Trying to help a friend that lives near Feets in Irving. He has a 2500 Ramvan with the 3.9(?) Claims it nedds another gear as it gets 400mi on a tank around town, and only 300 on the highway. He thinks it isn't an OD. When he first got it it didn't kick down. It does now. Fluid looks new according to a mechanic.

What tranny would it have? If non OD what OD should he look for?

What year?

3.9 2500 sounds wrong. Maybe 5.2 or 5.9...

It's an '02 Ramvan. I am guessing it is the 3.9 chopped off 318. It's a Magnum. I saw the V6 emblems on it when he came by for a visit.

So if he wanted to go OD?

BTW thanks for the responses!

od not worth it, its got the aerodynamics of a broken brick. In od that poor 3.9 will be really chugging especially with the highway gears in the rear. those vans are dine a dozen, get one with a 5.2 or 5.9

The purpose of OD is to get the MAP pressure up,
and to a lesser extent to reduce piston ring friction.

It is a bit hard to understand,
but the pressure of the atmosphere "wants"
to help push the piston down on the intake stroke
but if the throttle is too far closed
low pressure on the piston crown
will cause the other cylinders on power strokes
to "waste" some of their available power
to force the intake stroke piston down.

Have your friend hook up a vacuum gauge to his V6.
Drive on a fairly level interstate highway at his typical speed in 3rd gear, 1:1 ratio.

If his vacuum averages 8 inches of Hg or less
OD will not improve fuel economy much
especially the ratio 0.69 like a 46RE

He could "fine tune" his highway ratio
by going to taller tires,
especially new low rolling resistance narrow ones.

Since it is a van, consider aero tweaks to improve highway MPG. With enough aero improvements his cruising MAP will decrease to the point that maybe OD would become worthwhile.

Another trick is to lean the air fuel ratio somehow,
which will increase MAP too.

EGR will also increase MAP,
but anything over 10%
will begin to create spark missfires more than leaning with air will.

And from real-life experience.

My '64Dog came with 3.91s. When I put the big tires on it, it would average around 15 mpg on trips, with the stock 2-barrel carb.
Then I switched to 3.23s and expected a big mpg increase. However, mileage was exactly the same although rpm was down significantly. Noise was down, so it was easier to drive.

That engine is too small for the van and there's nothing to be done, except possibly turbocharging, to improve it.

R.

I am thinking the 3.9 is working hard. A 5.2 would probably be the same or better with the MPGs.

Thanks again! I suggested flipping the wires on the O2 sensors before and after the cat ala Hotroddave.

A 2500 with a 3.9 ? Thats really not enough eng for that van and it you load it down it will really strain. If its the 3 speed it should be a 32RE I believe as most of the rear drives went to electronic gov in 96 from what I remember. Course is should have the lock-up converter to help milage some. Does the van carry a heavy load alot ? Ron

There is a friend's '81 B100 in my driveway with 3:55's, 833OD and a 225 with a Rug_Trucker rebuilt BBD and Rug_Trucker work truck ported/polished head. But I digress......

My friends van with the 3.9 was bought with the idea of doing expediting. It hasn't been put to work yet. AFA 3.9's in vans? I have seen them in 3/4ton Maxivans!