Hi, I just acquired an 89 F-350 dually crew cab with 7.3 IDI, hypermax turbo, 5 spd manual tranny. I do not know what rear end it has, I could not find a data plate, and the VIN# check did not have a code for the rear end.

Running empty on the freeway I can hit about 70mph with the petal on the floor, and about 2700 RPM.

Pulling a 9,500 lb trailer I can hit 60mph on the flats with the petal down, but any type of incline I need to push down hard and fully engage the turbo to about 1000-1100 degrees. Typically it will run at about 2500 RPM (5th gear) 55 mph with the load.

Are these normal speeds and RPMs? Are there any tweaks or cheap/easy modifications I could make to get better performance, or should I sit back, relax, and enjoy the slower pace of life?

Thanks.

 

[quote=89BlackBeauty;6039818]Pulling a 9,500 lb trailer I can hit 60mph on the flats with the petal down, but any type of incline I need to push down hard and fully engage the turbo to about 1000-1100 degrees. Typically it will run at about 2500 RPM (5th gear) 55 mph with the load.
quote]

1000-1100 degrees, by this do you mean exhaust gas temp?

 

Yes, the turbo has a gauge in the cab with exhaust temp (I am not sure where it is measured from) and pressure.

 

89BlackBeauty,
Welcome to FTE and the IDI diesel forum.

Your numbers don't add up.

2700 RPM with a ZF 5 and 235/85-16 tires would run 74 MPH with 4.56 gears.
Same everything at 2500 RPM would be going 68 MPH.

The most common ratios were 4.10 and 3.55.

With 4.10 gears at 2500 RPM you should be going 76 MPH.
And at 2700 RPM you should be going 82 MPH.

What don't add up is a 15 MPH speed difference with a 200 RPM change.

Also you need to locate the thermocouple, 1100 degrees with a thermocouple after the turbo would be 1400 degrees at the pistons.
They start to melt at 1250.

 

I checked the RPM and the speed (stopwatch and mileage markers). 69mph at about 2750 rpm. 65 mph at about 2500 and 60 at about 2250. The exhaust temp is measured before the turbo hits the piston. It gets up to around 1100 and maybe 7 psi going up hill with the pedal down 70mph and gaining (not towing).
Do these numbers make more sense? I could hit 75 if I was pushing it.

 

Still looks like 4.56 gears.

2750 works out to 73 MPH though.
2700 works out to 71.8 MPH.

Does your truck have a regular pickup box or a flatbed on the back?

Might find gears like that in a cab and chassis rig.

See if there is a sticker on the drivers side door post, should be below the latch.
There should be an axle code listed on it.

Also very possible someone has changed the gears in the axle.