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Discussion Starter #1
I am building a '85 Suburban K20. I was planning on building it around a 454 but didn't realize how easy it would be to get a Cummins in. After reading here I am considering the swap.

What I have is a '85 K20 Burb with a carbed 454, 4l80e (Compu-Shift controlled), Np205 transfer case, Dana 60 front and 14bFF rear, 4:10 gears, 33 inch tires and 4 wheel disc brakes.

Should I go 6bt or 4bt? I was thinking 4bt for the economy but 6bt sure would be fun. I would probably buy the PATC trans adapter to keep the engine vertical, would it still fit under the hood?
 

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I am building a '85 Suburban K20. I was planning on building it around a 454 but didn't realize how easy it would be to get a Cummins in. After reading here I am considering the swap.

What I have is a '85 K20 Burb with a carbed 454, 4l80e (Compu-Shift controlled), Np205 transfer case, Dana 60 front and 14bFF rear, 4:10 gears, 33 inch tires and 4 wheel disc brakes.

Should I go 6bt or 4bt? I was thinking 4bt for the economy but 6bt sure would be fun. I would probably buy the PATC trans adapter to keep the engine vertical, would it still fit under the hood?
If you're going to do any towing, I'd recommend the 6, otherwise the 4 "should" be adequate, but maybe not as fast as you'd like. Go with the chevy adapter, keep your setup - the tilt is no problem to deal with. I believe CrewCab has pre-fabbed motor mounts for your application - check out the vendor's section.

I had an 87 burb with a 454 FI and a 4speed. 8-10mpg. :(
 

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I am building a '85 Suburban K20. I was planning on building it around a 454 but didn't realize how easy it would be to get a Cummins in. After reading here I am considering the swap.

What I have is a '85 K20 Burb with a carbed 454, 4l80e (Compu-Shift controlled), Np205 transfer case, Dana 60 front and 14bFF rear, 4:10 gears, 33 inch tires and 4 wheel disc brakes.

Should I go 6bt or 4bt? I was thinking 4bt for the economy but 6bt sure would be fun. I would probably buy the PATC trans adapter to keep the engine vertical, would it still fit under the hood?

I put a 6BT in a 1987 Suburban. I used a Dodge adapter, flywheel, clutch, and bellhousing. I put a Dodge input in my Chevy NV4500, and used the Chevy transfer case. Used a Ford 7.3 PS intercooler in front of the AC condensor. Had to modify the hood safety latch though, but it fit well. Also had to do a 2" body lift. Fit pretty well, but if I had to do it again, I would use a 4BT, simply because of the weight. A mildly bombed 4BT is more than enough for a Suburban.:grinpimp: I would suggest going with 3.73 gears though. They are the tallest gears that you can get for a 14Bolt, and a Dana 60, that will match.
 

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Discussion Starter #5
Thanks for the input.

The RPM output and TPS shouldn't be a problem.

With my current setup I am getting 11 mpg. I can sell the 454 for what a used 6bt will cost. As for savings it probably will not save me a thing as gas is $2.60 a gallon and last night diesel was $3.07. The coolness factor would be great though.

Thanks again.
Ron
 

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The straight axle trucks doesn't need a body lift for the Conversion.

The intercooler
1st gen dodge works great 81-87 C / K trucks.
2nd gen dodge works 88-91 R / V series trucks.


The mounts has a lot to do with fitment ,the 6b will clear the hood.

The question 4b or 6b ,the 6b would work better do to the weight of the burb ,a 4b would need turned up .

Choice is yours .

Scott
 

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Thanks for the input.

The RPM output and TPS shouldn't be a problem.

With my current setup I am getting 11 mpg. I can sell the 454 for what a used 6bt will cost. As for savings it probably will not save me a thing as gas is $2.60 a gallon and last night diesel was $3.07. The coolness factor would be great though.

Thanks again.
Ron
if you figure your 11 mpg @ 2.60/gal vs. 18/19mpg @ 3.07/gal you will be saving money!
 

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Discussion Starter #9
mcinfantry, you are correct, Compushift does not NEED RPM input but for complete functionality it does, but should be pretty easy to do.

bigorangecntry07, I have owned a '94 Dodge Cummins 4x4 SC 1 ton and a '03 Dodge Cummins SRW CC. Both, with my driving style got lows of 15 empty and highs of 18 (only a couple times). I'd still probably save some but based more on longevity.
 

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mcinfantry, you are correct, Compushift does not NEED RPM input but for complete functionality it does, but should be pretty easy to do.

bigorangecntry07, I have owned a '94 Dodge Cummins 4x4 SC 1 ton and a '03 Dodge Cummins SRW CC. Both, with my driving style got lows of 15 empty and highs of 18 (only a couple times). I'd still probably save some but based more on longevity.
im adding it to mine. inly cause im curious. what functionality am i loosing by not having it? the compushift is measuring input and output rpm at the tranny anyway.....
 

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I never see you mention, but when I did mine I had to cut the center crossmember and lower it 3" and the front one had to be notched a good bit to clear. With out that mod. the engine was severely tilted up in the front and front valve cover looked like it would hit the hood. Is the 91 different in the cross member area?

Also, if you cut the bottom 4 tubes off of a 2nd gen. coole and notch the original snorkle holes in the core support it makes a very nice installation. You have to cap the tanks and weld some mounts on, but I personally like the way it fits with the tubes up high.

The straight axle trucks doesn't need a body lift for the Conversion.

The intercooler
1st gen dodge works great 81-87 C / K trucks.
2nd gen dodge works 88-91 R / V series trucks.


The mounts has a lot to do with fitment ,the 6b will clear the hood.

The question 4b or 6b ,the 6b would work better do to the weight of the burb ,a 4b would need turned up .

Choice is yours .

Scott
 

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Discussion Starter #13
im adding it to mine. inly cause im curious. what functionality am i loosing by not having it? the compushift is measuring input and output rpm at the tranny anyway.....
Several things. With the TPS and RPM the Compu-shift calculates engine load, not just using the TPS and ourput shaft. The output shaft is used more for the speed of the vehicle.

Also, there is a feature of the compushift which is called "Always up-shift". You can set this to any RPM you want and when the engine hits that, no matter what anything else is telling the controller to do, it upshifts based on that RPM. Makes it nice for different engines.
 
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