Currently in an F150 but looking to move up to a 250. As I did the build and price on Ford's website, I couldn't get the 4.3 gears with the Diesel engine... Only the gas engine. Can anyone explain why?

 

Take a look at the torque vs RPM curves of a gas engine and a diesel engine and you'll have your answer.

- Jack

 

Ok, did that. My take on that is the diesel doesn't need the higher gears since the torque is higher to start and pretty much stays constant while the gas engine starts lower on the torque so it would need higher gearing. Yes?

 

Also, the redline on the diesel is a lot lower than the gas engine.

 

Correct, and to add to glc's post, the 4.3 gears would have your RPMs too high at all times. It would seriously limit your top speed with a diesel.

- Jack

 

X2 on both of these being the reason. If you get a 6.7, even 3.08 gears would be sufficient haha. So 3.73s, or 4.10s, or whatever they come with will be more than enough.