Gearing questions???

[BroncoinAlaska]

Looking for some information / opinion on re-gearing from 3.50 to 4.10's.
1977 Bronco Ranger Uncut
Tire size: 235/75/15 Stock Hubcaps
Stock 302 2 barrel with C4 Automatic
90%Pavement / 10% Off Road

The Bronco is my daily driver and weekend warrior. I will keep the Ranger stock looking even after my upgrade to EFI later on this summer. I will be swaping in a mustang HO crate motor this summer and an AOD/4R70W over the winter or next summer. The build will be in stages, so I can keep driving and enjoying it.

The questions that I have are what are the dissadvantages of the change to 4.10?
Will I loose a-lot of top speed?
Will I still be able to drive 75?
What would be the expected RPM's @ 75?

 

[Phoenix0783]

mph = (rpm x tire diameter)/(Gear ratio x 336) so, rpm = (mph x gear ratio x 336)/tire diameter. (75*4.1*.7*336)/(235/25.4*.75*2+15)=2504RPM

 

[broncnaz]

While you could drive 75 with 4.11's and 29in(28.8 max) tires you would be pushing about 3700 rpm doing it. Once the OD tranny is in you would be fine with the rpm's down to about 2500 at 75.
I'd probably do axle gearing last. if at all. Unless larger tires are in your future. As even with 3.50 gears currently you run about 3100 rpm's at 75 with a AOD you would run about 2100 rpms. You may want to consider other gearing such as 3.73's or 3.93's

 

[Viperwolf1]

mph = (rpm x tire diameter)/(Gear ratio x 336) so, rpm = (mph x gear ratio x 336)/tire diameter. (75*4.1*.7*336)/(235/25.4*.75*2+15)=2504RPM

Should be closer to 3600 rpm w/4.10s.

Nevermind, I didn't figure in the OD.

 

[Flintknapper]

mph = (rpm x tire diameter)/(Gear ratio x 336) so, rpm = (mph x gear ratio x 336)/tire diameter. (75*4.1*.7*336)/(235/25.4*.75*2+15)=2504RPM

Unless I missed something...he will be well over 3,500 rpm at 75 mph with a 29" tire? (1 to 1 no overdrive)

Unless he plans on running a taller tire later on....I wouldn't bother re-gearing since he is going to be putting in a more powerful engine.

Chances are, (off road) he will be in low range a good amount of the time, so he wouldn't really need the 4.11's

I wouldn't go over 3.73's if it were me (90 % on road and small tires), if I re-geared at all.

The AOD would make a nice addition for the overdrive at which time your calculation would be roughly correct.