Over drive RPM in OD ?

[rustytoolss]

I have thought of installing an A500/A518 into my B body wagon for some time now. My current axle ratio is 3.23 and a tire dia under 27.00" . the over drive is .69/1 which would give me an RPM of around 1850 ( or so) at 65 MPH. I do have a stock converter. The engine is a 1962 Poly 318. Would you think that the RPM of around 1850 would be a bad thing at 65 MPH. I'm suure that a 3.55 would be a better choice. But like I said the car has a 3.23.

 

[33 IMP]

Late model multi-speed trans/rearend combos can run that easily, BUT. They have electronic trans control for easy downshift and converter unlock if lugging is detected. Not to mention fuel injection and computer controlled timing.
I think it might work for you IF you can get it to downshift out of O.D. easily, if necessary. A control switch for the o.d. on the shifter might work. And 9f course, if you have a good handle on the cruise rpm tune-up.

 

[Rishi]

I don't see any obvious reason why 1850 RPM @ 65 MPH is a problem. That is actually pretty sweet and economical. Maybe NOT very performant, but with a 318, we may not be after tiny quarter mile times.

The overdrive allows us to move to higher gear ratios for improved performance at lower gears, without the need to strain the engine at highway speeds.

I got a friend with a daily-driver 426 Hemi with 4.89 gear ratio. While he doesn't drive it daily, he is kind of locked in how far he is willing to drive, because with his 727 transmission, at highway speeds of 65, his engine is turning around 4300 RPM. His setup would greatly benefit by an overdrive.

 

[66 Sat]

I think that rpm might be a little low. When I got the TKX for my car I went with the .81 O/D 5th gear and not the .68, because I felt that the small block wouldn't have the torque to pull the higher ratio comfortably. My engine is a 318 poly stroked to 354, 3.23 rear end, 25.6" tire.

I think I made the right choice as the rpm can drop to 2,000rpm on steep inclines on the highway and 5th gear is still fine. The .68 ratio would have been too much and I'd need to shift down to 4th.

On the flat you probably won't have an issue, but it's the grades that might cause problems, especially as at 65mph you're fighting the wind and a heavy wagon as well.

If you can't alter the O/D ratio on the gearbox then you may well need 3.55 or 3.91 gears.

 

[451Mopar]

Pretty much the RPM range of newer cars, you can always shift out of overdrive it you need to

 

[rustytoolss]

I think that rpm might be a little low. When I got the TKX for my car I went with the .81 O/D 5th gear and not the .68, because I felt that the small block wouldn't have the torque to pull the higher ratio comfortably. My engine is a 318 poly stroked to 354, 3.23 rear end, 25.6" tire.

I think I made the right choice as the rpm can drop to 2,000rpm on steep inclines on the highway and 5th gear is still fine. The .68 ratio would have been too much and I'd need to shift down to 4th.

On the flat you probably won't have an issue, but it's the grades that might cause problems, especially as at 65mph you're fighting the wind and a heavy wagon as well.

If you can't alter the O/D ratio on the gearbox then you may well need 3.55 or 3.91 gears.

I think the 3.23 is worth a try. But if the RPM is just to low, I would look for a set of 3.55s. My poly engine is stock . The car is just going to be a fun driver.

 

[furious70]

With an auto it might be ok, with a stick I'd say too low. With a stock cam it might be ok that low, but 50yr old cam and open chamber heads aren't very efficient at low rpm

 

[furious70]

With an auto it might be ok, with a stick I'd say too low. With a stock cam it might be ok that low, but 50yr old cam and open chamber heads aren't very efficient at low rpm