Speed vs. RPM - PowerStrokeNation : Ford Powerstroke Diesel Forum
 
LinkBack Thread Tools Display Modes
post #1 of 9 (permalink) Old 11-26-2007, 01:59 AM Thread Starter
4x4
PSN Local
 
Join Date: Oct 2007
Location: Portland, Oregon
Posts: 117
Speed vs. RPM

Took my truck on its first hwy trip, about 300 miles. Looks like about 15 mpg. I noticed that, compared to my late SD, this truck seems to be geared lower somehow when cruising in OD. Going down long grades in the SD it seemed I could take my foot off the pedal and the truck would roll well on its own, maintaining hwy speeds for some distance without slowing down. In the OBS I felt like I needed another gear almost and had to keep power on to maintain speed.
On flat windless hwy I would cruise at 60 mph at about 1900 rpm. I'm betting that, like the SD, the 35's are causing my indicated speed to read about 9% low so I'm probably moving about 65 mph. Do these numbers seem normal for the 3.73 (?) rearend that I think I have?

Steve

1996 F350, CC, LB, 4x4, 4" lift, 35" MT's, 4.10, 3" DP, Tymar in.....
4x4 is offline  
Sponsored Links
Advertisement
 
post #2 of 9 (permalink) Old 11-26-2007, 02:11 AM
Don't EFN worry about it
 
Aljay's Avatar
 
Join Date: Jul 2007
Location: Fort Worth TEXAS Damn it !!
Posts: 15,588
Re: Speed vs. RPM

bet you have 4:10 gears.

97 crew cab shorty-4x4 Lots of mods .
Tuned by T Wildman
Aljay is offline  
post #3 of 9 (permalink) Old 11-26-2007, 02:20 AM
DILLIGAFF
 
Join Date: Sep 2007
Location: G-ville, Flo-rida THE GATOR NATION
Posts: 5,946
Send a message via AIM to Redfish
Re: Speed vs. RPM


2006 F-250 CC King Ranch, Harley Headlights w/ 55w HIDs
ARP studs, MBRP 4" exhaust and AM Colbalts By:
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
, AFE stg. 2 Pro Guard 7 from XDP, SCT from innovative!
14.09 @ 94 1.85 60'

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
~
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


Redfish is offline  
 
post #4 of 9 (permalink) Old 11-26-2007, 05:02 AM
OBS junkie
 
Cat_Rebel's Avatar
 
Join Date: Jul 2007
Location: In or under a truck
Posts: 8,250
Re: Speed vs. RPM

3.55s or 4.10s for the OBS. The "drag" you describe is part of the 4.10 gearing, they like to cost down & cruise around 30-35mph. When you get used to it you'll find you don't have to hit the brakes as much as you would with a truck geared higher. 15mpg sounds about right, that's about what my old IDI does & what other OBS Powerstrokes with 4.10s I've seen will do.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

97 F350 CCLB "Da Bus"

RIP Will Iott
"This ain't no practice run"


Quote:
Originally Posted by countryboyrob View Post
And remember, he's cat rebel....he doesn't do it the normal way.
Cat_Rebel is offline  
post #5 of 9 (permalink) Old 11-26-2007, 02:02 PM Thread Starter
4x4
PSN Local
 
Join Date: Oct 2007
Location: Portland, Oregon
Posts: 117
Re: Speed vs. RPM

I guess that explains why the tag on the diff. says 10 10 xxx. I don't know how I missed that before buying the truck. Although I have to say that, as a daily driver, I kind of like the off-the-line quickness that this truck has over the SD and I am assuming it is the gearing that causes this.
Seems that 3.55 to 4.10 is quite a jump. I'm not sure I'd want the 3.55 with the larger tires. Tradeoffs I guess?

Steve

1996 F350, CC, LB, 4x4, 4" lift, 35" MT's, 4.10, 3" DP, Tymar in.....
4x4 is offline  
post #6 of 9 (permalink) Old 11-26-2007, 06:42 PM
OBS junkie
 
Cat_Rebel's Avatar
 
Join Date: Jul 2007
Location: In or under a truck
Posts: 8,250
Re: Speed vs. RPM

How large of a tire do you want to go with? If you make a good amount of power & don't tow anything too large a set of 3.73 might be alright for you. It just really depends what your trying to do with your truck & how much $$$ you want to spend.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

97 F350 CCLB "Da Bus"

RIP Will Iott
"This ain't no practice run"


Quote:
Originally Posted by countryboyrob View Post
And remember, he's cat rebel....he doesn't do it the normal way.
Cat_Rebel is offline  
post #7 of 9 (permalink) Old 11-26-2007, 07:45 PM Thread Starter
4x4
PSN Local
 
Join Date: Oct 2007
Location: Portland, Oregon
Posts: 117
Re: Speed vs. RPM

Cat,
I doubt I'll ever go over 35s. I'd like to try some 37 x 12.5's sometime but the 35's already rub on the leaf at full crank.
And I don't foresee any serious towing; just small utility trailers.
The more I think about it the more I think the higher gearing would ONLY benefit on fairly flat hwy and higher speeds. In the city, towing, offroad, or even on grades or winding roads I think the higher gears will have benefit.?? Basically, any time I am operating under 60 mph.

I don't want to spend money on drivetrain, other than tranny. I am getting ready for exhaust, then tranny, then gauges, then chip.

Steve

1996 F350, CC, LB, 4x4, 4" lift, 35" MT's, 4.10, 3" DP, Tymar in.....
4x4 is offline  
post #8 of 9 (permalink) Old 11-26-2007, 08:35 PM
OBS junkie
 
Cat_Rebel's Avatar
 
Join Date: Jul 2007
Location: In or under a truck
Posts: 8,250
Re: Speed vs. RPM

I think I'd stick with the 4.10s, that's what I'm running in my truck. I want to try a set of 35s on mine just to see how it acts. Generally if your doing alot of highway driving 65-75mph you'll want a set of 3.55 gears. For alot of 55mph country roads & town 4.10s arn't all that bad espically if your running larger rubber. Also considering how big of a truck your pushing down the road I'd stick with the 4.10s on your truck.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

97 F350 CCLB "Da Bus"

RIP Will Iott
"This ain't no practice run"


Quote:
Originally Posted by countryboyrob View Post
And remember, he's cat rebel....he doesn't do it the normal way.
Cat_Rebel is offline  
post #9 of 9 (permalink) Old 12-02-2007, 02:03 AM
PSN Veteran
 
mandkole's Avatar
 
Join Date: Dec 2007
Location: Ridgefield, WA
Posts: 1,623
Re: Speed vs. RPM

yup 4.10-- the tag likely says 4L10 (for ltd slip) or I think just 4 10 for open. Your 4 is probably under the bolt that goes through the tag. 65 [email protected] about 2400....

2000 F250 CCSB-- GT4294R, 250/100s, Dahl/Fuelab, PHP, scan gauge, stock 17* pump

1994 F250 4x4 SC (sold)
1997 F250 CCSB 2wd (sold)
mandkole is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the PowerStrokeNation : Ford Powerstroke Diesel Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome