I tried to search this topic before asking but i couldn't find any answers to this question:

Why did Ford put a 3.9L engine in the 2004 v6'ers?

Just curious, thanks!

 

i dont think they gave a real reason, my best guess is that the 2004 is the 40th anniversary mustang and they wanted to do something for the v6ers it has the same hp, same torque, all the 3.8 parts work on the 3.9, they just changed the crank and the pistons slightly

 

The reason is the "ALL NEW" Freestar minivan in 2004. The Windstar and 3.8L engines had many problems associated with them and Ford wanted this new van as separated from the old van (& engine) as possible.

By increasing the 3.8L stroke by 0.074", the 3.9L engine was born. The Freestar's optional 4.2L engine is again a stroked 3.8L (0.35" more stroke). Basically the only parts that differ between these 3 engines are the crankshaft & pistons.

The 2004 V6 Mustang started up the production year with 3.8L engines (until they were gone I'm guessing) and switched over to the 3.9L sometime before the end of the 2004 (Oct~Dec).

Anyway, the 3.9L was more or less a marketing gimmick to help sell the new Freestar.

I however can't see how producing just 3.9L engines instead of both 3.8L & 3.9L for a 1/2 year could have been cheaper than the cost of emission certification for a 1/2 model year of 3.9L Mustangs. Obviously Ford's been counters though otherwise !!