Okay I've always worked on cars and trucks. But never messed with any rear end. I am buying a 1987 f250 4spd with 4:10 gears in. It raps out at 65mph due to rear end and of course being a 4spd. What is the best gear ratio to get for this truck while still leaving plenty of power to pull/haul. Its going to be a welding rig. Don't want an automatic. Also does anyone know where I can find a good Turbo for the 6.9L diesel? I want a Turbo. Please help!!!!!

 

welcome to FTE.
turbos can be picked up on the internet usually for between $500 and $1000. the two popular units are the Banks sidewinder, and the ATS.
banks also has the older non waste gated sidewinder and the newer sidewinder with waste gate.
there is also the hypermax turbo , but they are not seen used very often.
with the 6.9 and 4 speed, you should see top speed of around 80 mph. it will take forever to get there, but it should it.
with your setup, going to a higher gear will render the truck a hazardous slug if you put any weight on it.

my 88 7.3 with C-6 trans and 4.10 gears tops out at 80 mph.

what size tires are on the truck? it sounds like it has larger than stock tires and the speedometer was not re calibrated.

 

The Sidewinder is $2996 when I found it. The tires are 275/75/16. They match the sticker on the truck that's inside the driver door. The transmission the guy said is some racing transmission. But in the truck going 65 its rapped at like 3,000rpm.

 

that price is for a new turbo kit.
if you look around on craigs list and ebay, used kits pop up all the time.

and if i remember correctly, the stock tire size on the F-250 was the 235/70/16