Engine RPM question

[sandawgk5]

I have 3.08 and 31s on 10 bolts I am in the process of chaning to Dana 60 and 14 bolt with 4.10s and I am trying to decide on tire size. With 31 and 3.08 I at 70 I am only turning about 1500 RPM. With the 4.10s I will be turning about 1795 with 35s and 1900 with 33s. I really want to go with 35s because when I do add a lift I will already have a decent size tire but is ~300 RPM enough to get the engine in the range where it is happy. I have a stock 350 TBI and 700R4 and I can not keep the tranny in OD in my current setup. I also have a tranny cooler in front of radiator as well as the cooler in the tank of the radiator. Also I have noticed there is only about $5-$10 difference between 33s and 35s. I dont want to regear now because I plan on going to 5.13s so I only want to do it once. Any opinions or advice welcome.

Thanks
Ira

 

[divorced]

Where do you get your numbers from?

With 33's, 4.10 gears, and over drive at 70 mph I get 2045.5 rpm.

And 1928 rpm with 35's.

Unless maybe I read your question wrong... then carry on and don't mind me.

 

[pauly383]

Your gonna regear later , then get the 35's anyway . With 4.10's and 35's it will be fine for now .

I run 33's with ONLY 3.73's , and in OD at 70 I almost see 2000 rpm . 35's and 4.10's will be simmilar . I really don't gear hunt , and I have way LESS motor than you .

You do want lower gearing later , I do too

 

[PhoenixZorn]

Sure wish I had OD... with my 465, I'm seeing 2450rpm at 65mph in 4th gear... which should mean I have 3.42s... I also have 31s and plan a 35 4.10 upgrade...

I was just thinking... that chart is for OD trannys, not a SM465... I'm thinking I still have 3.08 gears due to my higher than OD 1:1... isn't OD like .70:1?

 

[sandawgk5]

I got my numbers from the chart on samsoffroad I know those are just estimates. I was mainly asking because I want to actually be able to use overdrive on the highway and not have the tranny hunting all of the time but if it is around 2000 that is just about perfect then eh?

 

[89GMCSuburban]

OD depends on the transmission. 700r4 is .76:1 I believe. Your 4th gear is 1:1 the chart IS for yours because it does not take into account that not all automatics (older ones) don't lock up the converter. Thos RPM's shown are resultant of direct drive i.e. manual trans or auto with converter lockup.

 

[PhoenixZorn]

Ooo... so I DO have 3.42s...

 

[divorced]

Here is the best calculator I have found http://www.florida4x4.com/tech/gearcalc.php