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KurtVW
Dodge Dakota
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3/31/2004
23:00:12
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 Subject: High Cruise RPM
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Hey all,
I recently upgraded from my 2001 V6 to a 2004 V8.
I'm surprised to see that my cruise at 70mph in the v8 results in a slightly higher RPM than the V6 truck and I'm a little curious about that. Most of my past experience with V8 (I admit my last V8 was a '70's model) says that V8 rpm at cruise is lower since they are geared for the extra power.
My rig is the 4.7 with the 5-speed manual and a 3.55 rear end. The old one was a 3.9 Auto, not sure the rear.
At 70mph the v8 is turning about 2100-2200, and that just seems like a lot of spin for a V8 to be pulling for a long drive.
I know, I know, its OHC and all that.. But I'd sure feel better hearing one of you 60k mile owners tell me that its always been that way and the motor doesn't care.
P.S. Don't bother filling me in on sludge and other 4.7 woes, I read more than I post and I know all about that. I'm just interested in the wear and tear at this engine speed.
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99DAK
Dodge Dakota
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3/31/2004
23:09:53
| RE: High Cruise RPM
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5th gear on the NV3500 manual is 0.73:1, OD on the auto is 0.69:1 - consider tire size, too.
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Sephiroth
Dodge Dakota
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3/31/2004
23:52:47
|  RE: High Cruise RPM
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I have a '95 V8 5.2L, and I can cruise 65mph at about 1700-1800rpm. Dunno' why yours is cranking so high with the 3:55, which I also have. You have bigger tires than I do, though.
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WipLash
R/T
4/01/2004
00:17:57
| RE: High Cruise RPM
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Yeah,
The auto behind the 3.9 has a .69 OD. Even if you had an auto behind the 4.7L (45re) it would only have a .71 OD. You would barely notice a difference between a .69~.71~.73. Yor new 4.7L more than likely has bigger 16" wheels and tires than your old 3.9L which probably had 15" wheels and tires. It is more than likely your tach. It is there for looks. The PCM controls the rev limit. They stick the tachs in their just because everyone else has a tach. My tach was off by 400rpm @ 80mph. I wouldn't put much faith in the tach until I had it on a chasis dyno to compare the real RPM to what your tach says.
When I dynoed my truck my tach never got over 4900rpm, but the dyno said I hit 5250rpm.
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Rob C
Dodge Dakota
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4/01/2004
02:33:51
| RE: High Cruise RPM
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KurtVW, I've got 3.73 gears and I cruise at about 2400 rpm when doing 70. Some Dakotas have the 3.92 gears which would rev even higher at 70. I don't think it's causing excessive wear.
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Bowtie-ZL1
Dodge Dakota
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4/01/2004
06:15:53
| RE: High Cruise RPM
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"At 70mph the v8 is turning about 2100-2200, and that just seems like a lot of spin for a V8 to be pulling for a long drive."
Quite normal for me.
I have a 2002 Dak with the 4.7, 45re, 3.55's and 30" tires.
I do not drive too much at 70 but at 80 I turn about 2400-2500 rpm. I drive 650 miles per week at this rpm and have done so for the last 30,000 of 48,000 total miles. I have experienced no problems. I have cut open and examined three oil filters and have have found no metal particles so I am no concerned with the RPM level.
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99DAK
Dodge Dakota
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4/01/2004
11:09:17
| RE: High Cruise RPM
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"You would barely notice a difference between a .69~.71~.73."
>5% difference between .69 and .73, which @ >2000rpm is a >100rpm difference.
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99DAK
Dodge Dakota
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4/01/2004
11:13:16
| RE: High Cruise RPM
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"Yor new 4.7L more than likely has bigger 16" wheels and tires than your old 3.9L..."
Bigger tires would result in lower cruising RPMs, not higher.
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huskerpt
Dodge Dakota
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4/01/2004
17:07:23
| RE: High Cruise RPM
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I have a 2001 4.7L 4x4 QC with 60000 miles. I Drive 80 miles a day. At 70 mph I run in that 2100-2200 mph. I think you are going to be fine.
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WipLash
R/T
4/01/2004
20:26:50
| RE: High Cruise RPM
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99DAK,
DUH.....
100rpm is barely noticeable since the tick marks on the tack are graduated at 125rpm and the width of the needle is almost 50rpm....
Also, no one has said anything about larger tires raising the rpms. Are you on some good hallucinogenics or are you just naturally schizophrenic?
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99DAK
Dodge Dakota
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4/01/2004
23:23:22
| RE: High Cruise RPM
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I can clearly see 100 rpm differences on my tach - maybe you need (new) glasses.
As for the tires, OP said "I'm surprised to see that my cruise at 70mph in the v8 results in a slightly higher RPM than the V6 truck and I'm a little curious about that."
To which you responded "Yor new 4.7L more than likely has bigger 16" wheels and tires than your old 3.9L which probably had 15" wheels and tires."
Looks like you might be the one with a drug problem.
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WipLash
R/T
4/01/2004
23:41:57
| RE: High Cruise RPM
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99DAK,
I guess you didn't read the rest of the post. Or maybe you can't read.
I said.....
"It is more than likely your tach. It is there for looks. The PCM controls the rev limit. They stick the tachs in their just because everyone else has a tach. My tach was off by 400rpm @ 80mph. I wouldn't put much faith in the tach until I had it on a chasis dyno to compare the real RPM to what your tach says."
