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I have a 1983 Ford f150 with a c6 transmission. I’m wondering if there is a way to get more speed with less rpm’s? Topping the truck out at 65 mph just seems a little slow when everybody is passing me going 70. I’m pretty sure the gearing in the rear diff is 3.5. I thought about putting a gear vendor in but that seems like its gonna put my transfer case in the bed.
engine is 300 i6, gear ratios is 3.5 and the tire size are 15’s pretty sure.
Most compact efficient way to get overdrive is to get a later model overdrive transmission. It's still not cheap, but the cheapest way is to get a 88-96 used truck with overdrive, either running or wrecked, and get the overdrive transmission out of it. You will get all the pieces you need to install the transmission, and you will have lots of extras to sell off to recoup your money. You could even put your c6 in the newer truck and then resell the whole thing. You will need to buy a controller, but it will give you some neat features the newer trucks have, like tow-haul and different modes of shifting.
engine is 300 i6, gear ratios is 3.5 and the tire size are 15’s pretty sure.
Would be nice if we had the full tire size as 15 can be 27" tall to 40" tall and that can change the RPM a lot. To add the C6 auto and I picked up it is a 4x4 from "transfer case in the bed" line, it is now all in 1 place.
What is the RPM at 65 MPH? Will it go faster if you tried and just dont feel it is safe for the motor?
I ran the numbers and at 75 MPH is little over 3000 RPM 62 MPH is 2500 RPM so 70 MPH is somewhere between the 2 RPM's
I used a 29" tall tire in the math.
There are 2 ways you can go to lower the RPM, well 3 ways really.
I hinted at 1 with tire size. A taller tire will lower the RPM but also make it a dog from a stop when taking off.
#2 would be a gear ratio change x2 because you have a 4x4. Going from a 3.50 to a 3,08 or lower, you are limited by ratios you can get for both front & rear axles.
Just like taller tires a lower number ratio gear will also do the same taking off from a stop and being a dog.
And with tires & gears besides being a dog from a stop if you have a load in the bed or pull a trailer the truck will be a bigger dog than just from a stop.
#3 you hinted this one, Gear Vender over drive. Now unless they went and changed something in the last 5 years it dose not fit between the rear of the transmission on 4x4's, it gets installed on the back of the transfer case and ONLY to the rear axle. READ CAN NOT BE USED IN 4X4 MODE!
What is nice (in my book) is you can split the gears so the 3sp C6 is now a 6sp C6 so if you find 3rd is too high a gear and 2nd to low split 2nd and run 2nd over drive.
If in 3rd over drive and hit a hill with a load you can just go to 3rd direct and motor on.
Now if you look into the Gear Vender as say Holy Crap on the price look into the cost of changing gears front and rear between the parts and labor to do the job.
The GV you should be able to install it yourself over a weekend and the only other thing is getting the drive shaft shorten.
GV is the only add on over drive that I know of now days.
#4 OH I almost for got you can swap out the C6 for a over drive auto. There are others that know the OD autos so I will let them speak up but I think it could be as much as the GV set up.
Yes I looked into over drive for my 81 F100 with 300, NP435 (granny first 4sp) 2.75 rear gear and 235-75-15 tires.
At the time I went with Advance Adapters OD, no longer made, and it works great for when I use the truck for. My 4sp is now a 8sp as I can split all the gears.
In 4th direct 80 MPH is 2800 RPM in over drive 80 MPH is 2200 RPM
Dave ----
What is the RPM at 65 MPH? Will it go faster if you tried and just dont feel it is safe for the motor?
I drove the ‘87 Bronco (302/C6/3.55) all the time on the highway. That engine logged just shy of 300K miles before it spun a bearing. It didn’t seem to care about doing 3,000 rpm or more while keeping up with traffic.
I drove the ‘87 Bronco (302/C6/3.55) all the time on the highway. That engine logged just shy of 300K miles before it spun a bearing. It didn’t seem to care about doing 3,000 rpm or more while keeping up with traffic.
Thing is the 302 works / makes power in a higher RPM range than the 300 straight six.
The 300 makes it's power down around the 1800 to 2000 RPM area and mine will pull from 1000 RPM try that with a 302 motor.
In over drive mine is turning 1800 RPM @ 70 MPH the speed limit here. 80 MPH is only 2200 RPM
As they say the 300 will not win any races as it is slow but it gets the job done.
The 300 is a truck motor and used in larger than 350 trucks, the 302 not in anything over a 250.
Dave ----
Would be nice if we had the full tire size as 15 can be 27" tall to 40" tall and that can change the RPM a lot. To add the C6 auto and I picked up it is a 4x4 from "transfer case in the bed" line, it is now all in 1 place.
What is the RPM at 65 MPH? Will it go faster if you tried and just dont feel it is safe for the motor?
