Which engone swap to do??

Ya I already have a GM goodwrench 454 crate. With the turbo 400 and the 4:11 or 4:56 gears (I can't remember exactly what they are) I'm only getting about 5-8 MPG. There has to be something wrong with my emissions or something else I'm told. Even if it were running great I figure about 10 is about all I'll get out of it. That's the main reason I want to go away from the gas engines. If I can run a diesel and get 15-20MPG it won't take long to pay off a diesel swap and start gaining money over the gas engine. I figure at about 15k miles just in fuel cost I should have the swap paid for.

What is the 4BT found in?? Whats the difference in the 4BT and 6BT?? I've seen swaps done on the 6BT but I don't think I've ever heard of the 4BT.

4bt is a 4cylinder cummins.

6bt is a 6 cylinder cummins

you can find 4bt's in those old frito lay trucks.

Thanks for the info Sparky. After hearing the answer it made me want to smack my self in the head it was so obvious lol. Well you were also right about the 4BT being expensive.
The good news is that in my area after a quick glance on Craigslist, I can get an entire 2wd dodge 6BT with less than 200k miles in good running shape for about 3500 bucks. That should give me most of the parts to do a 6BT swap and have a 454 crate motor and lots of parts left over to sell and recoop some of the upfront cost.

If I go that route I guess I'll have to figure something out with my hood clearance. I'm not a huge of any hood other than the stock one, but for a Cummins I think I can look past a terrible hood.

Should i run the dodge trans or sink the cash into the adapter to run a chevy trans?? I've heard a lot of terrible things about dodge trans but wouldn't it be easier, cheaper, and better for the highway with the dodge trans?

The lack of overdrive is what is killing your mpg.

Run the dodge trans.....mines shifts great and has overdrive....and my truck has 3.42 rear....and ive been driving it everywhere since tuesday and the fuel gauge just started moving....anybody know how many gallons a 3500 fuel tank is on a 91 model (box style)?

What I've been told about the Dodge automatic is that lots of idling kills them because the fluid doesn't circulate through the cooler while you're in Park. And you know a lot of diesel guys idle their trucks constantly...especially those doing transport work or similar. Trans builder buddy of mine suggests if you're gonna idle it much, set the park brake and shift into neutral.

Richard

Most Dodge automatics will not stay together for long periods of time behind a cummins... especially if you go with an OD auto... the TF727 would stay together but thats the last good auto Dodge built... If your swapping and are getting a complete donor truck, spend the time and find one with a manual.. chevy and Dodge used the same 5spd trans just different bellhousings.. it would be an NV4500... or a 6spd.. if you got lucky.. that would be the NV5600... But a 12 valve with a manual would give you really good mileage, and damn near unlimited pulling power... and its the cheapest diesel to repair.. and parts are very plentiful.

can you adapt it to the TH400?

I have to ask. Are you going to do alot of hauling with this truck? Even if you are how heavy? With the torque of the big block i dont see the need for a 4:11 or even more so a 4:56 gear. An OD tranny swap or 3:73 3:56 gear sounds way easier and cheaper

Even with some highway gears the mileage still sucks. My 454 is a dog, hp and torgue numbers are embarrising for what it is. I have an article from mag that they did a gear swap in my exact truck and only gained like a mile per gallon or so. My wifes old audi wagon had a v6 twin turbo with more hp and torque than my truck. Just plain sickening. I can get twice the mileage of my dually with my duramax 4wd plus be able to hammer down at 70mph with 10000lbs behind me and pass people. I cant do that empty in my dually.

Once you go diesel, you dont look back.