C. Garbee?

Josh · Post by **Josh** » Fri Feb 08, 2008 6:14 pm

Cabel,

I sent you a PM but didnt get a response...

does anyone here know what he gets for fuel economy with his 4BT and 5 speed, and what his 60 MPH cruise RPM is?

Lifer · Post by **Lifer** » Fri Feb 08, 2008 7:42 pm

I'm not sure what his mpg figures are, but I can guarantee he gets better gas mileage than he did with the original engine. That 5-speed probably dropped his rpm pretty significantly, too. I'm sure he'll exercise his bragging rights and let us know as soon as he sees this thread.

Josh · Post by **Josh** » Fri Feb 08, 2008 8:48 pm

Im hoping when I 4BT and NV4500, with my dana 60 4:10's and some 40" rubber I can get that cruise RPM down to around 1500 or so RPM, and still maintain a 60:1 low range crawl ratio.

My Audi only gets around 26 MPG average (330 HP twin turbo V6 driving all 4 wheels, hard to keep my right foot off the floor

) so if I could squeak 24 or so out of the truck, I'd drive that just about as much as the Audi.

Lifer · Post by **Lifer** » Fri Feb 08, 2008 9:00 pm

Age cured my leadfootitis a long time ago. LOL My Dodge Dakota with its 318 cid V8 gets about 26 mpg, and my wife's Chrysler T&C van gets about 34 mpg while staying within the speed limit. I'm satisfied with that. My '55 Pontiac (397 cid) gets about 10 mpg and my '79 Cadillac limo (472 cid) gets about 12 mpg on the highway as long as I keep it down to about 50 mph. Open it up a little, though, and the speedometer and fuel guage needles go in opposite directions at about the same rate. The Pontiac is sold and awaiting pickup, but the Caddy is available. You want it?

Josh · Post by **Josh** » Fri Feb 08, 2008 9:49 pm

Im afraid Im going to have to pass on the caddy. Two money pits is quite enough!

I got a NOS set of drag links for the elder money pit for $20 shipped on eBay. Showed up yesterday, they look nice.

On a side note, the twin turbo terror:

I love it, its quiet, comfortable, and retarded fast. The best part is being silver and having 4 doors, its invisible to cops.

MSeriesRebuild · Post by **MSeriesRebuild** » Sat Feb 09, 2008 8:10 am

Josh wrote:Cabel,

I sent you a PM but didnt get a response...

does anyone here know what he gets for fuel economy with his 4BT and 5 speed, and what his 60 MPH cruise RPM is?

Cabell's MPG is over 20 I believe, I've heard him say, but don't remember the exact figure. We have done many Cummins repowers, the peak torque range for a 4BTA is at 1600 RPM. I wouldn't want my cruise below that RPM for 1 simple reason. When you romp on the accelerator in high gear at under 1600 RPM, there would be a slight hesitation until you achieved 1600. If you romp down at 1600, it's like someone pulled in behind you a gave you a push. The Cummins is a real performer in the 1600 - 1900 range.

CGarbee · Post by **CGarbee** » Sun Feb 10, 2008 6:49 am

Never got your PM… Wonder what happened…?

Anyway, to answer the question in a long winded manner:

I went on a round trip to Aberdeen, MD, with the East Coast Convoy in May 2007, in my M37 with the Cummins 4BT, ZFs5-42 (0.76:1 fifth gear), 4.89 gears. Hardtop, bows mounted over cargo area, but canvas not mounted. 900r16 Michelin XZL tires (35" diameter). Max speed for trip about 55mph, had to keep it down due to trailing M35A2C for entire trip (mine, driven by my buddy Chuck) and due to the rest of the guys in the Convoy having similar pace vehicles so average was around 50mph (what I tried to hold it at)... Only had a M37 cab, a winch, and fourteen one gallon cans of string beans and potatoes in the bed for the ride up, ride back I had a M37 hardtop and a generator.

It was a 758 mile roundtrip. I burned 30 gallons of fuel... works out to 25mpg...
My "normal' leadfooted driving habits around town and on the highway yield an average of 17mpg, but I routinely am running at 75mph down the Interstate to work and/or doing the stoplight dragraces downtown... Full throttle is not the way to economy.

Keep in mind that I have turned a wrench on every single bolt and fitting on my truck, I have gone through things like steering and brakes, etc. I have seatbelts, and electric wipers, and H2 E-code headlights, and four wheel disc brakes with a dual circuit master cylinder, and new brake lines, and new wiring harness, and LED full red lens (M561) taillights, and turn signals, etc... I go under and over it on a weekly basis. In short, I know my rig, it's well maintained, etc. I also pay attention to what's around me as I drive, and adjust for road conditions (including MY condition, and that of folks and the environment around me...). Hence, I feel good about taking it on both long and short trips, at speed… I feel equally good about taking it offroad.

I have a page on my website with useful equations (such as the one used to figure MPH for a given engine/overdrive/transmission/transfer case/rear end/tire combination…
See:
http://www.garbee.net/~cabell/equations.htm

You can use the equations (helpful if you plug them into a spreadsheet or scientific calculator) to figure tire/gear/rpm changes forwards and backwards before you start ordering parts…

I turn 2100 rpm’s at 60mph… 2600 rpm gives me 75mph (and I am right up on the governor stop, hence, the poor economy when I wind it up like this…). The 55mph for the Aberdeen trip last year was done at 1900rpm with 50mph occurring at 1750rpm.

I sometimes think that it would be nice to mount some taller tires (there are some Michelin 1100r16’s mounted to a truck in the backyard), but I like the way my truck looks and drives as it is, especially when I am idling over stuff offroad, or pulling a fully loaded M101A1 when the truck is also fully loaded, up hills…

Josh · Post by **Josh** » Sun Feb 10, 2008 4:32 pm

Im assuming that you guys are running stock 120HP 4Bt's?

I was going to do a turbo swap, aftercool it, and bump the pump a bit to get it up to around 160 or so. The guys over on a few 4BT repower forums say that the peak efficiency actually occurs if you change to a larger turbo and play with the injector pump a bit.

The NV4500 has a .75 OD, times my 4.1:1, will yeild a final drive of 3.07:1.

With a 40" tire, Id turn 1560 @ 60 MPH.

a 38" tire would give me 1650 @60 MPH.

And my stock 34" would give me 1825 @ 60 MPH.

I'd really like to run 40" tires, (goodyear MT/R) and I had planned on turning the front springs around to lengthen the wheelbase 2" (they are 22" from the rear shackle to the centerline, and 24" in the front). This 2" bump would give me all I need to fit 40" without any suspension lift. All I would have to do is cut and shorten the drag link from the axle to the pivot pin.

CGarbee · Post by **CGarbee** » Mon Feb 11, 2008 6:50 am

Actually, my personal truck is powered by a 1990 ReCon Cummins 4BT rated at 105hp with stock pump, injectors, and turbo...

I believe that a NV4500 has a fifth gear ratio of 0.73:1 (not that there is a heck of a lot of difference between 0.75:1 and 0.73:1...). My ZF S5-42 has almost the same ratios throughout the box as the ZF with an OD fifth of 0.76:1... It's a good match for my rig.

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