7.3 1992 fuel mileage - Diesel Forum

mf8n · 05-19-2005, 10:15 AM

This is my first diesel Im building a truck with a 1992 7.3 non turbo I have a 3.73 rear end at 65 mph truck is turning 2560 rpm could someone help me out what is a good rpm for good fuel mileage?

flacko93 · 05-19-2005, 10:58 AM

With that rear-end those rpm's seem high at 65 MPH. Is your speedometer accurate? My 93 dually with a 4.10 rear-end turns about 2350 rpm at 65 mph. I find my best mileage is doing between 55 to 62 with rpm's from about 2000 to 2200. Empty I get about 17 mpg on the interstate, 15 in mixed driving. Pulling my 7500 lb trailer through rolling hills on the interstate going 60 to 65 I got about 10.5 mpg.

mf8n · 05-19-2005, 11:47 AM

Does your 93 have an overdrive trans?

Greg77 · 05-19-2005, 12:27 PM

If your turning that high of rpms you must have a C6 transmission. You won't get very good milage with the setup unless you go to a gear vendor or US gear overdrive setup. Mine with a C6 runs at least 2 mpg's or more less than my five speed. Same gear ratio's 3.73 in both.

Greg

mf8n · 05-19-2005, 12:54 PM

trans I have is an allision 545 4 speed auto with no overdrive, I was thinking about going to a different rear end gear if I could get a 3.07 it would drop my rpms at 65 to 2150

CaverDave · 05-19-2005, 01:10 PM

[ QUOTE ]
trans I have is an allision 545 4 speed auto with no overdrive, I was thinking about going to a different rear end gear if I could get a 3.07 it would drop my rpms at 65 to 2150

[/ QUOTE ]

Interesting! What is the Allison behind?

mf8n · 05-19-2005, 01:20 PM

1992 7.3 non turbo. I have taken a 1988 E-350 chassis mounted a 1992 7.3 with an allision 4 speed auto. The cab and sheet metal is a 1956 cabover, the rear end gear is a 3.73 and with out an overdrive I feel my rpms are to high 2550 at 65mph. This is my first diesel engine, wanting to get the rpms dowm to get decent mileage any ideas?

chumstone · 05-19-2005, 01:34 PM

Gear Vendor, Get from Camping World, Cheapest price $2450 + ship. No other way to get fuel economy except driving at 2000 rpm or less, 50 mph. [img]/ubbthreads/images/graemlins/bleh.gif[/img]

Neal J. Moran · 05-20-2005, 08:38 PM

How tall are the tires? Taller tires will definitely help.

beretzs · 05-21-2005, 01:16 PM

Personally, If I could do it again, I would probably look towards the US Gear OD. It seems to be a little heavier and built a little stronger. There is nothing wrong with the GV, just not as beefy as the US Gear. Either one of those will drop your RPMS 500 at any given speed. Good luck. Scotty

AggieDiesel01 · 05-21-2005, 02:05 PM

I think you can order just about any gear size you want from a good supplier. I believe max torque is made around 1850 rpm so I would think that this would be the best place to max out fuel MPGs. I think you are right about changing the gears this is the easiest way to lower your RPMs and if you do them your self they should be as cheap or cheaper than changing tire size. BTW 2150 is about where my truck is going 70.

Also if you get a chance post some pics of your rig. I think people here would enjoy seeing it.

hweaver · 05-21-2005, 10:35 PM

Dang, my 84 F-250, 4X4, 4 speed, 4.10 ratio differential turns around 2900rpm at 65mph. I try to keep it around 2500rpm which is 55mph. Luckily, I don't need to drive on high speed roads, since we don't have any in Alaska.]

I wish I had an overdrive for the old beast, but maybe someday.

hweaver