bullboy85

ok heres the deal, im looking at a 41 jeep flat fender p/u. if i get it i want to put a diesel in it. im thinking a cummins. i want it to be mechanical, so im down to the 12v and the 4bt. now hears the deal im looking to build a best of both worlds setup. so i want it to be fast and i want to gear it to crawl. im thinking the 12v might be to heavy and might have trouble making it fit. i dont think the 4bt is going to put out the hp to make this thing fast though. any ideas? any other options im not thinking of? im attaching pics so u can see what it is and thats a 350 so u get the space im dealing with.

bullboy85

ok that didnt go lets try this

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I SPEED

I was looking to do a 4BT swap in my CJ8, but came across a sweet deal (free) on a complete 4.0 from a YJ, so I'll be doing that instead.

BTW...a friend of mine has a 4BT for sale. PM me for more details.

adidasman23

go with the 4bt. it is a 12v missing 2cyl. i heard you can put 12v injectors in it and all of that. i have a friend that is putting a 4bt in a 80's jeep. its going to turn out nice.

bullboy85

only thing i was worried about there was still getting it to be fast. if u can put 12v injectors in it then i would think u could turn that little thing up pritty good depending on the feul pump... i dont know much about the 4bt eather

wcbcruzer

4BT, that was easy. Depends on what you mean by fast, but I think you can tune them just like our 12v's. Check out:

www.4btswaps.com

All your questions will be answered.

bullboy85

i dont know the more i look the more im not sure, i like the wight size of the 4bt but they seem to say 200 hp max, thast about what i think my jeep wrangler was at with its 4.0 and it was liter, i want it to feel atleast as fast as that. i dont know anyone know of another option?

I SPEED

[QUOTE=bullboy85;2085025]i dont know the more i look the more im not sure, i like the wight size of the 4bt but they seem to say 200 hp max, thast about what i think my jeep wrangler was at with its 4.0 and it was liter, QUOTE]

The stock 4.0HO was rated at 180HP, the 4BT can be built for more than double that. An issue of Diesel Power mag had an old Bronco that had a 4BT with 400HP.

If it wasn't that I got my 4.0 for free, I would be building a 4BT for my Scrambler.

nickg

you cant compare a gassers HP ratings to a diesel, torque is the answer, IIRC whatever the diesel HP rating is add 30% to compare it to a gasser.
in other words
if a diesel engine has 200hp that would be the same as having a 260hp gasser

check the specs for torque on a 4.0 gasser to a 4bt I'll bet that the 4bt has double the torque (and double the fuel mileage & at a fraction of the cost the ability to raise horsepower to twice that of the 4.0)

bullboy85

ya i know that the 4bt has more tq im just looking at that this trucks heavyer, and everything i keep reading says if u want to go over 200 hp get the 12v. i did alot of research and number crunching last night and i think im going with the 4bt. 1 cuz in the cool months when i dont need air it can replace my truck as my dd and i can save alot on diesel. i think i got the setup i want but i dont know, anyone here good with gears and knowing what will work best for milage? if i do the exact same thing as that bronco except with 4.88 id be going 75 at 1700 rpm with both overdrives. now if i go with what i think would be cheaper and get the nv4500 id be at about 68 at the same rpm, plus if i could find one of the old ones with the 6.07:1 first gear i would be going about .8 mpg and 900 rpm in low. i think the nv4500 and the 4.88s is what i would need with the stak tcase that would give me great drivability and milage the 1:1 would be a good setup for playing in the duns and mud the low for rocks, anyone see something i messed up on? thats with 38" tires.

Big Blue24

I would do whatever is cheaper. You will have to twin turbo that 4bt to get the driveability and power you want. The 12 valve could have all the ponies you need with just a stock HX 35.

If I remember correctly, it seems those 4bt motors cost a lot more than 12 valves, but I could be mistaken. As far as gear ratios, 1700 rpm at 68mph will net awesome mileage.

If you get Diesel World magazine, they just did an update about adding a GV overdrive and actually lost mileage at their target 67 mph because they dropped the r's clear down to 1200 in that range. Their opinion was that best engine economy is reached at peak torque. Obviously their Ford motor does not make torque down low like the Cummins so it probably made it even more dramatic.

I wonder how nice it would be to daily drive on 38's? I bet it would not be as fun as you might think, so it might be better to build a truck with less thought on economy and more thought into weekend warrior.

bullboy85

my buddys jeep has 38s and is pritty nice around town, well that and the looks u get are fun too. with the t case in the 1:1 gear and in overdrive the thing would just make 100 mph with the motor at 3200 rpms. in 4th (1:1) i wouldnt quite get to 75 mph. that sounds like a pritty low geared truck to me, id have to be at 2200 rpms in 1:1 in the tcase and to get her up to 70. now whats got me worried is that u think the cost more. i havent reaserched it out, i was going on the understanding that they were cheap and easy to come by..... if thats not the case then i need to keel looking and or see if i can get the 12v in it.

justme-

Don;t forget to upgrade the rest of the drive train to handle the engine- either one has more torque than the factory axles will bare!

Several cj's have been done to 4bt's- lots of help out there for that one.

Depends on speed means to you- if you gear it for rocks and mud you'll suffer at highway and vice versa- pick what you want it to do and build it as such. Remember the best train about diesels is the torque- if you want to go faster just keep adding gears behind it... 6 speed with a GV O/U unit.....but who wants to drive a jeep over 70 mph anyway- it's a life threatening proposition- my CJ sux on the highway.

bullboy85

haha well.... i got pulled over doing 90 in my last jeep. i think i found the 3 speed t case that will let me do it all, it has upgreaded axles, gm 3/4 ton axles, id put a new t case and probibly a nv4500 in it. locker and 4.88s and im thinking the 4bt but afraid it wont get up and go when i mod it like the 12vs do i think i know where to get a 4bt for cheap too. though where im working now i can get a number of different brand small 4 cylender diesels for a good price new but cand find one with the hp and dont know that they can me turned up much...