6bt cummins NV4500 1996 LX450 swap

[zhonghuihe]

That’s a great question. Those calculations are very close to where I’m at. I don’t think the tach on my dash is 100% accurate. I’m feeding the tach with a Dakota digital box that’s measuring rpm’s on my alternator. I had to calibrate the Dakota digital box. To do this, I used a harbor freight rpm meter to measure rpm’s on the crankshaft pulley. This may be causing an inaccurate reading within the calibration.

Also, those online calculators are a mathematical formula and can’t always account for variations in driving conditions and engine efficiency. I’ve had mechanics tell me the online calculators give a good ballpark range.

65mph is where I am seeing the sweet spot in terms of fuel efficiency and rpm’s. I am getting around 20 mpg when I keep it at 65mph and control my shifting.

The online calculator is just a mathematical equation, and it is accurate in my experience. In manual trans, tire size, 5th gear ratio, final drive ratio, and in your case the 10% OD in your transfer case are all fixed factors, there is not much variable factors in this case, so the calculation should be fairly accurate.
my previous screen shot did not take into consideration of your 10% OD, if I do, then it would make your final drive around 3.2.

You should be no where near 2k rpms if you are doing 70.

I learned a lot reading your threads and planning on getting the 10% OD and 3.55 gears myself after reading your posts. that's why when you mentioned the rpms at higher speed, something does not line up to me there.

 

[Major Tom]

The online calculator is just a mathematical equation, and it is accurate in my experience. In manual trans, tire size, 5th gear ratio, final drive ratio, and in your case the 10% OD in your transfer case are all fixed factors, there is not much variable factors in this case, so the calculation should be fairly accurate.
my previous screen shot did not take into consideration of your 10% OD, if I do, then it would make your final drive around 3.2.
View attachment 3896500
You should be no where near 2k rpms if you are doing 70.

I learned a lot reading your threads and planning on getting the 10% OD and 3.55 gears myself after reading your posts. that's why when you mentioned the rpms at higher speed, something does not line up to me there.

Here’s a photo of my mph and rpm’s. I know the mph is right because I used my garmin to measure and calibrate the lutz box.

The tach may be where the data is inaccurate.

 

[NeverFinis]

First great work on the swap.

My 2 cents.

Those rpm calculators are spot on.

Driving conditions do not matter. Engine efficiency doesn't matter.

At highway speeds, automatic vs manual doesn't matter. Automatic will have its torque converter locked up at highway speeds.

Tire size isn't always accurate. Sometimes I use revolutions/mile instead, if the number is provided by the tire manufacturer.

I have a L96/6L90e with 4.10s and 35" tires (BFG AT KO3) and I am spot on at 2000 RPM at 70MPH. Final gear of a 6l90e is 0.69. I can read the RPM from the ECM, which is how I adjusted the Toyota tach. Can't do that with a cummins though...

No Dakota Box needed for the tach, if the engine has a tach signal, as the Toyota tach can be adjusted for different engine frequency pulses.

 

[Major Tom]

First great work on the swap.

My 2 cents.

Those rpm calculators are spot on.

Driving conditions do not matter. Engine efficiency doesn't matter.

At highway speeds, automatic vs manual doesn't matter. Automatic will have its torque converter locked up at highway speeds.

Tire size isn't always accurate. Sometimes I use revolutions/mile instead, if the number is provided by the tire manufacturer.

I have a L96/6L90e with 4.10s and 35" tires (BFG AT KO3) and I am spot on at 2000 RPM at 70MPH. Final gear of a 6l90e is 0.69. I can read the RPM from the ECM, which is how I adjusted the Toyota tach. Can't do that with a cummins though...

No Dakota Box needed for the tach, if the engine has a tach signal, as the Toyota tach can be adjusted for different engine frequency pulses.