I ran the numbers and at 75 MPH is little over 3000 RPM 62 MPH is 2500 RPM so 70 MPH is somewhere between the 2 RPM's
I used a 29" tall tire in the math.
There are 2 ways you can go to lower the RPM, well 3 ways really.
I hinted at 1 with tire size. A taller tire will lower the RPM but also make it a dog from a stop when taking off.
#2 would be a gear ratio change x2 because you have a 4x4. Going from a 3.50 to a 3,08 or lower, you are limited by ratios you can get for both front & rear axles.
Just like taller tires a lower number ratio gear will also do the same taking off from a stop and being a dog.
And with tires & gears besides being a dog from a stop if you have a load in the bed or pull a trailer the truck will be a bigger dog than just from a stop.
#3 you hinted this one, Gear Vender over drive. Now unless they went and changed something in the last 5 years it dose not fit between the rear of the transmission on 4x4's, it gets installed on the back of the transfer case and ONLY to the rear axle. READ CAN NOT BE USED IN 4X4 MODE!
What is nice (in my book) is you can split the gears so the 3sp C6 is now a 6sp C6 so if you find 3rd is too high a gear and 2nd to low split 2nd and run 2nd over drive.
If in 3rd over drive and hit a hill with a load you can just go to 3rd direct and motor on.
Now if you look into the Gear Vender as say Holy Crap on the price look into the cost of changing gears front and rear between the parts and labor to do the job.
The GV you should be able to install it yourself over a weekend and the only other thing is getting the drive shaft shorten.
GV is the only add on over drive that I know of now days.
#4 OH I almost for got you can swap out the C6 for a over drive auto. There are others that know the OD autos so I will let them speak up but I think it could be as much as the GV set up.
Yes I looked into over drive for my 81 F100 with 300, NP435 (granny first 4sp) 2.75 rear gear and 235-75-15 tires.
At the time I went with Advance Adapters OD, no longer made, and it works great for when I use the truck for. My 4sp is now a 8sp as I can split all the gears.
In 4th direct 80 MPH is 2800 RPM in over drive 80 MPH is 2200 RPM
Dave ----
the truck will go up to 80 I haven’t pushed passed that but I don’t like pushing it like that lol she’s old and I can respect that I haven’t done anything to the engine other than timing.
so the gv mounts behind the transfer case? I may have so hope after all😭🫣 I’d honestly prefer to go with the gv is seems like the easiest route for me just an install and a new rear driveshaft from what I understand?
Just don’t use the gv in 4x4?
this may be a dumb question but is gear vendor the only company that actually makes the gear vendors or which would you recommend?
and unfortunately I don’t have a tac I’m about to buy one of those as well
A Gear Vendor bolts to the back of the TC, and requires a new driveshaft. They come with a lockout to prevent use when in 4x4. But you are looking at over $4,000 to buy one and install it yourself, $4500+ for them to do it.
And GV is the only game in town for this type of OD.
Back to your setup.
Your 265-75x15 tires are said to be 31 inches in diameter. So let's go 30 inches just to allow for inflation differences, tread wear, etc.
I wouldn't run 85 for very long, but 65 to70 won't hurt a thing. Gas mileage will never be good with this setup, and the faster you go, the more gas--you knew that.
So save you nickels and save your dimes.
For $4500 you can buy a lot of gas, and even blow up and replace a 300 once.....(used motor of course).
A Gear Vendor bolts to the back of the TC, and requires a new driveshaft. They come with a lockout to prevent use when in 4x4. But you are looking at over $4,000 to buy one and install it yourself, $4500+ for them to do it.
And GV is the only game in town for this type of OD.
Back to your setup.
Your 265-75x15 tires are said to be 31 inches in diameter. So let's go 30 inches just to allow for inflation differences, tread wear, etc.
I wouldn't run 85 for very long, but 65 to70 won't hurt a thing. Gas mileage will never be good with this setup, and the faster you go, the more gas--you knew that.
So save you nickels and save your dimes.
For $4500 you can buy a lot of gas, and even blow up and replace a 300 once.....(used motor of course).
Do you have a decent muffler?
I have the oem muffler for the truck supposedly, I got it off rock auto.
also what gear ratio should I get in the check out menu? When I rebuilt the rear differential it had 42 teeth on the ring gear and 12 on the pinion so 42/12=3.5 but the closest choice there is to that is 3.54?
and my last question is do any of yall recommend someone for the new rear drive shaft that I will need once installed?
I appreciate all the information yall have shared with me I know some of yall are prolly tired of answering the same question a 100x so thank you
also what gear ratio should I get in the check out menu? When I rebuilt the rear differential it had 42 teeth on the ring gear and 12 on the pinion so 42/12=3.5 but the closest choice there is to that is 3.54?
and my last question is do any of yall recommend someone for the new rear drive shaft that I will need once installed?
I appreciate all the information yall have shared with me I know some of yall are prolly tired of answering the same question a 100x so thank you
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