Changing gear ratio?
Thread Starter
|
New User
Joined: Oct 2006
Posts: 1
Likes: 0
Changing gear ratio?
I have a F-350 dually with a 7.3 powerstroke engine and was thinking about changing my gears. I have 4:10 gears now and can get gears rated at around 3:55 to go back into it. Has anyone done this? If so how much fuel mileage if any can I gain by doing this? I know I will lose some power, but i do not pull as much as I did once anyway and I have some to spare anyway. I also get about 13 to 14 mpg now and was hoping this would help. the one thing i notice now is that when we do go on trips that when I am running out on the interstate around 75 to 80 mph that the rpms are 2700 or more. I have been told that 3:55 would drop that down to maybe around 2100 rpms at them speeds. Just looking for some better fuel mileage and any help is wanted! Thanks
Lead Driver
Joined: Jun 2007
Posts: 6,757
Likes: 5
From: Corvallis, OR
Wind resistance goes up at the square of velocity, power required from your engine goes up at the cube of velocity. Slowing down will make a huge difference in mileage, so if you can keep it around 65 that would help a lot. Also, 2700 rpms is way over the peak torque of the 7.3, so thats not an efficient place to run it. Peak torque is around 1600-1700 rpms, so the optimum gear ratio for running 75-80 as you listed above would be under 3.0, which don't exist. Changing to 3.55s would really hurt your low end power, but if you don't tow much it may not be an issue. 3.73s would be only a 10% change, so your 2700 rpms would come down to around 2430 rpms.
The gear change would help, but you'll see a bigger improvement by slowing down. I ran 80 all the time when I had my Intrepid, but now that I'm in a truck I set the cruise at 65-70.
The gear change would help, but you'll see a bigger improvement by slowing down. I ran 80 all the time when I had my Intrepid, but now that I'm in a truck I set the cruise at 65-70.
Postmaster
Joined: May 2008
Posts: 3,099
Likes: 0
From: horicon Wi
my $.02 i'd go for it if you only tow every now and then and what you tow isn't very heavy. besides if you get the knowledge you might be able to change ratios in a day by your self. might want to look for 3.42 gears. and by the way if you are thinking of changing ratios by your self i would buy an old ford dana 60 axle and practice taking the ring gear out. Just a thought.
Thread
Thread Starter
Forum
Replies
Last Post
cwheeler96
1994.5 - 1997 7.3L Power Stroke Diesel
1
Jun 27, 2014 07:46 PM
Macrobb
1987 - 1996 F150 & Larger F-Series Trucks
11
Jan 12, 2012 09:34 AM
Nightrain
Clutch, Transmission, Differential, Axle & Transfer Case
16
Aug 17, 2006 01:56 PM
chipper
1999 - 2003 7.3L Power Stroke Diesel
9
Mar 23, 2005 06:34 PM
