Is 4th gear 1:1 ratio?

[Iowaboy]

I am trying to calculate what rpm I have to run to hit 60 mph. 

My rear end is stamped 41F, I assume this means 4.1 ratio. My rear tires are 28.25 inches in diameter,  if 4th gear is 1:1 then I have to hit 2926 rpm to run 60 mph. That seems kinda high rpm for a flathead 6. 

[59bisquik]

As far as I know, the 4th is a 1:1 ratio. Gotta remember these trucks were never designed to go the highway speeds of today.  Probably not too many cars and trucks traveling at 70+ back in the 50’s.

With shorter tires and 3.73’s, I calculate about 3200 for 70mph in mine. I drive the freeways of SoCal all the time and hold her at that speed with no issues.

[greg g]

Got a 4.11 in my coupe, 65 indicated is 62 over the road, calc with 225 75 15 works out to 3280 rpm.  The old fellow who did my machine work told me 80-85% of peak HP rpm (3600) makes for happy motoring.

[55 Fargo]

4 hours ago, greg g said:

Got a 4.11 in my coupe, 65 indicated is 62 over the road, calc with 225 75 15 works out to 3280 rpm.  The old fellow who did my machine work told me 80-85% of peak HP rpm (3600) makes for happy motoring.

This of course would be qualified by a sound engine in good internal condition.

I know this has been your experience for a number of years to date.

Mine I run at 2400 RPM for 62 mph or 100kmh but I have 3.23 gears.

These old brutes can handle this far better than any Stovebolt splasher or Banger engine that's for sure.

[greg g]

2925 rpm according to http://www.4lo.com/calc/gearratio.php

[Iowaboy]

I knew that engineering degree would come in handy. LOL

 

[TodFitch]

19 hours ago, Iowaboy said:

I am trying to calculate what rpm I have to run to hit 60 mph. 

My rear end is stamped 41F, I assume this means 4.1 ratio. My rear tires are 28.25 inches in diameter,  if 4th gear is 1:1 then I have to hit 2926 rpm to run 60 mph. That seems kinda high rpm for a flathead 6. 

Mopar engine designs of that era had to survive 50 hour tests running at max BHP. That would be at 3600 RPM

9 hours ago, greg g said:

Got a 4.11 in my coupe, 65 indicated is 62 over the road, calc with 225 75 15 works out to 3280 rpm.  The old fellow who did my machine work told me 80-85% of peak HP rpm (3600) makes for happy motoring.

I've seen that 80% or 85% number in a number of places and believe that was (and perhaps still is) a pretty good rule of thumb. So basically the engine, if in good condition, should run happily all day at 3000 RPM. I have a personal preference for not exceeding 3200 RPM on long "high speed" drives which works out to about 60 MPH in my older car (190 cu.in. fitted with the stock 4.375:1 rear end and skinny 17" bias ply tires). Above that speed the car begins to be a bit uncomfortable with respect to its suspension, etc.

With your tire diameter, my calculator shows you running 66 MPH when at 3200 RPM (assuming a 4.1 rear end).

 

[55 Fargo]

Interesting enough these engines can run in the 2500-3000 RPM range and be happy with it.

Try this with a 216 Stovebolt  ,babbit pounder splasher Chevy engine, not going to be too happy and might self destruct.

I do not think these engines like to be run below what 2000 rpm, necessarily, and are comfortable in a higher RPM band