Thank you for the information on the Toyota tach. Friend, I’m happy to agree to disagree on the accuracy of the online calculator. Do you have information or links on the Toyota tach and how it can be adjusted for different engine frequency pulses.

 

[NeverFinis]

Thank you for the information on the Toyota tach. Friend, I’m happy to agree to disagree on the accurate of the online calculator. Do you have information or links on the Toyota tach and how it can be adjusted for different engine frequency pulses.

I posted how to do it in the V8 swap thread, which is a massive thread unlikely read by someone doing a cummins swap.

Here it is in my own thread, but towards the end of the post: Builds - LX450 "Rex" Build - https://forum.ih8mud.com/threads/lx450-rex-build.1254004/page-6#post-15340174

and this post as well: Builds - LX450 "Rex" Build - https://forum.ih8mud.com/threads/lx450-rex-build.1254004/page-6#post-15496321

 

[Dubbinchris]

I posted how to do it in the V8 swap thread, which is a massive thread unlikely read by someone doing a cummins swap.

Here it is in my own thread, but towards the end of the post: Builds - LX450 "Rex" Build - https://forum.ih8mud.com/threads/lx450-rex-build.1254004/page-6#post-15340174

and this post as well: Builds - LX450 "Rex" Build - https://forum.ih8mud.com/threads/lx450-rex-build.1254004/page-6#post-15496321

Oh nice, good info for my upcoming swap.

 

[Ditcherman]

Thank you for the information on the Toyota tach. Friend, I’m happy to agree to disagree on the accuracy of the online calculator. Do you have information or links on the Toyota tach and how it can be adjusted for different engine frequency pulses.

Not to be argumentative in any way, but I was thinking as I read the previous few posts that I would try to accurately measure my loaded radius, and calibrate my tach off what the calculator says it should read.

You must have read something very convincing about the calculators not being accurate?
It’s just math, to me.

 

[Major Tom]

Not to be argumentative in any way, but I was thinking as I read the previous few posts that I would try to accurately measure my loaded radius, and calibrate my tach off what the calculator says it should read.

You must have read something very convincing about the calculators not being accurate?
It’s just math, to me.

Is there a process for measuring the loaded radius?

 

[Ditcherman]

Is there a process for measuring the loaded radius?

Sure. Load up. Measure from the center of the axle to the road.

 

[Major Tom]

The online calculator is just a mathematical equation, and it is accurate in my experience. In manual trans, tire size, 5th gear ratio, final drive ratio, and in your case the 10% OD in your transfer case are all fixed factors, there is not much variable factors in this case, so the calculation should be fairly accurate.
my previous screen shot did not take into consideration of your 10% OD, if I do, then it would make your final drive around 3.2.
View attachment 3896500
You should be no where near 2k rpms if you are doing 70.

I learned a lot reading your threads and planning on getting the 10% OD and 3.55 gears myself after reading your posts. that's why when you mentioned the rpms at higher speed, something does not line up to me there.

Thank you for the questions. I think I might have a figured out what’s missing.

NV4500 5th gear ratio GMC vs Dodge (0.85:1 vs. 0.73:1).

My nv4500 is from a gmc gasser. I changed the input shaft and bellhousing to a Dodge. It is possible that the transmission has the 0.85:1 fifth gear (trying to find the specific info on the transmission right now). This would change the rpm output.

I’ll put a Dodge fifth gear in it and let you know how it performs.

 

[Ditcherman]

Thank you for the questions. I think I might have a figured out what’s missing.

NV4500 5th gear ratio GMC vs Dodge (0.85:1 vs. 0.73:1).

My nv4500 is from a gmc gasser. I changed the input shaft and bellhousing to a Dodge. It is possible that the transmission has the 0.85:1 fifth gear (trying to find the specific info on the transmission right now). This would change the rpm output.

I’ll put a Dodge fifth gear in it and let you know how it performs.

