What HP/TQ is this detroit 12.7l? How to find out?

Being that old it could be set at who knows what.
Most shops can plug in a laptop and see exactly what you have. Less than $100, maybe even no charge. Best to know what you have.
Need it reprogrammed Diesel Control service is the best, you can learn a lot about a 12.7 by watching his videos.

 

If say 500HP on the data plate that should be how it come from Detroit. The owner must had it turned down would be my guess. You can have it turned back up real cheap or free. You probably won't even notice any difference because 30HP is nothing. It the torque that makes a big difference.

 

I must be missing out on the freebees out here, since when do shops give there services away. These same guys ##### about cheap freight but want someone else to give there service away. You should have gotten an ECM download before you bought the truck but now that you own it I would get one just to check out whats going on in general with the truck.

 

Not much saved info in that ecm, but you can see all the settings, I didn’t say ask for free but it takes 5 minutes and they may not charge, my 99 does not have the factory ecm and is not set anywhere near factory, you need to know, if factory tag says 500 then you probably the good pistons and cooling nozzles

 

It’s a 500 hp just as tag says. I doubt it’s been turned down. From what I understand the old 470hp, known for better fuel economy have different injectors than the later 500 hp. Plugging it in will tell for sure, also you’ll be able to set perimeters for cruise, Jakes on cruise, minimum cruise speed and other things. There should be a 800 phone# for Detroit also on valve cover. They’ll tell you everything you need to know.

 

Later 500 hp were 1,650 ft-lb torque.

 

This is what Kenworth shows:

 

I had a 1998 430/500 hp.
I only got 500 on cruise, but it's a farce anyway as you didn't get that until 2100 rpm and I never went over 1700 rpm