4BT VS a carbed 318

[Lonesome7.3]

I am just kicking this idea around here so do not pass judgment too quickly. I have a 1972 Dodge D200 with a 318 and 727 that I am pretty much stuck with. (It has been in the family since it was new.) Do not get me wrong, I do love that old truck. But an all original 3/4 ton gasser does wear on my patience quite a bit. I would love for the truck to appear original outwardly, but have more modern and reliable stuff underneath. I can repair a diesel engine a lot better than I can this old gasser. So the way I see it, this old and reliable stock 2BBL 318 most likely puts out the same if not less power than a stock Cummins 4BT. So I figured with a few mild mods and a good overdrive transmission a 4BT would do this old truck nicely and get me down the road with fewer 30 something year old issues to correct every week. Feel free to chime in. What would the pro’s and con’s be on swapping out that old low mileage 318 for a 4BT?

[Lonesome7.3]

By the way, I already have an early 90’s Dodge donor truck with a Cummins 6BT in it. The 6BT is slated for another project. But everything else from the truck can be used to support a 4BT swap into the old D200.

[raunch]

You might have to do a body lift to fit the 4bt under the hood.

[Lonesome7.3]

Really? I do nto see much difference between the 72 gasser and the 90 something with a Cummins.

[NH2112]

I'd probably consider something like a Howell EFI setup, MSD ignition, and maybe a cam to wake the old 318 up a bit, assuming it's in good enough shape to benefit from the mods.

IIRC in 72 the 2bbl 318 was rated close to 200HP, my 76 & 77 were both around 160 and that was after they changed the way in which HP was measured. Most 4BTs from bread trucks, gensets, and other industrial applications were good for about 110HP, if it has the inline Bosch pump anything that increases power in a 6BT will work for the 4. If it has the rotary Bosch pump I'm not sure what works for performance upgrades. AFAIK the inline pumps are good for up to about 250HP and 400lb-ft. A friend put one in an 84 C2500 several years back, installed an Allison from a wrecked DMax and standalone computer, and went with the tallest gears available (3.30ish, I think) and was getting over 30mpg average.

[Lonesome7.3]

My plan right now is to upgrade the old 318 a bit when I rebiuld it. But I would like to consider the possibility of converting it first. I prefer having an oil buner under the hood.

Your friend's biuld sounds interesting and costly. The Allison had to be a ton of money. What kind of highway speeds does he reach at what RPM? That is my biggest concern. I want to travel down the highway at a reasonable RPM and with a four cylinder pulling a trailer I have some concerns.

[Edahall]

From what I've read, those who have done the 4BT conversion wished they had just gone ahead and went with the 6BT when all was said and done. The major complaint with the 4BT is major vibration especially at idle and noise. Being that it's a 4 cylinder, it's unbalanced while the 6 cylinder is balanced so it runs a lot smoother. Both engines get good gas mileage. My Cummins Suburban gets 26 mpg on the freeway and I have it geared such that it turns just a tad bit over 1300 rpms at 65 mph. These engines like to cruise at RPM's under 1800 rpm's. If you're going with an OD transmission, you want 3.43 or 3.54 gears and without OD, you want either 3.08 or 2.73 gears.

The 4BT or 6BT should be able to be shoe horned in there without any body lift. My 1990 Suburban didn't need any body lift even with the huge 6 speed NV5600 transmission behind the Cummins.

The 4BT can make major power even if it has the rotary pump. The rotary pump is easy to turn up. On a 6BT, the rotaty pump is good for 500-600 hp while the P pump is good for over 1000 hp.

Is the 1972 Dodge 2 wheel drive and 3/4 ton?

[Lonesome7.3]

I was planning on keeping the 4:10 gears I have now in the D60. With an over driver would that not be enough? I have considered dropping that 6BT in there but for some reason the 6BT seems like a better way to go. At least in my mind.

[Edahall]

With 4:10's even with OD, you'll be severely limited on speed with the Cummins. Both engines (4bt and 6bt) are longer stroke (4.21 in) than the other competing diesels so they run better at lower rpm's. As I mentioned earlier, I have mine geared to run at 1300 rpm's at 65 and it does fine and gets good gas mileage.

[Lonesome7.3]

I am glad you brought that up. I was under th eimpression you want lower gears with a smaller displacement engine.

[Edahall]

Here's the power curve for a 4BT in stock form.
105 horsepower @ 2500 rpm, which is redline
265 torque @ 1700 rpm

http://i256.photobucket.com/albums/hh194/tehintranets/Diesel%20YJ/torquecurve3.png

[93GMCSierra]

I am glad you brought that up. I was under th eimpression you want lower gears with a smaller displacement engine.

That depends on the redline, and the torque, diesels having way more torque then gassers means they still take off from a standstill with higher gears even with less HP

[NH2112]

The major complaint with the 4BT is major vibration especially at idle and noise. Being that it's a 4 cylinder, it's unbalanced while the 6 cylinder is balanced so it runs a lot smoother.

The 4BT needs to idle around 1000rpm to eliminate the vibration. The noise is going to be there regardless.

[Lonesome7.3]

The Isuzu engine almost looks like a better choice. Thos numbers help, thanks. That give me an idea as to what I will be getting. I really have to find out what the 318 is putting out so I can compare them.

I figured the noise is just a part of owner a smoker. I plan to insulate the cab anyway.

[NH2112]

A mid-70s 2bbl 318 was about 165hp@3600 and 255lb-ft@1600. An earlier model probably was rated for quite a bit more before the method of measuring power was changed in response to Congress basically banning muscle car production.

[Lonesome7.3]

Funy how thst sort of thing works out. So it looks as though the nymbers I had in mind for both engines are pretty close.