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I'm looking into doing a 4bt into a suburban. The sub I'm looking at has a th400 in it. I didn't catch the diff tags but I'm sure it has either 3.08 or 3.54 gears. Tire size will be in the 35" range. This puts it at 1900 rpms at 65 mph and 2200 rpms at 75 mph. This seems like a decent cruise rpm for the 4bt but do you think it will be a dog off the line or around town? MPG's are a concern but I don't want to be getting 28MPG on the highway in that configuration only to be chugging around town or on every steep grade.

I'm sure the overdrive trannies (700r4, nv4500, 4l80) can be put in but I think that would pretty much kill the old budget.
 

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I'm running that setup

3.50 gears, 35" tire. Plenty power off line in early bronco. Tops out just above 75MPH.

Lot more usable power vs gasser.

Have mine set up for 40-65 top gear. Shifts in and will hold low thirties, but down shift with throttle, below 35.

Bigger vehicle may get better mileage than mine, since I do not load the turbo much.
Wayne
 

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Discussion Starter #3
I'm used to driving a 4cylinder toyota on 37's so it doesn't move unless the engine is in its sweet spot

I'm not too familiar with gear setups on a diesel powered rig. So I take it that using a th400 won't kill gas mileage if I go taller on the gear ratio/tire size because the diesel can pull that easy. I know that if you did that to a gas engine, it would just lug itself and suck fuel.
 

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Just think about all the Gm trucks with the Th400 ,with the right gears and tires it will do just fine !

The Cummins is like no gaser .

CrewCab59
 

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my chevy with 35s

Iam running a 4bta in my 85 chevy with 35s a turbo 400 and 3.73 gears, the truck has more than enough power, the back brakes were not bled out good and it is turned up, it will go through first and second gear if you power brake it. Ithink 3.08 would be great, I changed governor spring just so I could go 70. I think you will be fine.
 

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Ain't no one mentioned it yet but if the Burb is a gas burner then you'll be spending moe money on a new T/C and Valve body rebuild (Spring's & such)
 

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Discussion Starter #7
its a gas 5.7

I know it will need a much lower stall TC and a modified governor

What else will the valve body need as far as "springs"?

jessejonassen: what do you typically get for fuel economy and how is passing power on the highway with that setup?
 

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mileage

I curruently get about 18 mpg but I also drive it hard. It has plenty of passing power with the 3200 governer spring, with the stock spring id you wanted to pass someone going 65 it was allready defueling at aout 2200 and it wouldnt pull hard, change the sping its worth it, although it may be better with 3.08 gears because at the same speed you wouldnt be close to the defueling point of 2200.
 

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Use existing TH400

I have a 91 fullsize Jimmy. It has a knocking 6.2 and 700R4/241 and 3.08's and 31's. I have my Fritolay trick with a 4BTA and TH400.

Based on getting the simplest swap done (I need a new daily driver), do you think that using the TH400 instead of hooking up the 700R4 at this point is decent as a daily driver? The TH400 in the Fritolay truck has a cracked bellhousing, but it could be welded up I think. Then I just need a 4x4 TH400 for a donor output shaft (and possibly a case) and the adapter to a 241.

This seems like a faster swap than getting the existing 700R4 hooked up. The truck has 195K miles, so I have no idea what state the 700R4 is in anyway. I'm in Colorado, but I'm not usually driving 75mph on the highway. Commuting is 55-65.

Any input would be great.
 
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