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Old 02-17-2017, 10:06 AM   #1
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Question 5.9 Mechanical ?

After reading this thread i have a wonder.
http://www.skoolie.net/forums/f39/20...e-16798-3.html

I am thinking that my 5.9 has been turned up.I can run 78 mph @ 2500 rpm no problem. I have to always keep off the throttle or i am running off and running maybe 2800 rpm but always runs cool. I don't have tranny temp gauge nor a pyrometer.Am i in danger of blowing it up?
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1998 Ford B700 Thomas body 65 passenger. 5.9 Cummins 12 valve with MT643 Transmission 123,000 miles.
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Old 02-17-2017, 10:37 AM   #2
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Given that you are running 1000 rpm's over the engine's sweet spot...I'd say you have a fair chance of blowing it up. And without an EGT...even better. The older, all mechanicals only require a screwdriver to turn up the power (one point that makes them very popular) but they can easily be screwed to the point of a runaway. A condition you do NOT want to experience. I'd strongly recommend a pyrometer and a tranny gauge. If it is a 545, they are really easy to cook. Might have a Cummins tech look it over to see what has been reconfigured and where it is on the meltdown scale just to be safe.
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Old 02-17-2017, 10:42 AM   #3
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I read the 360 will run all day at 2700 rpm. This was from a mechanic. Maybe a typo?
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Old 02-17-2017, 10:48 AM   #4
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PS...an excellent source for Cummins info (from stock to mind blowing builds) can be found on the 4BT swap site below. They deal with all sorts of engines, despite the name and many experienced 6BT builders there.

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Old 02-17-2017, 11:07 AM   #5
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Quote:
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Given that you are running 1000 rpm's over the engine's sweet spot...I'd say you have a fair chance of blowing it up.
Nope.

The 6BT's sweet spot is most definitely not at 1,500 rpm.

Peak torque comes at 1,600 rpm, but hp peaks at 2,500 rpm with a redline of 3,000. He's cruising right in the sweet spot.

That's not to say that someone hasn't twisted that fuel screw though. A pyrometer is never a bad idea. But he's not spinning the engine too fast.
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Old 02-17-2017, 11:33 AM   #6
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My bad...I put the 4BT numbers up. But the "sweet spot" on a diesel is not at or near redline or max HP...it is just slightly above the peak torque number. That puts it around 1800 or so for a 6BT. Running consistently at peak HP will shorten the life of any diesel and also consume way more fuel. That is precisely the reason 18 wheelers have so many gears and you hear them scooting along at 75 at what sounds almost like idle.
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Old 02-17-2017, 11:48 AM   #7
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Is the Cummins 6bt & International dt360 the same torque/hp numbers @ the same rpm?
Just trying to clarify.
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Old 02-17-2017, 12:43 PM   #8
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Originally Posted by Tango View Post
My bad...I put the 4BT numbers up. But the "sweet spot" on a diesel is not at or near redline or max HP...it is just slightly above the peak torque number. That puts it around 1800 or so for a 6BT. Running consistently at peak HP will shorten the life of any diesel and also consume way more fuel. That is precisely the reason 18 wheelers have so many gears and you hear them scooting along at 75 at what sounds almost like idle.
Sure, that'll reduce the engine's life if you're constantly producing peak hp. But running at the rpm where peak hp is made is a different story. Running down the highway at partial throttle, maintaining 2,500 rpm is far different than being under constant heavy load.

The Cummins 5.9 was designed by Case for use in construction/industrial/agricultural equipment where the throttle gets parked wide open for hours on end with varying loads placed on it.

And OTR trucks have a tremendous number of gears and keep their rpm down because they have to. Those engines have tremendously long strokes to create massive amounts of torque, but those big strokes result in very low redlines and hp peaks. An extremely short rev range means you're constantly shifting.
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Old 02-17-2017, 12:44 PM   #9
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my DT360 is 185 HP at 2300 RPM with a Max SAFE longevity RPM of 2700. and a Max operating RPM (wont blow it up but you can cut its life significantly up to 50%!!) is 3200 RPM...

my T-444E is 190 HP at 2300 RPM. with a Max RPM (computer limited) of 2700. the Fiord guys running the T-444E's (power stroke 7.3) run them at 3400 max..

However be it that your diesel engine runs at lower RPMs than your car engine doesnt mean you want to run them all the time at their Max.. even a couople hundred RPMs off their max saves a lot of life in an engine...

the DT-360s are considered nearly indestructable albeit not real powerful as long as you dont turn up the fuel too much... many will say that adjusting the fuel screw on it and not adjusting the RPM governor up will net you a few good safe ponies.. even the Navistar service shop manual mentions greatly reduced expected lifespan by turning the governor up to 3200 RPM.. the valves float at 3400 on that motor..

I dont know much about ther expected lifespan loss in a cummins by turning up the fuel and RPM but I can only imagaine since its an inline 6 that the numbers would be similar to that of the DT-360, id rather my roadtrip take a little longer and I dont ruin my bus... or put another way... my DT-360 with only 97k miles on it (its a reman).. would cost me at least 3-4K to in frame if I ruined it or worse yet if I spin a bearing or busted a rod... for about 4-5K I can go buy an overdrive transmission and stick in it...

do the math... turn up the smoke and blow the engine or put in a transmissiuon with OD...
-Christopher
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Old 02-17-2017, 12:49 PM   #10
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(edit: ^^^ That's exactly who I had in mind when I said I'd defer. Christopher, you have a knack for showing up right on time when someone mentions the 360. )


Quote:
Originally Posted by BigDavid View Post
Is the Cummins 6bt & International dt360 the same torque/hp numbers @ the same rpm?
Just trying to clarify.
That I'm not sure of.

I know they typically have similar hp numbers, but I'm not sure what the DT360 had for a bore to stroke ratio or what the hp/torque curves looked like. I'll defer to someone else on that one.
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