I've noticed that most of you have stated that at 70 mph you are turning 2000 rpm's. My truck (04.5 CC Dmax) turns 2200 at 70 and I am only getting about 18 mpg highway. I've checked this several times and it is always 2200 at 70 mph. Every thing is stock with 3.73 rear end. Why would my truck be turning 200 rpm more than everyone else? Just curious.

stock size tires vs. oversized tires maybe...

285 Revos on mine.

No, my tires are stock 245's

my truck also turns 2200 rpm @ 70mph with the stock tires

i must add .... my 05 with 265 's turns
approx. 2200 rpms i also have a 02 for a work truck , (completely stock) and it
turns less than 2000 rpms at 70mph !
it has 245's on it ??????

some one input ??
the05hd

No, my tires are stock 245's
Sorry, that is what i meant, you may be running stock tires when others are not.

I have heard tranny slipage could be the culprit. Hopefully we will start something here.

It might be in the tach. After getting a new cluster this winter the new tach reads 100rpm slower than the original at any and all speeds.

stock 05 2000rpm at 65

stock 05 1800 rpm @ 60

can you use the predator to check the RPMs while driving to see if the in dash tach is reading correctly?

stock 05 2000 rpms gets me 65 mph..... predator at 65 setting gets 2000 rpms and 65 mpg

towing 8K TT 2000 rpms gets 65......

stock 05 2000 rpms gets me 65 mph..... predator at 65 setting gets 2000 rpms and 65 mpg

towing 8K TT 2000 rpms gets 65......
And you guys thought some of these other mileage claims were high! :lol:

2200 rpm with my 285's gets me to 75mph. My speedo is corrected but it's just a hair fast, like 1 or 2% I got lazy when I got it that close ;)

If you say that slipping can have something to do with it, have you tried to put your truck into tow/haul to lock the tq converter and see if the RPMs are the same?

3500 SRW's are 2000 @ 70mph.

Except Big Blue:

http://fuzzydiceracing.com/k/speedo1.jpg

I'm going for the land speed record in a production diesel.

Until you get your speedometer fixed anyway....

i'd say i'm 2200+ on stock 245's

And you guys thought some of these other mileage claims were high! :lol:NO NO its true I swear it !!:D :lol:

70mph on stock 245's = 2200 rpm give or take a few on my truck. Confirmed with Autotap reading rpm directly from pcm.:) Wish that double overdrive retrofit kit for the allison (6th gear) would hit the market so I could lower that closer to 1900 rpm at the same speed. What I've found on my truck is that as soon as I cross the 2000rpm barrier, the MPG on the truck drops from 19.5 on the highway to less than 18.0 mpg. The "sweet spot" on the DMAX is 1800-1900 for fuel economy (in my personal opinion)

My 2004.5 turns 2000 at 65, 2200 at 70 on stock 245's.


2004.5 LLY, CC SB

2100 rpm's @ 70mph

Thanks for the input guys. I feel a little better now. And I agree - push it too far past 2000 rpm's and the mpg's start to fall.

Not to hijack the thread but what is the latest on the 6spd alli??

As to the spd Q. some people have taller tires with the speedo corrected and some do not. 285s@70=2000ish give or take 50 rpms

great pic mcrat.

70 MPH @2200 RPM W/Banks on Level 4, Stock Tires

2100 RPM's @ 70 MPH about 2000 @ 68 MPH with 265's

Between 1900 and 2000 @ 70mph

My 2004.5 turns 2000 at 65, 2200 at 70 on stock 245's.


2004.5 LLY, CC SB
:exactly:

I've noticed that most of you have stated that at 70 mph you are turning 2000 rpm's. My truck (04.5 CC Dmax) turns 2200 at 70 and I am only getting about 18 mpg highway. I've checked this several times and it is always 2200 at 70 mph. Every thing is stock with 3.73 rear end. Why would my truck be turning 200 rpm more than everyone else? Just curious.
Stock tires and stock gears should be right at 68 mph @ 2,000 rpm. The 3500 single rear wheel setup will be different then 245`s on the 2500HD
And stock gears with 285`s on a 2500HD will be about 74 mph at 2,000 rpm,.
This is in 5th gear when the transmission is warmed to operating temp.

my truck also turns 2200 rpm @ 70mph with the stock tires

Are you allowing the transmission to warm to above 100* before checking the rpm at speed? Because if the transmission is under 100* (Plus or minus 10*) it is not locked in, and the rpm will be about 300 rpm higher.

