I'm going to agree with Orich partly. Be sure of what your final gear ratios will be and make sure that it will keep the engine in its power band at cruising speed.

When I put my AOD in I had 3.25 gears and that was just too tall. I couldn't drive fast enough. I swapped to 4.11s and it is great.

 

Orich
I agree on your premise but you got this truck AND the GV two speed automatic OD all wrong.
There is NO WAY I'd lose mileage.
Check the device out and see.

It will effectively make my '67 into a 6 speed automatic. It is fully automatic so I get 6 forward gears.
I can with the click of a switch override the OD and go right back to a 3 speed.

I have 3.73 gears now so unlike your scenario...at highway speeds this combination would make 3.73s cruise like 2.91s
This truck has already proven it's towing capabilities. I made a run over California's famed "Grape Vine" while towing a small pickup. It was in cruise control, never down shifted and never dropped blow 9" of vacuum. (C-6 and 465 CID Cobra).

In Automode I'll have a much faster truck too as the trans goes first to first over, second to second over , third to 3rd over. Closer multiplier and stouter accelleration. This motor is done at 5200 and it is topped out before the quarter so I'll see much better quarter times too. I hope it pulls all the way after the upgrade.


If I want to select exact increased performance I can set the dash-switch to manual. This allows you to turn the overdrive on/off at any moment.

I will have one if I can keep it.

Bill

P.S. Those 3.25's (with the GV) would have a ridiculous OD final of 2.50's. I'm not sure what your OD calculates too.

 

As long as you can keep your vacuum up in good range then yea.
I know those spilt the gear ratios to get the best gearing at any speed with the o/d & gear-v.

But to me the o/d is a waste of $ with having a Gear -v while it does it all Right?
If it was a diesel with low power rpm TQ there would be no end to your high highway gearing speeds.
Orich

 

Gear Vendors OD is what I'd like to have with my '68 F250 with a 460, C6 and 3.73s. I'm sure I could get over 10 with the OD. I drive 60 and have a light, smooth right foot. When I had a 12' camper on it the mileage was just about the same. Just can't afford over $3000 for something I drive once a week if that.

 

I found a used GV unit that was setup for a c6 and found out that many guys who are selling them say just trade the adapter for the one that fits your tranny. They remove them from their truck before they selling there vehicle figure they'll get more by selling the GV out right.

I called GV IN So. Cal and they informed me that in no way they would give me any credit on the C6 adapter and they wanted it back for free. Plus no reduced in their sales price for the one , I needed since I had a 4 spd manual.
I say oh really, why he said they did not want any one to copying it or using it on another unit like Doug Nash units.

Plus this guy was not very polite in saying they must have it back.

I quickly made up my mine not to deal with these people.

I then researched the dodge nv4500 5spd and went that way which was about half the cost of a GV unit.
Orich

 

I think you're confusing the operation of it. I too had looked into buying one before I decided to do an AOD. From what I understood, it only engages after 3rd gear in auto. Manual mode you can kick it in and out.

Anyway, my AOD has an overdrive ratio of .67. So my 4.11s get cut down to 2.75s. Which is almost perfect for cruising yet not bog it out. I can even tow my trailer uphill in OD. (Provided it's not too steep )

 

That's exactly what I get with the same truck and engine combo.
I have a 3.00 rear that I want to install to get better highway speed and mileage.
Some day I might actually install the damn thing

 

Spent this Tank towing my 3000 pound flatbed trailer around loaded with various items.

Average 13.6!!!

 

15.3 again. Seems like that's a pretty solid best average for me.

I just did a little more "tuning" so we'll see what I do now.

 

34.2 MPG left Pebbles at home and Drove My Kia ..lol

 

I've had a few 302s, and all with 3.50 gears. My tired 72 shortbed 302 auto would average about 15 driving it 25 miles to work and back. EFI ones got 16-17 on long trips, 19.5 once with a good tail wind. With a light foot you sure shouldn't have any trouble getting into the teens unless your drive to work is metro and a lot of stop and go.
While there are those who will disagree, the taller gears really won't make much difference in mileage, it doesn't necessarily change the efficiency of an engine, just less wear and tear.
There is more math and theory than most of us can comprehend when we start bringing all the factors that affect fuel economy into play. Even exact same engines can have different personalitys due to core shift in the runners when they cast the heads or excessive casting flash. Every engine is going to have it's sweet spot. A vacuum gauge has already been mentioned. If you install one and drive with it at it's highest reading, you will be doing all you can for your set up. Also a tach is a good tool. With a stock cam, I like my highway cruise to be around 2000 rpm. .

 

Everyone of us can get better gas mileage when we drive in a fashion that we don't normally dive. Now when gas prices go up close to recored highs we is when we only slow down an stay in the slower flow of traffic.

We try not to don't waste gas by long engine warmups and shut the engine off if were waiting in some sort of line like waiting to buy gas.

Other wise for the norm we don't think about smart gas saving ideas.

Also getting older an slowly get wiser seems to add to getting better gas mileage too as we try to be more careful for the most part of the way we all drive.

And giving yourself enough time to get from point A to point B does matter when it comes to getting gas mileage.

Now by having a big gas pig horse power engine don't really belong on the streets today. It can get you into more troubles then you can ever imagine by driving stupid.
Drag racing an driving to fast for the road or weather conditions in heavy populated areas could end all your fun in a hurry if we hit & killed someone, so drive smart.

Orich

 

It has been a long time since I've had my 71 f100 302 2v 3 speed on the road. I always tracked fuel economy, I still do. Driving country roads 35 to 50 MPH always around 17 MPG. On my newer vehicles what I have found is driving habits have a big play in mileage. Example, my 2005 f150 5.4 I get consistent 17 MPG, if my wife drives it she gets 12 MPG. I have noticed that the wear on brake lining is also something that seems to correspond to driving habits. My brakes seem to last 6 to 7 years, my wife's brakes last 2 to 3 years. I am beginning to think she attended the Petty school of driving.

 

Your wife sounds like my ex-wife. She drove in two speeds. Heavy on the gas and heavy on the brakes.

 

Figure A...