Has it had the dreaded 5th gear nut fix done yet? If it has and it’s a good fix, is it worth messing with? From my understanding, lots of people have lots of different solutions and a few are actually long term. I made a judgement call to not mess with mine, it looked like a good fix.

You could also run a mile test in 4th gear instead of 5th, where the ratio is known.

 

[Major Tom]

Has it had the dreaded 5th gear nut fix done yet? If it has and it’s a good fix, is it worth messing with? From my understanding, lots of people have lots of different solutions and a few are actually long term. I made a judgement call to not mess with mine, it looked like a good fix.

You could also run a mile test in 4th gear instead of 5th, where the ratio is known.

I put the modified mainshaft in the transmission back in 2021. I forget what we did on the 5th gear nut. I’ll look at the fifth gear if I have to pull the tail housing off and verify the ratio. I’m happy with the way it’s running. I’m going to route a temporary ‘tiny tach” into the truck and measure rpm’s at highway speed and compare to the DDB calibration and see if I need to adjust the setting.

 

[Major Tom]

The online calculator is just a mathematical equation, and it is accurate in my experience. In manual trans, tire size, 5th gear ratio, final drive ratio, and in your case the 10% OD in your transfer case are all fixed factors, there is not much variable factors in this case, so the calculation should be fairly accurate.
my previous screen shot did not take into consideration of your 10% OD, if I do, then it would make your final drive around 3.2.
View attachment 3896500
You should be no where near 2k rpms if you are doing 70.

I learned a lot reading your threads and planning on getting the 10% OD and 3.55 gears myself after reading your posts. that's why when you mentioned the rpms at higher speed, something does not line up to me there.

Good luck on your build. I’m happy to help in any way.

I do want to make a suggestion…..

I recommend you first install the 3:55 gears and drive/test it. If you still want the 10% overdrive, do that second.

I first did the 10% install thinking it would get me in the right range. After doing it, I wasn’t happy and then went to the axles.

 

[Major Tom]

While running two electric fans on my radiator, I figured out I wasn't getting enough air across my condenser for my AC to work well here in the dirty south. I cut my motor mounts and moved the motor back to give me clearance for the Dodge mechanical fan. Now I'm getting good flow across the condenser and the AC is blowing cold. I also relocated my dryer to an area beside my battery. I had a few lines modified for the relocation. Lastly, I installed a pusher fan on my condenser. It's yet to engage so the Dodge fan must be working well.

 

[Major Tom]

what's EGT in each of these situations?

I just now got my EGT gauge up and going. I just ran 70-80 mph on I-40 in Oklahoma and Arkansas and averaged 17 mph. The EGT’s stayed between 700 and 800 degrees. When I would lay down on it, the EGT’s would hit around 950 degrees.

 

[duece71]

I just now got my EGT gauge up and going. I just ran 70-80 mph on I-40 in Oklahoma and Arkansas and averaged 17 mph. The EGT’s stayed between 700 and 800 degrees. When I would lay down on it, the EGT’s would hit around 950 degrees.
View attachment 3902146

Inter cooling is definitely the way to go. My EGT is similar but if I put a foot into it to pass, EGT shoots up to 1050-1100F.

 

[William839]

Inter cooling is definitely the way to go. My EGT is similar but if I put a foot into it to pass, EGT shoots up to 1050-1100F.

Where is your egt gauge mounted pre turbo or post ? The “most accurate spot” is towards #6 pre turbo that will give you the highest temps

 

[Major Tom]

Where is your egt gauge mounted pre turbo or post ? The “most accurate spot” is towards #6 pre turbo that will give you the highest temps

Here’s where I mounted mine.

 

[Major Tom]

Inter cooling is definitely the way to go. My EGT is similar but if I put a foot into it to pass, EGT shoots up to 1050-1100F.

What type motor setup are you running? Do mind posting a photo of your truck/motor setup?

 

[duece71]

What type motor setup are you running? Do mind posting a photo of your truck/motor setup?

1-HDT….all stock.