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fast80cc
Dodge Dakota
7/11/2001
13:27:46
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 Subject: Redline/Curves for 3.9L
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Message:
Can anyone point me to HP/Torque curves for a stock Gen-III (2001) 3.9L? I remember seeing them in the CC brochure (crank HP), but would like to see some rear-wheel dyno numbers. I'd like to make some simple mods. (intake, exhaust, TB) and would like a baseline.
Also, what is the redline (I assume there's a rev. limiter in the PCM) for the 3.9L? The tach has NO indication of this at all (really STUPID)! Where does the HP curve really start to drop-off. The thing seems to pull up to 4000. I've only got 1000 miles on it, so... Seems to get LOUD above 4300 (as far as I dare rev. it on a new motor).
Finally, what kind of driveline loss (%) should I factor in on a 4x4. I've seen 20-25% for a 4x2 and assume a 4x4 will be greater. Note: I'm talking about running in 2WD here. I've read some posts about starting in 4HI (to prevent wheelspin) and switching to 2WD. Are these guys kidding?!? Sounds like a good way to break things to me!!!
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cbsdakota
Dodge Dakota
7/11/2001
14:55:59
|  RE: Redline/Curves for 3.9L
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Message:
When I hold it to the floor, my auto will shift at 4800 or 4900 but it doesn't seem to be anymore powerful than if I back off and let it shift at like 3500 to 3800 and let it get back in it's power band. If I recall the HP fell off around 4800 in the brochure. Can't help you with the 4x4. I have a 2wd.
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lattimer
Dodge Dakota
7/11/2001
18:16:14
| RE: Redline/Curves for 3.9L
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Message:
The redline for the 3.9L is 5500. The rev limiter on mines will shut it down at about 5200. I seem to get the best power from 2800 up to 4600. She shifts at 4800 at WOT, so I usually work the gas a litlle to make it shift a little short.
BTW, my tach (2000 Dak 3.9L 4x4 CC)has yellow and red markings on it. I have heard of some trucks that didn't, so I guess you are just in that unlucky bracket.
Driveline loss for the 4X4 is somewhere around 28%-32% (Auto Tranny) running in 2wd. A 4X2 is around 24% (Auto Tranny). This assumes all components in good condition. You also lose a lot more at take off due to axle wrap, compression of the springs, etc.
Also, shifting out of 4x4 under power won't really hurt much except you ET. The gears and whatnot will not unmesh until the torque is let off. Now shifting in under too much power or at too high of speed will wreck stuff. Trust me. Thats how the torture tests are done for the transfer cases At New Venture Gear.
Shawn
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fast80cc
Dodge Dakota
7/11/2001
18:41:27
|  RE: Redline/Curves for 3.9L
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Message:
Thanks for the input! I forgot to mention that I have a 5-spd. I assume the driveline losses are slightly less than with an auto. Is it actually possible to shift into 4HI under "too much power or at too high a speed"? I was hoping that the PCM would protect me from myself here!?! I know that it won't let me shift into 4LO unless I'm nearly stopped. I haven't yet dared to try shifting into 4HI while doing 70 down the freeway. I assume this would be bad!!! I hope that the 4HI light would just blink at me saying "not NOW you idiot" like it does for 4LO. Funny, the manual doesn't say what the UPPER speed limit is to switch into 4HI (if there is one).
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lattimer
Dodge Dakota
7/12/2001
17:28:23
| RE: Redline/Curves for 3.9L
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Message:
I forgot you have a 2001. My 2000 has the lever on the floor, so with enough force it has two choices, either shift in or break something. I'm not certain on the electric shift models.
With your 5-speed, you should be in the same loss area as a 4x2 auto. I'm still kicking myself for not taking the 5-speed truck when I had the chance. I passed up a really good deal just because it didn't have power windows, so I took the auto.
BTW, my manual says not to shift to 4x4 over 55 mph. Like I would need it or want it at that speed!! Again, I'm not sure about your truck. The computer may protect you, but I personally wouldn't tempt fate.
Shawn
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