Well im looking at an alternative overdrive option thing is its 0.78:1 vs the 0.67:1 AOD. Question that i have right now is how much of a improvement would i see acceleration wise with 3.55:1 gears compared to the 2.75:1 i have now?

Tires are taller 31x10.50-15 which are 30 1/2" tall. This is on my 82 F150 302/c6 combo.

My other question is for gear ratios you buy from like richmond for example, what tire heigth is the ratio calibrated for? Is there an industry standard that the gears use the same heigth tire? Trying to also figure up gear ratio change based off tire size difference to help in my selection.

 

If it will help, I have a 1983 302, AOD, 235/75/15 tires and a 3.55 rear end. I find acceleration to be fine. Fast? No, but i feel I'm ok off the line and can pass and merge safely.

 

3.55 would be a very noticeable difference compared to the 2.75.

There is no standard relation between tire size and gear ratio. Tire size plays a part in gear ratio, but it's up to you to select the tire size you want, and then the gear ratio you want to accomplish what you want the truck to do. I would not go over 31 inch tires, or rubbing problems can occur if you load the truck down.

 

Of course im not running any other size tire than this. Its just that im trying to find a happy medium for me between improving acceleration and highway cruising speed.

Right now i turn 2500 rpm at 70 mph. My goal is to improve that to 80
mph but if i cant do that with improved acceleration then ill settle for same speed i have now.

Based off axle ratio and od ratio im looking at 2.77:1 with 3.55:1 and 2.91:1 with 3.73:1. Cant seem to get 2.75:1 or higher unless i go with a 3.23:1 which i think will be a waste of money for doing this overdrive install and gear change.

 

What is your rpm goal for 75-80 mph? Just remember, the 302 doesn't have much oomph at lower rpms, and pushing one of these trucks(bricks) through the air at 80 takes a lot of hp.

You don't have overdrive right now correct? Even if you end up with the same rpm that you have now, your acceleration will be greatly improved with overdrive because the tranny will be shifting against 3.55 gears. Then in OD you will be back to the way you are now. During any passing maneuvers or hill pulling you will have to let the tranny get itself out of overdrive, and then you will see improvement. If you drive any newer vehicle it's always the same, you have to wait for it to downshift.

 

Ideally im shooting fo 70 to 80 to be at 2500 rpm. Right now i do 70 at 2500 would like to do 80 at 2500 but its not a set in stone make or break deal.

Im also not going to use a AOD like my original plan was. For me i can buy a c6 gear vendors electronic overdrive for less money than buying a good rebuilt AOD locally with the proper carb converter and flexplate.

So effectively ill have a 6 spd auto since it splits your gears and its safe to tow with the od engaged. Down side its a 0.78:1 od vs the 0.67:1 od for the AOD which would have allowed me to run up to a 4.10 gear. So now im going back and forth between a 3.55 and 3.73. Supposedly the 3.73 will have me a few hundred rpm higher now at the same speed while the 3.55 would have me right back where i am right now. Truck runs good like it is, just trying to spice it up imporve towing capability as well as better highway speeds.

 

I'd go with the 3.73 if you're going to tow at all.

 

You can go with a lower numbered gear if you are going to keep the c6. The c6 torque convertor is "loose" meaning it has some slip. So when the going gets tough up a hill, it will start slipping a little bit more, letting the engine rev giving you almost another virtual gear. But then again, that's why the newer trannies are better for fuel mileage with their lock-up converters. And it's also important to add a tranny cooler for any auto tranny that will be towing, that "slipping" causes heat.

I am surprised the numbers add up when comparing the overdrive unit to the automatic. You will have close to $3000 in the overdrive unit when done correct? Driveshaft work and all?

 

The overdrive unit is $3,000 by itself. Having a driveshaft made is going to be $200. The axle work ill do myself but the parts for the ring and pinion gear will be $271.17 and the truetrac 31 spline differential is $504.97

Local shops i called wanted $1,200 for a stock rebuild AOD. With a wider '93 od band upgrade and a tow shift kit will put the transmission around $1750 built. Then need a torque converter, flexplate, new carb the carb will be right at $300. Then the fun of locating the tv rod proper for the truck. Then locating a oe heavy duty trans cooler that splces between the radiator cooler and the transmission.

 

The universal lokar TV cable seems to get most people going with the AOD transmission. So you may be able to keep your old carb. You will need that cooler on both setups. Rebuild doesn't include a rebuilt torque convertor? I would check. They may need a core though.

 

I would certainly go with the AOD as long as you don't tow anything crazy. While you may end up with around a 2.75 ratio again in OD with the AOD, the engine will still turn a bit slower since the converter will lock up in 4th gear, unlike the C6, a full time slush box

 

EDIT: After some number checking, with a 3.70 rear ratio you'd be at ~1950 rpm at 70 and ~2200 at 80, which wouldn't be a very bad thing considering the 302 would have to overcome more wind resistance and would be sitting around its torque band