Trans, Tires gear ratio help

[mikeiam82]

Hi, i recently purchased a 1969 bronco with a 68 body and im looking for help in the gear ratio transmission and tire combinations. Im currently planning on swapping in a 89-93 302EFI/NV3550/Dana20 combo for the main drive train. I believe the bronco has 3.50 gears but theres no tag and the wheel turn test has been inconclusive (2 turns of the tire turns the driveshaft 2 and a bit). I was using the gear ratio calculator on grimmjeeper to determine what would work best and i was thinking of using either 3.70 or 4.11 with 33's.

So to sum it up 302efi/NV3550/dana20/3.70 or 4.11 /33's. This is going to be used as a 80% highway and 20% off road and i was wondering if there was anyone here with any experience with this setup or 1 similar that could tell me how this works. This setup would allow me to run at these speeds:

50kph 2nd- 2700 rpms

3rd- 1650 rpms

80kph 3rd- 2600 rpms These specs are with the setup and 3.70 gear ratios.

4rth-1899 rpms

110hph-4rth- 2611 rpms

5th- 1906 rpms

Theoretically to me this setup would make the best for passing power/cruising for optimum mpg for the road.

Any opinions/criticisms/and words of encouragement are greatly appreciated.

 

[Bully Bob]

Hi Mike.!

Looks like you're way ahead of most of us. And., you've done your homework. :-B

All I can add is the lift (body/suspension) is involved in tire size., along with fender-wells.

As I recall., "Posi" req. both wheels off the ground for ratio test. Open dif. req. one wheel on the ground to get correct count.

Chalk mark the floor & bottom of tire. Chalk mark the dr. shaft.

One rotation of the wheel should give you 3 1/2 rotations (350's) of the dr. shaft.

4+ a little = 411's & so on.

I'm guessing you have 411's

Do fill-in your sig. & keep us posted...pics as well..?? >< <'>

 

[mikeiam82]

Hi Mike.!

Looks like you're way ahead of most of us. And., you've done your homework. :-B

All I can add is the lift (body/suspension) is involved in tire size., along with fender-wells.

As I recall., "Posi" req. both wheels off the ground for ratio test. Open dif. req. one wheel on the ground to get correct count.

Chalk mark the floor & bottom of tire. Chalk mark the dr. shaft.

One rotation of the wheel should give you 3 1/2 rotations (350's) of the dr. shaft.

4+ a little = 411's & so on.

I'm guessing you have 411's

Do fill-in your sig. & keep us posted...pics as well..?? >< <'>

the tire rotation test was the same with both wheels lifted and 1 on the ground, ill be yanking it apart soon and ill count teeth to be sure. 2.5inch suspension and a 1 inch bodylift are also planned. I posted some pics but im not sure where they went <_<

I cant wait to get into it, ive been working on cars and trucks for 20+ years and been a bodyman for 11 years. I know you dont start nothing without researching first

 

[Hatu]

Hi, i recently purchased a 1969 bronco with a 68 body and im looking for help in the gear ratio transmission and tire combinations. Im currently planning on swapping in a 89-93 302EFI/NV3550/Dana20 combo for the main drive train. I believe the bronco has 3.50 gears but theres no tag and the wheel turn test has been inconclusive (2 turns of the tire turns the driveshaft 2 and a bit). I was using the gear ratio calculator on grimmjeeper to determine what would work best and i was thinking of using either 3.70 or 4.11 with 33's.

So to sum it up 302efi/NV3550/dana20/3.70 or 4.11 /33's. This is going to be used as a 80% highway and 20% off road and i was wondering if there was anyone here with any experience with this setup or 1 similar that could tell me how this works. This setup would allow me to run at these speeds:

50kph 2nd- 2700 rpms

3rd- 1650 rpms

80kph 3rd- 2600 rpms These specs are with the setup and 3.70 gear ratios.

4rth-1899 rpms

110hph-4rth- 2611 rpms

5th- 1906 rpms

Theoretically to me this setup would make the best for passing power/cruising for optimum mpg for the road.

Any opinions/criticisms/and words of encouragement are greatly appreciated.

I put a NV3550 in my 69 Bronco with a 302 and did the math to figure the right rear end ratio.

With the three speed standard trans a 3.50 rear and 32" tires you get the following: At 3000 RPM you would get 81.59 MPH.

With the NV3550 and it's .78 OD 5th gear, you need a 4.56 rear gear to get close to the same RPM and MPH; with the 4.56 and 3000 RPM you would get 80.3 MPH.

I'm changing my rear and front axle to 4.56, should be great for crawling as well as the sand!

 

[mikeiam82]

I put a NV3550 in my 69 Bronco with a 302 and did the math to figure the right rear end ratio.

With the three speed standard trans a 3.50 rear and 32" tires you get the following: At 3000 RPM you would get 81.59 MPH.

With the NV3550 and it's .78 OD 5th gear, you need a 4.56 rear gear to get close to the same RPM and MPH; with the 4.56 and 3000 RPM you would get 80.3 MPH.

I'm changing my rear and front axle to 4.56, should be great for crawling as well as the sand!

Thanks for the info

 

[mikeiam82]

I put a NV3550 in my 69 Bronco with a 302 and did the math to figure the right rear end ratio.

With the three speed standard trans a 3.50 rear and 32" tires you get the following: At 3000 RPM you would get 81.59 MPH.

With the NV3550 and it's .78 OD 5th gear, you need a 4.56 rear gear to get close to the same RPM and MPH; with the 4.56 and 3000 RPM you would get 80.3 MPH.

I'm changing my rear and front axle to 4.56, should be great for crawling as well as the sand!

I was just running over these number again and i totally understand what you are saying, with your setup up you run 4.56 for low end torque and power for the dunes. At the 3 speeds of 30-50-65 mph you would be running at 1900-2300-2200 rpms so highway speeds would be achievable without screaming down the road. I on the other hand am building a DD for the road and mainly summer driving ( up here in Kelowna B.C. summers are like Californian and winters are like Alaskan ) so by running 4.11 ill be bringing the rpms down to 1750-2000-1950 at 30-50-65 mph and buy running 3.89 it will come down to 1650-1950-1850 at 30-50-65. I know these are the U.S.A.'s main speed limits and these translated over to kph are 50-80-110 which are our main speed limits so it should work out great.

I value the info you've provided, its helped me visualize how the bronco will actually respond without actually testing and spending money figuring out whats best. I figure by upgrading the engine and transmission from stock expecting better performance than stock should result. Judging by this I will probably run the 4.11's being as thats what is most likely in the bronco and if i have to upgrade to 4.56 it will be a minimal cost.