Chevy six RPM

[Ohio Blue Tip]

Still working on my 1952 chevy truck, ya I'm slow (and old).
Running a 1954 235 six with dual W-1 Carter carbs and split exhaust.  Using an S10 5 speed trans and ford 9" rear.
Need to add a posi and a gear change.
At highway cruising speed , 75 MPH all day.
What RPM should I shoot for ??

[kb426]

I'm a long ways from a 6 expert but I can tell you what I've done and the results. The 32 has a 3.50 rear, a .68 overdrive and a 29" tall tire. I run 1750 at 70 mph. The t5 has a .63 overdrive I believe. If you need help with a ratio calculator I can find several good ones on the internet. I would think you could run that engine between 1400 and 1700 and be real good.

[chimp koose]

don't know if this helps but the ford 300 6cyl makes max torque between 1600 to 1800 rpm if I remember . I would think that 235 might do the same ?

[enjenjo]

A S10 T5 has a .86 overdrive. What is your anticipated tire diameter?

[enjenjo]

A S10 T5 has a .86 overdrive. What is your anticipated tire diameter?

The overdrive ratio varies with the ratio between the input shaft and cluster shaft. So the same overdrive gears will give different OD ratios depending on the gear set installed. I did one for a car with 12" wheels, a 4.11 rear end and a V860 engine. The owner wanted as close to a .50 overdrive as he could get. I finally came up with a 2.95 first gear, gear set, with overdrive gears that would give him a .57 overdrive. He was happy with that, so I built it for him. Once it was in the car, he found that it was a bit sluggish in overdrive under 60 mph. So he installed a blower on it! He's happy now.

[kb426]

^^^^^^
I learned something again,

[Ohio Blue Tip]

I  understand how to calculate the RPM at speed using tire size and gear ratio.  I will be changing the 9" gear to a posi and a new gear.  I am trying to find the best RPM to run at 75 MPH all day long.
The engine's peak torque is about 2400 RPM.  I find answers from 1200 to 3000 RPM.  
I'm thinking I should be at 2100 to 2200 RPM???

By the way, the current gear is a 4:11.

[kb426]

I found this: https://www.jalopyjournal.com/forum/threads/dynod-my-235-chevy-inliner.637927/
My exp. with these engines has been that they don't like too much rpm so less than 2 grand would be where I would want it to run for extended periods. My thought would be that I would downshift to 4th to pass or run up a hill. The trucks that I use to drive would run around 3 grand at road speed but they were screaming and the engines didn't last long.

[enjenjo]

The info I can find says the torque peak is about 2200 rpm, and hp peak is about 3200 rpm on a stock engine,  I would suggest  a cruise rpm of some where around 2400 to 2800 at 70 mph  in overdrive. I would try closer to 2400 rpm if it was me.