make it clear that I used only the 6.7 block, crank, oil pump, pistons and rings. Everything else is from my original 5.9. That means I used my 5.9 front and rear housings. This is important when it comes to the clutch/flywheel you are going to be using. The oil pump is different from the 5.9 to the 6.7 and since I used the 6.7 block I had to use a 6.7 oil pump. Obviously I installed a new oil cooler but I don’t believe there is a difference between them.

You guys can see from my signature the components I chose to build my engine with. They work very well and I have no regrets about the path I chose. I did not have any issues with motor mounts, bell housings, cylinder head or anything else bolting to the 6.7 block. Everything was in the same location. I did not have any issues with connecting rods hitting the camshaft and I did not do anything with the coolant passages in the 6.7 block. They are simply blocked off by the cylinder head. I used injectors for an 03-04 Cummins because the most closely resembled the spray pattern/ bowl design. All electronics bolted right on and everything worked perfectly!

So, I hope I have answered most of your questions. I really encourage anyone that has been thinking about trying this to give it a go. You will NOT be disappointed! I’m sure I probably forgot a thing or two and might have to come back and edit this post later but if anyone has any questions or concerns please do not hesitate to ask. Thanks !!!
 

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108 Posts
Subscribed. Very cool project! Any pics handy? How does it drive and perform compared to a similar 5.9 and 6.7?
 

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Juggernaut
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37 Posts
Discussion Starter #4
I'm sure I have pics somewhere. I'll see what I can dig up. Don't really look any different than a 5.9 tho. lol It drives perfect!! Can't ask for anything better, especially on the bottom end it feels like so much more than my 5.9's!
 

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vvv SOME PEOPLE'S KIDS vvv
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11,153 Posts
Yea basically you used a 6.7 bottom end and through a 5.9 head on it. The rods are the same length. This is nothing new.. It something I've been pondering upon for quite some time. Just gonna take some time.
 

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Diesel sniffer
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3,805 Posts
Exactly. Its like using a 6.7 CP3 on your 5.9 and calling it a stroker pump.
 

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It worked out well for the OP with the parts at his disposal. I pondered it, also pondered a 6.7 crank in my 5.9 (stroker). Then it's custom pistons.
The cost is just crazy though. The bottom end is expensive, everyone wants an arm and a leg for the short blocks.
 

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World Champs!!!
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24,829 Posts
Well, he's right. Dropping a 440 in place of a 400 doesn't make it a 400 stroker...

That said, I agree. Great swap. I get pm's on a nearly weekly basis about my swap, which is great; tell every one of them it's worth it. The torque down low is very noticeable, and I'm still on stock fuel. My 07 is slated for a billet-rodded 6.7, but that's years down the road. Unless I pop pistons again
 

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109 Posts
any Mileage Reduction With 6.7 short Block?
 

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World Champs!!!
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24,829 Posts
I haven't seen any decrease in mileage. And any decrease there might be would be strictly because I find myself romping on it a bit more
 

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Juggernaut
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37 Posts
Discussion Starter #14
I posted this only because so many people had questions about doing it. If they do or not I simply wanted this thread to be somewhere they could reference back to in the future. But somehow everyone feels it is more important to play on the words that I chose to title it as ?! Do you think I don't know that it's no longer a 5.9??? I was only trying to make a contribution to this site but whatever, guess it is what it is.
 

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vvv SOME PEOPLE'S KIDS vvv
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11,153 Posts
Maybe you can get a moderator to change the title to "6.7 short block with 5.9 head"... or something within that line.
 

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maybe everyone should stop being so picky.

nice writeup dude! maybe one day i can afford to do that swap
 

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smokinpete379, What damage was done to your original 5.9 block? Im just curious to why you didn't buy the 6.7 crank and throw it in instead of buying a whole 6.7. Which way do you think would be cheaper in the end?
 

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World Champs!!!
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6.7 crank in a 5.9 block yields 371 cubic inches; the added cost of custom pistons (I believe) doesn't make it feasible.
 

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ok so did you use the 6.7 rods or aftermarket? and is there any diferance in the topends ? is a 6.7 head better than a 5.9 ? (i know yours was ported ) i see you also installed a hamilton cam (i'm sure that helped ) along with the other goodies .

i would love to add some bore and stroke for the added lowend !!

can you buy new shortblocks ? how bad would the price be ?
 
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