What engine would you use if this was you?

My family bought a brand new ‘99 fl60 24ft single axle with a 230hp 3126b cat and a 6 -speed spicer. As has been said above the 5.9 cummins was only one offered other than the cat. If i remember correctly they offered up to 215 hp on the cummins I think. I have over a million miles on the truck and it was grossing everyday at 33,000. Its still strong. Retired it in 2015 just use it now and then.
Turn the hp up change tranny and driveline to handle the extra power and go.
Running above 33,000 on a single axle is pushing it ( tire and spring capacity ) in my opinion. But legally you dont need tandem till 54,000.
If you go bigger/ heavier engine you will have to “beef” up steering axle springs anyway.

 

When we speced that truck in ‘99 I do believe that the 8.3 was available in the FL70 and higher Business Class.
We bought another FL 60 identical in ‘03 with 3126e 250hp cat and at that time they offered the 8.3 240 hp Cummins and the “new” Mercedes.

 

The 12v cummins is actually rated for 66,000 lbs gross back when they came out.

For power and cooling the factory hx35 turbo is the limiting factor.

I have changed my compressor wheel on my hx35 to a higher efficiency wheel which actually lowered the coolant temp, exhaust temp and much more responsive.

With 50 hp DDP injectors, gained 3 mpg while towing over factory setup.

Made 390 hp with about 1,300 tq at the wheels.

Sure feels like I’m driving a big truck with frame and driveline twisting in my Dodge while pulling a load.

 

I would jump on that truck if it is as clean as you say it is and super low mileage too.
Even with only 240 hp ours has been a great truck and pound for pound it worked its booty off and got the job done with hardly any complaints.
It did the same work as our big boys just in smaller doses.
That’s how I got the “Small Package” handle from the old timers in the family. Lol!
Get it. Use it. Modify it how you need to to make it work for you.
If you don’t grab it it will probably end up down in ol’ Mex.
sad.

 

Btw at full 33,000 gross pushing wind it would run 75 at 2400 rpm in top gear all day long. Kept up with fast flow of traffic really well. South and central hill country Texas terrain. Never pulled any grades steeper than around Kerrville Tx. on I-10 so I don't know how it wouda done in that situation. Has 3.90 rear and would average 7.1 to 7.25 mpg.

 

Best engine ever made..DD60

Modern engine?? 12.7litre probably. I have DD13 no problems. Yet..haha

 

Our ‘99 is around 15,000 with 24ft 96 wide Supreme mfg. box not sure box height but whole truck is at 12’-9” tall ground to top. Has double frame from cab back and maxon fold away 2500lb. Lift gate.
The ‘03 is 12,000 same spec but we noticed a lot more aluminum components that are steel in the ‘99

 

Sorry forgot. The boxes (body's) are both aluminum sides and roof. NOT FRP. They have fully lined ply wood walls inside and wood floors. Pretty heavy spec. And lift gates are steel not aluminun.
Hope that helps.