[treetopflyer]

Now that some of you have your 4B's installed, what is it like driving them, specifically engine rpm vs. road speed? I've been reading all I can find and understand that peak trq. is between 1700 & 1900 rpm and red line is 2400-2500 rpm (using stock pump settings and gov springs). I've crunched the numbers on the various gear/xmsn/tire size calculators to achieve "my" best case set up. When traveling at 1900rpm on the hwy do you "feel" like the engine is cruising or being lugged? Does it "feel" like your buzzing the engine at 2200-2400 rpm (wish you could up shift)? I realize people define hwy. speed differently, I'm thinking constant speed of 55-75 mph. I currently drive a VW Tdi but that red lines at 5000+ rpm and is only a 1.9L, so I don't think it's an apples to apples comparison. I'd like some feed back on how you'd gear it for the hwy. if you had the chance to do it again.

 

[Diesel Durango]

no real world experience here, yet. But, according to my data sheet for a CPL 1963 inline pump 4BTA the peaks are as follows:

torque: 1500-1700
HP: 2300 is 131, 2500 is 130, so 2300 is really the peak

for their fuel consumption which is measured in LB/BPH-HR the minimum is at 1700rpms.

I'm no expert, but for this engine, i would guess that the optimal cruising rpm would be 1700rpms for max torque and minimum fuel consumption.

I don't have a data sheet for my cpl 857 which is a 4bta with the VE pump so i can't say how it compares.

 

[scout4bta]

Glad you asked,
On my Scout I choose 33x9.5r15 tyres, 3.73 gears, and with the Nv4500 gives me 35 mph per 1000 rpm in 5th. Which means I duplicated what Dodge did in their trucks for final drive ratio.
75 mph = 2150 rpm, I don't travel that fast for long.
70 mph = 2000 rpm, Setting on the line between economy and power
65 mph = 1864 rpm, Just above peak torque, the sweet spot
60 mph = 1721 rpm, Better mileage
55 mph = 1580 rpm, even better mileage.
(These figures are from my excel spread sheet)
I wouldn't change a thing, for me it's as good as it gets.
My Cummins is a VE pump cpl 858, stock fueling
The only time it's "buzzy" is when I have to drop down to 4th for steep hills and then I let the governer do it's thing.
I use 8 gal to go up to my dad's place in SerriaVista from Mesa and going home I use 6 gal. Google maps says it 192 miles one way, (my odometer says 200), so thats 384 miles using 14 gal= 27.4 mpg. I love it!!

 

[Paul(in NY)]

My Carryall has a CPL 857. I run 60 mph at 1959 R's. NV-4500/NP-205 turing 4.89 Ring and Pinions and 36" tires. Fuel over 3411 miles was 25.9115 mpg. I can run at any legal posted road speed, but I favor 60 in the ole girl.

There are times I wish I had a NV-5600, but for the extra size/weight and cost, i am very happy with the NV4500. I am using the exact same engine/driveline in my M37. Since its a lot lighter, I expect even better economy.

Paul

 

[Av8r]

Maybe not applicable, but:

I have a 6BT in my '94 Dodge. At highway speeds of 75-ish it's turning 2100 rpm at the tach. This rpm does not feel too high. The motor does feel a bit "luggy" below 1500 rpm (but it still pulls like a mule with its tail on fire).

(I'm also a '01 TDi owner, planning on selling it to finance the 4BT project.)

 

[treetopflyer]

That's the kind of response I was looking for...thanks to all. Scout, your set up mirrors what I'm putting in my '69 Bronco with the exception of axle gearing, I'll be running the 3.50's that came with the truck. I want to keep the rev's low because this will be driven many miles to get to where I want to explore, but I don't want it too low that I'm over geared, numerically low, and can't pull weight in 5th.

 

[scout4bta]

With 3.50s (3.54?) a 235/85r16 tyre would much match my setup, assumeing you have a NV4500.

 

[treetopflyer]

Scout, I'm looking at Dick Cepec metric equivalent of 33x12.5/17's on a steel rock crawler rim. Aluminum wheels look nice but can't be "field" repaired if you bash one on a rock.

 

[scout4bta]

That should work. Looks like you'll drop about 100 rpm for each gear from what I posted for my Scout. I'm using a BFG Mud 33x12.50r16 as a example for the size as they provide the revs per mile for a accurate caculation. I also used a 3.54 ratio, if it is a 3.5 then you'd drop about 150 rpm for each gear.
BFG 33x12.5r16= 630 revs per mile=32.01 dia

75mph 2011 2034 2144
70mph 1877 1899 2001
65mph 1743 1763 1858
60mph 1609 1628 1715
55mph 1475 1492 1572
===================
gears-- 3.50 3.54 3.73