I was making a point that since his new truck has bigger wheels and tires that the rpms should be lower not higher. This would suggest that his tach is out of calibration. I said nothing about the larger tires raising the rpms.
You need to read the post and take them for what they say instead of adding sh!t to it for the sake of arguing.
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Ian
Dodge Dakota
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4/02/2004
01:06:36
| RE: High Cruise RPM
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Wow...I have never heard someone concerned over cruising at 2100-2200 rpms...Wow! What would you have it at sir, 500 rpms?
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Kurtvw
Dodge Dakota
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4/02/2004
01:38:18
| RE: High Cruise RPM
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Not concerned Ian... Curious.
My previous V8s of the distant past would tick along on the highway at about 1700-1800... even my V6 Dak was under 2000 until 70mph.
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Rob C
Dodge Dakota
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4/02/2004
03:18:30
| RE: High Cruise RPM
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Kurtvw, were your previous V8's in trucks? V8's generally produce more torque at lower rpm than V6's. So, in passenger cars you'll see higher final drive gearing resulting in lower cruise rpm. This is fine for a vehicle than isn't going to haul more than 4-5 people but, in a truck you need torque and lower gearing so you can haul trailers or even heavy loads in the bed.
I had a V8 Mustang and at 60 I was only turning 1750 rpm but, in a truck you're not likely to see .70 OD gear and a 3.08 rearend gearing.
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99DAK
Dodge Dakota
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4/02/2004
10:20:22
| RE: High Cruise RPM
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Wiplash-
An admirable attempt to put a positive spin on your bonehead post - not a very good one, but a nice try none the less.
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99DAK
Dodge Dakota
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4/02/2004
10:58:26
| RE: High Cruise RPM
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Sorry, I know this is beating a dead horse, but I just can't resist.
"I was making a point that since his new truck has bigger wheels and tires that the rpms should be lower not higher."
OP said NOTHING about tire size on either truck.
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actually
Dodge Dakota
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4/04/2004
18:42:36
| RE: High Cruise RPM
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whiplash as soon as you mentioned the 16 vs. 15 inch tire thing you implied that was one of the reasons there is a difference, AS soon as you put in the period between the comment about the wheels and the tach the meaning changed. no use in lying and trying to back track out of it you said it and that's all that matters. Once again you have proven your lack of knowledge, sisnce you seem to be one of those that cannot handle being wrong, maybe you should keep your mouth/keyboard shut and let us think you to be an idiot, instead of opening it at every oppertunity and proving it.
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WipLash
R/T
4/04/2004
21:10:00
| RE: High Cruise RPM
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99DAK,
The point of my reply was to tell him is tach was out of calibration. I did say that very clearly.
I mentioned the tires size because I owned a 2001 3.9L SLT and I know that they come standard with 215/75/15. I also owned a 2002 4.7L SLT and they come standard with 255/65/16. Many 2002's had 265/65/16 tires (mine did). Therefore, since both had 3.55's in the rear the 4.7L should have had a lower rpm at the same speed as the 2001 3.9L. He said it was reading a higher RPM. That is impossible.....
Therefore, I suggested that he take it to a shop with a Chassis Dyno to compare the tach reading to the real RPMs and recalibrate it. I also pointed out that mine was off 400rpm.
Did I not say that?
Why would I tell the guy to get his tach calibrated if I was implying that it was his tires giving him a bad rpm reading?
You are trying to put a spin on something that there is nothing to spin except a chassis dyno to calibrate his tach.
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99DAK
Dodge Dakota
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4/05/2004
02:44:20
| RE: High Cruise RPM
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WipLash-
Not spinning anything, quite the opposite, I'm trying to stick to known facts and stop the assumptions that are not supported by the original post.
For instance, the 2001 could have had larger-than-stock tires, or the optional 235/75/15, which is only 2% smaller circumference than the 245/70/16 (one of the standard 2004 sizes). All other things being equal, 2% @ 2000rpm is only 40rpm, and you already said you considered 100rpm difference negligible. And again, that's assuming the V6 truck didn't have larger tires (my CC SLT 4x2 had 30x9.50/15 tires on it when I got it, but original equipment was 255/65/15, a 2" shorter tire). So your assumption that his newer truck has larger tires is just that, an assumption.
Also the fact that he clearly said he didn't know which rear end gears the V6 had - if they were 3:21 gears that, in itself, could explain the rpm difference.
Experience has taught me to look for mundane explanations before looking for problems that may not exist.
As to your question: "Why would I tell the guy to get his tach calibrated if I was implying that it was his tires giving him a bad rpm reading?"
You obviously wouldn't, because tire size would only skew his odometer and speedo, not the tach.
The problem with this whole discussion is that the RPM difference he's seeing is almost certainly due to a combination of things, specifically: different transmission ratios, possibly different rear end ratios, and quite probably different tire sizes. So we could continue to speculate until the cows come home - and I don't hear any mooing yet.
Peace.
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matt
Dodge Dakota
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4/05/2004
18:45:23
| RE: High Cruise RPM
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i have a 94 dakota, and cruising at 60mph it turns 2000 rpm's. this seemed a little high to me does anyone have a 94 dakota, 5.2L 4x4 that could tell me what your turning. the tires are like 29" if that has something to do with it
thanks
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