i still need just one more explanation, i have stock 3.50 gears in my 84 and i run 32's. im putting 35's on it soon and if i go to a 3.89 or 4.10 will it raise my rpm's from 2,000-2,100(55-60mph). i do not want to run much higher so any explanation would help. and its a 351w/c6

 

I have a similar set-up as your's, with the 351W H.O., C-6, 3.50 gears and 35" tires. While 4.56 is the ratio needed to get back to "stock", I haven't noticed much difference in RPM's at 60mph, although the speedo is now off (actually doing 72-73 at "60"). You can do the math with one of the many formulas for tire size, RPM's, etc. if you want.

 

si if i put 4.56 gears in it will it still run 2000 rpm's?

 

Yes, but at a different speed than before. My tach was at 2400rpm at 60mph with 32"tires. At the SAME RPM level with 35's, I'm actually going closer to 80mph. In other words, my tach is somewhat lower at 60mph now than before, about 1800rpm.

There's still plenty of "power" to get down the road, though. The difference is not that much, but would be noticeable if pulling a trailer or with an OD tranny.

 

Can someone figure out what gears I'm runnin in my 80 Bronco? 351m/C6 with 33 inch tires. My speedo is right on the dot, followed a friend in a 2000 escort. Goin 55 mph, im runnin pretty close to 2400 rpm, maybe 2350. I put the numbers into a conversion chart thing on another site and it said like 4.26's?? Dont think thats right...

 

The closest ratio is 4.10, which is right for 33's. Best way to be sure is look for the I.D. tag on either axle.

 

Its possible that someone regeared your rig to 4.3. That gear set does exist.

 

Try this link. it will help you with your calculations.
http://www.superford.org/garage/calculators/index.php