Originally Posted by Rob147
My 2004.5 turns 2000 at 65, 2200 at 70 on stock 245's.


2004.5 LLY, CC SB
Same as stated above but on my 2005 with 523 miles on it... It don't get any stocker than that.

Both of mine turn around 2200 at 70

Just some simple math:
With stock 245s (which have a circumference of 95.72 inches) we should see 2045 RPMs at 70 miles/hour:

70 / 60 = miles/minute
70 / 60 * 1760 * 3 * 12 = 73920 inches/minute
73920 / 95.72 = 772.25 tire revolutions/minute
772.25 * 3.73 = 2880.5 propellershaft revolutions/minute
2880.5 * 0.71 = 2045 RPM (5th gear ratio Allison locked up)

Looks like mine is turning little faster also - either the display is off or the tires have a smaller circumference, I assume the tires are the culprit... :exactly:

Bang on the dash until you get the Tach reading you want.

kind of odd my rpm is at 1800 at 70 mph . maybe because of my 38.5 inch tires .

I have 265's and confirmed 2050 rpm's @ 70 MPH with the Attitude and a Tech II. The gage reads about 2100 though.

Hey McRat - Looks like your loosing that race? :eek: What Gives!?!?!?! You are one of my idols and now I'm bummed ;) !

You guys aren't thinking, your tach and speedo don't know what size your tires are,you would get the same readings if you were on jack stands.
Your instruments are likely to be out by that much, no need to worry, your tranny's fine.

I have 265's and confirmed 2050 rpm's @ 70 MPH with the Attitude and a Tech II. The gage reads about 2100 though.

Hey McRat - Looks like your loosing that race? :eek: What Gives!?!?!?! You are one of my idols and now I'm bummed ;) !


That's Dmax Doug ahead of me. His truck is FAST!! :eek:

But I got to the destination first, even towing a 22' trailer. :D

That's Dmax Doug ahead of me. His truck is FAST!! :eek:

But I got to the destination first, even towing a 22' trailer. :D
:) Wheeew. I feel much better now!:cool2:

Just checked today. At 70 mph I'm showing 2200 rpm's.

I get 2400 rpm on 245's at 70 going north. 1800 rpm at 70 going south, all down hill ya' know!

2200 @ 70mph

This is what I have to say about McRats pic http://www.dieselplace.com/forum/images/smilies/drop_mouth.gif

http://www.dieselplace.com/forum/images/smilies/cool2.gif

I get 2400 rpm on 245's at 70 going north. 1800 rpm at 70 going south, all down hill ya' know!
That shouldn't matter unless the transmission shifts down going North. And the hill would have to be huge to down shift if you are running empty. :eek: Besides that, 245`s will yeld higher then 2400 rpm running in 4th at 70 mph :confused:

With stock 245 tires and 3.73 gears you will run just a shade over 33 mph per 1000 rpm in 5th gear with the converter locked up. So at 70 you should be turning a bit over 2100.

Checked this AM when no wind and a loooooong flat section of I80. 2100 RPM with the 285s at 42psi.

2100 rpm's @ 70 mph, tire size = 285's.

Some of these tachs are way off. Our trucks should be running 2,000 rpm at 73 mph on 285/75/16" tires. 68 mph on 245`s, and 70.5 mph on 265`s.

2100 rpm's @ 70 mph, tire size = 285's.

Some of these tachs are way off. Our trucks should be running 2,000 rpm at 73 mph on 285/75/16" tires. 68 mph on 245`s, and 70.5 mph on 265`s.
hdmax - is the live data scan from the predator more accurate than the needle?