Hi everyone,

brand new to the forum, but I've browsed lots before. Just retired my 1990 f250 with the 7.3 non-turbo diesel, and bought a 1994.5 f250 4X4 with the turbo diesel.

Axle code is 35, which I think means 4:10 gear ratio rear end. Trans. is 5-speed manual. Tires are wider than the stock recommended size, but are the same diameter (I measured). shouldn't affect speedometer/engine speed ratio, anyway, just ground speed.

Cruising RPMs at 100 km/hour (what's that, about 62 MPH?) in overdrive is close to 2500 RPM. To me, this seems high for a big turbo diesel. I was expecting it closer to 2000... maybe 2200 tops.

Do these numbers match what's expected for 4:10 gear ratio? Or did someone put a slow rear end in there at some point (there's been a few owners). I may think about gearing it higher, but I need to know where I'm starting from first!

Thanks very much and thanks also for keeping up this forum. I learn tons every time I visit.

Scott

 

your gear ratio should have the engine spinning around 2093 (give or take a few). sounds like someone might have put lower gears in the rear. i used novak conversion's calculator and it looks like you might have close to a 5:1 gear ratio.

 

Sounds about normal for 4.10 gears.

I had 4.10's before and at 65 it was close to 2500rpm with 235/85-16's

I have 3.55 gears now and run just over 2100 at 65 now, with 285/75-16's

 

Sound right for 4.10's. Mine came that way but switched it out to 3.55 and I cruise at 1900rpm @ 75mph with an E4OD in overdrive.

 

I have 4.10s with a 5 speed and cruise at 70mph @ 23-2400 rpms. There was a thread on this the other day and many guys are the same. I'm at 2600 @ 75 and 2100 @ 65. These are estimated rpms but should be close. When I had the E4OD in they were a couple hundred or so lower in OD.

 

my 4.10s and E4OD have me at just around 2000 rpms at 60mph (33" tires)

 

I drive at 65 a lot, and its around 2200 RPM's with the same setup as the OP.

E4od has a taller overdrive than the 5 speed.
I have 33's for tires though also. Not sure if my speedo was calibrated. Last I checked it was still off.

Here is an easy way to figure out your rear end ratio.

Jack up the rear of the truck. (if you have an open diff, I think you have to leave one tire on the ground.)
Be sure to block the front tires, and put the truck in neutral.

Put a mark on the tire, and a mark on the driveshaft.
Spin the tire slowly, and count the amount of times the drive shaft mark goes around.

So, if you do have 5's in there, it will spin 5 times, and 4 times for 4, and with 3.55's it should be on the opposite side of the clock from where you made the mark originally.

 

Holy crap. I had no idea people spin diesel engines so fast!!! I got my first powerstoke not long ago, and I have a cow it spinning 1900 going 55mph. I guess I am used to big trucks, with 1800 ceiling rpm. When the thing shifts at 2400, i always cringe.

While on topic, kind of, do all of these truck tuners that adjust shift RPM just adjust for full throttle shift points, or do they lower part throttle shift points as well, also I would like the ability to lock out the downshift from over drive to 4th (E4OD) over 45 MPH (I tow a lot), unless I manually (shift lever button) call for a downshift. Is this possible??

 

Yea. Look at where the redline is on our trucks.

Cring when you see a dodge or a chevy hitting 2600 trying to keep up with us. =)

 

Well, I consider red line to be never approached. Low end torque is what a diesel is for. But I grew up with tractors, and driving semi trucks. First V-8 diesel. Never will like revving them out. Still interested in adjusting shift points.

 

3 grand is about the normal high end of the rpm band for our trucks. You can go over it, but its not necessary.
I rarely shift over 3 grand.

You don't start making any power till around 1800 rpms.

 

Doesn't that kind of engine speed dramatically reduce the life of these engines?, gotta be hard on it.

 

not really, there are several cases of 1,000,000+ 7.3s
and don't worry about the rpms, better to have lots of rpms and high hp then no rpm and lots of torque... torque doesn't do anything except add hp at the bottom of your rpm band, get out of the torque thinking

 

torque is applied pressure.the force power.
this is everything when it comes to moving a load.
this is why diesels outperform their gas equivalent when it comes time for work, because diesels have so much torque or "grunt" if you will.

think of HP as your momentum to keep the load moving,but its not the "force" / "grunt" that moves the load,thats the torque.when it comes to a "work" truck.torque means everything.HP keeps it moving along down the road.

 

Hey, Brutl_Force

When your pulling with these trucks you dont want to lug a load up hill at 1500 rpm. that will sky rocket EGT even on a stock truck. I'm not saying to redline it, just don't lug it. these trucks are most efficient between 1800-2400 rpm. this is where you get the most bang for your buck power and efficiency wise. I do know what you are talking about though about excessive downshifting !! that's why I went to the 5 speed manual.