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4bt to 6r80 trans

7841 Views 35 Replies 11 Participants Last post by  Redark1, 
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I've decided to go another route on my 07 expedition. I've been rolling with a m5r2 trans for the last 5 years and 35k miles and something in the clutch system is not good. I also haven't been able to get 4x4, or cruise control working. So its time to change it up. I'm going with a 6r80 trans which is quite proven in the gasser world. So I have a few questions, I doubt the trans has been put behind a 4bt yet. Ill be machining the adapter plate myself. My current power is probably 225hp...assuming 450tq. The trans is easily rated for this from the 5.4.

Should I use a stock converter to get a baseline for how it will run? Will a stock HD flexplate be good for this application? Will a 5.4 starter start a 4bt?

Trans will be tuned with hp tuner.

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Ok. Thanks guys. I'll be sure to get a proper stall speed on whatever converter I go with. Ill be calling destroked tomorrow to see if they have an adapter plate for this, I prefer to machine my own parts, so if I buy my own adapter it'll feel like sacrilege.....but time is important for this build. Did some research, and it looks like the target stall for the 4bt is approximately 1400-1600 ish rpm?

Detroked flex plates are really expensive, this I think ill make myself.

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Just spoke with destroked and the woman I talked to claimed they don't make an adapter for the 6r80, but not going to lie she didn't sound very educated on transmission adaptes when that is what they speciality in.

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Talked to my converter builder tonight and he think he can build what I need for pretty reasonable. After that I can take a good look at the adapter thickness. Still not set on what flex plate as that kinda converter dependent. And the starter is kinda flex plate dependent.

Anyone know a common power rating on a 4bt starter? Would love to use a more compact starter cause space is so tight. I found that a typical 5.4 starter is about 160ft/lb tq.

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Project update:

Much time was spent on what combination of parts to go with. Ideally I wanted to start with a dodge/cummins flexplate, as that would bolt to the crank. But due to the large diameter of the dodge flexplate it wouldn't work with the smaller size of the bell housing on the 6r. So after eyeing some dimensions of other parts, ive opted to start with a 6.0 powerstroke flexplate and starter. The 6.0 flex plate just barely fits in the 6r bellhousing....not that that really matters. So I machined out the center section of the 6.0 flexplate and machined a new center section with the cummins crank bolt pattern. Since starting with the 6.0 flexplate, ill also be using the 6.0 base torque converter, as that will mate to that flexplate. Using the 6.0 flexplate will put that starter snuggly against the block.

Since I'm going with essentially a 6.0 converter it will actually stick out of the 6r bell housing because of the size of it. The 6.0 converter will of course get all the proper guts to make it mate to the 6r. My converter guy will hopefully have the converter done next week. So unfortunately because of the converter stick out, my trans to engine adapter will have to be about 3" thick. After I get the converter and everything this week I'll order my block of aluminum to machine the adapter.


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Alas, no. Hope that's not what I implied. My converter guy is starting with the piece of the 6.0 converter that mates to the 6.0 flexplate.....i believe this will be a forged aftermarket piece. From this he will build it with the proper mating guts that will joint to the 6r. Sorry I'm not up to speed on my converter lingo.

Does that clear it up?

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Vern said:
Are you having a trans built? If so, what mods have been recommended?

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No, im going with a stock trans. I did contemplate a billet input shaft. This trans is rated at i think 490lb torque, and my setup should be right on the brink of that. Nothing ventured, nothing gained.

I plan on using hp tuners to tune the shifting of the 6r.

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Finally got my converter done. As I said its based on a 6.0 powerstroke converter with off the shelf guts from sonnax to have all the trans input shafts to mate with the 6r trans. Guy said it should be good for more power than what I'm making. Looking forward to getting my metal bought for the engine to trans adapter. I think the thinnest plate i can start with is 2.5" thick. Hoping to order my metal early next week and start maching next saturday. Here's some pics of the converter.


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Snuggletough said:
That is a seriously strange way of doing what you want.

That flexplate center thing you machined looks iffy. What is up with the big oops groove cut into the face? Are you a machinist or a hobby guy with a lathe and a mill?

When flexplates fail it's usually in the high stress area right where you put your weld. Welds done by hand are a bit iffy for stuff like this. Flexplates are rather intolerant of thickness changes like that. By design, it flexes, and flexes differently depending on load and line pressure (converter is basically a metal balloon).

Hope it works, but you have gone down a misguided rabbit hole IMO.
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Show me this "oops" you are referring to? For some reason I can't see it in real life or the pics.

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After considerable time, I finally have the adapter machined out. Not all areas were finished with a finish mill, just left a roughing mill finish. Started out as a 100lb hunk of AL, yeah that was pricy. I'm happy with how it turned out. Still need to do a couple small things to finish it up. I utilized a 6.0psd starter and it sure is snug to the block.


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char1355 said:
That a very serious looking adapter you made. Nice workmanship. See you have twin turbos. If you're only putting out 225 HP you must have the fuel turned down or are using stock injectors. With a set of 5x.012 injectors that can easily do 300 HP even with a VE injection pump. With a P pump it could go much higher.
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It's your typical hx30 over hx35 setup, running 5x12 injectors with VE pump. Fuel screw isn't quite maxed out. Maybe my hp guess is low? I dont know. I expect the vehicle to feel quicker after the trans swap.

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Chopped105 said:
Love your work! Currently designing an adapter which I will end up milling much the same as you did, except for a 6l80e instead. The flex plate looks awesome, I'm want to do something very similar to that too.
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It's been a long haul for sure. I really feel the flexplate will hold up fine. Currently having the block checked out by a shop for cracks. After that is on to final assembly of all parts. Just be careful to get all centerlines of the trans and engine on the same line.

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It's been a long haul on this project. Engine still on the stand. I've never been satisfied with my turbo drains on my compound setup, and that's my biggest roadblock right now. Seems simple I know, but I'm going to make sure they never leak again.

I'm predicting good things from this trans. .....I just have a hunch I'm going to be really happy with it.

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Sorry I've been gone a while.....so long I can't even reply to my PM's....(sorry reddark1).

It's together....running, but not moving. Hitting some road blocks.

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