3.9bt Torq-hp-rpm Chart

[JPETE]

CAN ANYONE OUT THERE IN DIESEL LAND TELL ME WHERE TO GET A TORQ VS HP VS RPM FOR A CUMMINS 3. 9BT 105 HP CPL 858 I NEED TO FIGURE NEW RING AND PINION RATIO --THANKS

 

[Steve Graham]

JPete,

I'm running that engine/cpl in my Scout. You probably know the hp is 105 @2500 and torque is 265 ft lbs @ 1500? I'm using 3. 73:1 gears with the NV4500 5 speed with 33/10:50 BFG MT's. It running 2000 rpm @ 65mph and getting 25 mpg. 28mpg if I drive 60.

The Scout weights 4300 lbs with a full tank of #2.



Steve

 

[driverswanted]

dito on the cpl#858 curve

I'm looking for the same curve information. I want to put my 5th gear rpm at 1600-1700 rpm and road speed at 65. This should be close to the best fuel economy point (basing this on a cpl2303, 110 h. p. curve I have). Then when I tow I just drop to 4th and I can attack hills w/o slowing down because I would be on the forward side of the torque peak. Don't care much about economy for those not so frequent fishing trips when I'm towing 5,000lbs.



Steve's numbers agree with an on-line road speed calculator I use. I plugged in 31. 6" tires, the nv4500 gears , a max rpm of 2500 and his 3. 73 rear end.

I got 1931 rpm @ 65 mph

and 1783 rpm @ 60 mph from the calculator.

His reported fuel consumption agrees with the cpl 2303 curve somewhat. He's still not on the lowest consumption point of the fuel curve, He should get even better mileage if he could drop to 1,600 -1,700 rpm. But that would be less than 55 mph I think.



I'm looking for the Cummins manual part numbers for the 4BT. ready to take my 4BT apart.

 

[Steve Graham]

Jpete,

I have a spread sheet that I use to figure our final drive ratio's, for different tire size's and transmissions and axle ratios. If you'd like a copy let me know.



Steve

 

[driverswanted]

Steve,



Can you explain how you use the final drive ratio? I know you don't want to go too low, because o fgear load factors. but what is too low?



jpete,



Try this location.

http://www.geocities.com/z_design_studio/transmission.html It dosn't give final drive ratios but it does give you your road speed in each gear, giving you the ability to change:

1. governed rpm

2. axle ratio

3. tire number (i. e. size without you having to calulate wheel diameter)

4. transmission gear sizes , with up to 6 gears



It's interactive in that you can move your cursor along either the vertical rpm axis and see the changing road speeds for each gear. Or move your cursor along the horizontal MPH axis and see your RPMs changing for each gear.

Since this is an imperical equation, it does not take into acount for the actual tire size that is slightly smaller than the theoretical size that tire manfacturers give. I tend to fudge this error by subtracting 0. 5" off the calulated tire sizes to come to a more real tire diamter (or radius as the formula converts to). I then pick a tire for my calculation that is 0. 5" smaller than I want to put on the vehicle and use that for the calculations knowing that the tire squashes down about 0. 5".

 

[Steve Graham]

Originally posted by driverswanted

Steve,



Can you explain how you use the final drive ratio? I know you don't want to go too low, because of gear load factors. but what is too low?

I looked at the final drive of my Dodge (mph per 1000 rpm 5th gear) as it came from the factory and what I have now. Factory speed is about 35mph per 1000 and I'm now running about 30 mph per 1000 rpm in 5th(Dodge). I know I needed to fall some where between these two figures and wanted to be closer to the 30 mph than 35. The Scout is setting at 32mph per 1000rpm. Cummins says that for the pre 94 6BTA the power band begins at 2000 and that cruise speed should keep the rpm below that. So I'm asumeing that the 4BT is similar. But right now my EGT's (downstream) are running 600F at 55-65mph and any sign of a hill the EGT goes to 700F-800F. The fueling is stock but I have no idea where the timing is or the condiction of the injectors.

Steve

 

[JPETE]

INSTALLED 2. 71 GEARS ,MILEAGE 32. 02 MPG @ 60 MPH,STILL LOUD LOOKING FOR A NEW QUIET MUFFLER. 1248 MILE CRUSING RANGE ON STD TANKS 18 GAL MAIN, 21 GAL. AUX

 

[driverswanted]

Alright!!!



What muffler and exhaust size did you install? I was thinking of the 3" stainless steel Gibson system made for the Dakota/Durango.



Any words on how you might improve the MPG further?



Dakota 4bt Progress report:

1. Have #858 with SM465 clutch bellhousing. Have adapter information for an NV4500 setup but looking for a 6bt bellhousing already set up with clutch and NV4500 config.

2. replacing H1C turbo with HY35W (9sq. cm. ) for early spoolup.

3. Have two 300-325 sq. in. intercoolers with 2. 5" inlet/outlets. May put both in parallel.

 

[driverswanted]

JPETE,



Interested in how you created your downpipe? I have the same configuration being close to the firewall.



Also interested in how well your insulation is working for sound control an dwould you do anything different to improve sound control.

 

[JPETE]

3.9bt in d150

I insulated the turbo, exhaust manifold, and the down pipe,this is a heat type insulation . I cant tell that it helped the noise at all but it did help the down pipe from heating the firewall ,I will also insulate the muffler and horizontal pipe after I get a quieter muffler. The muffler that is on now came off the frito box van its a straight thru but mounted much farther aft on the van . The drive line came out of ,as did the shifter(cable type) I cut the base down a bit and angled it aft mounted it on top of the original shifter tower it sticks up there but looks ok ,mounted my air horn valve on the aft left side good location for this . I am going to check around for a quiet muffler ,and a cruise control. I will let you all know what I find THANKS FOR THE INTREST GLAD THERE IS MORE OF US OUT THERE . I get lots of looks when they hear that cummins

 

[JPETE]

down pipe

the down pipe was the stock off the box van ,but to long at the first bend radius ,I cut it off close to the turbo coupling flange then cut off as much of the original radius as I could then welded it back together AT 90 DEG