Gear ratio/type gear needed

[BigBK5]

I have read buttloads of threads in the search section,and narrowed it down to 4.56 gears(74 k5,300hp crate 350,th350,203 tc ,12bolt,d44,3.73 gears ,35in toyos) Want to tow my 20ft ski boat in the summer,wont see much freeway action. My main question is my carriers,truck had 308 gears at one time,so I assume I have the 373 and higher carrier? Do I need special gears for this carrier? And do you all agree on the 4.56 ratio? Seems sluggish to me with the 373,but my other truck has a procharged 454 with 373 and 32 in tall drag radials,so that's not a apples to apples comparison,lol.

 

[b454rat]

I believe have to get thick gears. 35s with 3.73s might be good for the highway, but not for towing. I'd think do alot better with the 4.56s. Call Randy's ring n pinion, they can tell you what to use .

 

[Ned Kelly]

I think 4.56 would be good. My friend had his K20 with 350/th400/205/4.56 and running 36" Swampers. Seemed like a good combo and he ran it like that for years.

 

[Wes Harden]

yes 4.56 and 35" tires will put at close rpm as 3.73 and 30" tires(stock) so at 55 you will be @2400 rpm with 4.56 and 35"

 

[Ned Kelly]

Like Wes states, use factory gearing as an example of what rpm range to strive for.
Consider that many square body 3/4 and 1ton trucks came factory with 4.11 and 4.56 gears, TH400, and only running 235/85R16 tires which have a diameter of 31.7.

 

[Wes Harden]

Hmm what speed does that chart represent?

 

[jeff in co]

I've towed my 94' MC 205 with the blazer with 4.10's and 35's. Not winning any races and is OK, but I'd probably lean towards 4.56 gears if possible, too.

 

[ZooMad75]

Like Wes states, use factory gearing as an example of what rpm range to strive for.
Consider that many square body 3/4 and 1ton trucks came factory with 4.11 and 4.56 gears, TH400, and only running 235/85R16 tires which have a diameter of 31.7.

View attachment 361202

Looks like the chart is for rpm at 65mph with 1:1 trans ratio. No od factored in.

I just plugged in the details into my Tremec gear calculator app. 4.1 axle, 35" tires in direct drive came in at 2,566 rpm.

 

[Ned Kelly]

Yeah, no od factored on that old school chart.
Also, need to consider torque convertor slip in 3rd and actual tire diameter (vs advertised diameter).

 

[Chevy350Ben]

Here is a helpful link I used when selecting gear ratio for my blazer on tons with 40s.

http://www.grimmjeeper.com/gears.html

I went with 5.38. But my truck will see very little freeway time, so I was happy sacrificing top speed for low end grunt.