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i know this has been asked a bunch but I have never found an answer that satisfies me.
My plan is to build a 12v to 700+ horse. Really aiming for 800+.

I know an auto would be all around better at holding power but, I want a manual as this is just a street/show truck.

Which manual trans would be best for this? Obviously I would have to build it. What would I have to do to "reliably" hold that power from hooning around. What I mean by that, being able to beat on it and possibly once in a while having to repair. Not looking to fix it every weekend/once a month.
 

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My choice would be a NV5600 from Blumenthals and a dual disk South Bend clutch. There customer service is tops in my opinion, just call them and they'll honestly recommend the proper clutch for your HP.
 

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I don’t know there is. Aside from sled pull rigs that have 2 gears, I don’t think I’ve read of a manual that can support that kind of power. That being said, I’m rebuilding my NV4500 with an end state of roughly 650 HP lol. I’m gunna tag along for the ride and see what others say.


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With the available stock manuals for Dodge Ram, the NV5600 is the most stout. However there are other manuals that could be adapted up to the Cummins with the proper adaptor plate. I looked into this to replace my G56, which cost me over 2 grand in direct and indirect costs. The NV5600 didn't get edged out from the increasing HP, in the HP wars, but New Venture Gear went under and Chrysler went with the Mercedez designed G56 for the Brazilian medium duty box trucks. The G56 in the North American market is not ideal for our light duty trucks that want to go 75 MPH and pull 23K GCW. I had to develop a cooling system for my G56 to keep it under 200*, even when at the C&C's 10K GVW. The weak DMF clutch failed at 30K miles, of coarse Dodge wouldn't warranty it due to being a wearable part. So I had the South Bend SMF with the DD 3250 installed. Due to the noise factor I had it inspected by Richard Poels from Standard Transmission and found browned bearings from overheating, further evidence it was running hot. Good luck with your build, you have my attention, and I'll be following this thread.
 

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I know an auto would be all around better at holding power but, I want a manual as this is just a street/show truck.

What I mean by that, being able to beat on it and possibly once in a while having to repair.
What you are looking for can easily be accomplished with a G56. Although the NV5600 is a stout transmission it has never been installed in medium duty trucks and even finding one could prove to be expensive.

Unlike RVTRKN I don't haul 23k at 75 mph and never intend to. Neither will you. My G56 with a SB smf and clutch has given me close to a half million miles only needing one repair. Continuous towing in overdrive kills all the transmissions, the NV4500, the NV5600 and the G56. Standard transmission developed a cooling mod for the NV5600 which is an improvement, but it doesn't make the transmission any stronger.

The G56 comes in two models. The newer one has a taller overdrive and may have slightly different ratios in other gears. The transmissions are easy to find, as are parts. If you were planning on commercial hauling the Eaton would be the best choice, but for street, non-towing the rear tires will break loose before the transmission breaks.
 

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And throwing it in there, you’ll also find threads on Ford’s ZF6. It all sounds like luck of the draw with reliability between the G56 and ZF6. Some swear by the ZF, others the 56. The biggest PITA with the ZF is starter relocation. It goes on the passenger side and can cause issues with your downpipe.


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Unlike RVTRKN I don't haul 23k at 75 mph and never intend to. Neither will you.
This was an example Gary, I never did that towing. As far as the G56 being a medium duty trans? Yes it was, however the rear ratios are a lot higher in those box trucks. To each his own, I know my trans ran hot.
 

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This was an example Gary, I never did that towing. As far as the G56 being a medium duty trans? Yes it was, however the rear ratios are a lot higher in those box trucks. To each his own, I know my trans ran hot.
My point was that towing stresses are a lot different than street driving, even if a person is beating on it. I gave up on trans temp readings with my NV4500. Never once did I get an indication of impending failure with the gauge.
 

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I agree with that, non towing with G56 would be OK. The C&C I used to own weighed in at 10K Empty, I just made it under 10K with no fuel and anything I could remove for Comifornia registration. So normal temps when empty would go over 200*. I could see the temps with the oil flinging in the trans. The passenger side temp was even with drivers side temp, until I was up to highway speed then the drivers side would start to climb in temps and then the passenger side would follow. Towing at 23K GCW it was 5 to 6 degrees higher. That was until I installed my heat exchanger and circulation pump. I would turn it on at 180 and off at 160. After all the money spent replacing DMF, clutch and trans rebuild, (after the inspection where burn’t bearings were found) I spent 3 to 4 grand. It’s why I bought the 2019 HO with the Aisin. Now I have to worry about the CP4.2 🤨
 

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Look up Superstick Transmissions.
You're welcome.
 

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Ok, I looked them up, only wish I saw them a long time ago, but I no longer own my C&C that was hobbled by the G56. However if you want a super-duper heavy duty trans, it wont be the G56. They list there build only to 700 HP where the NV5600 is up to a 1000 HP, and if you want beyond that, no prices advertised, but you can bet it wont be cheap. https://supersticktransmissions.com
 

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RVTRKN,
I wonder if the bearing clearance was set too tight on your transmission? I’ve ran a temp gauge since installation, and I’ve found that ambient temperature has a much greater effect than an empty or full truck. In 90+ weather, mine will run about 156*. This last trip to Alaska with 16880lbs, it did get to 178 on a couple of occasions (90* ambient, hills). I have 1 cooler on the driver side pto (wasn’t room with the exhaust on the passenger side). In some mid 40* temps with rain it would run as cool as 118*. Empty truck (7200lbs) and 100* summer temps would run 163* or so.
 

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I always wondered if it was tight from the factory, that caused the bearings to overheat. But the rebuild was performed by a G56 expert, Richard Poels from Standard transmission. I think the transmission had a slight tweak, the heat was worse with the Mobil Delvac 50 Transmission fluid, to help cushion the NVH with the Solid Mass Flywheel. The thicker the oil, the less heat transfer.
 

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Here's the bearings.
909136
 

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Zf6-750, though I may be a little biased..

Check out the size of the gears in one, beefy compared to any other ld trans ive seen. Large center support and external cooling is icing on the cake.
 

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I also didn’t really notice a difference in running temperatures between the Mobil 50wt and lighter stuff.
I agree with Marco, evidence points to a Ford 6.0 ZF being the beefiest pickup truck transmission. D89 had a post where he talks about the weakness in a G56 being when the gear shafts push apart from each other and the aluminum case flexes enough to let it happen. This of course at power levels way above stock and abusive driving practices. The ZF has a plate in the center of the gear shafts/transmission that prevent the shafts from spreading apart from each other under torque.
I don’t know that the input shaft or gears on a 7.3L ZF would make it any stronger than a G56..... look for the 6.0L one.
 

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I don’t know that the input shaft or gears on a 7.3L ZF would make it any stronger than a G56..... look for the 6.0L one.
The ZF6 was also an option (pretty rare option, but they are out there) for the 08-10 Ford 6.4L trucks as well, so don't limit the search to just the 6.0L years if you're going that route.
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