question on gear ratio w/ od

[DJ194950]

i've got a 50 4 dr. with a rebuilt stock p-24 engine made into a 230 ci.

currently running a r-10 od trans with 3.9 rear gears. has plenty of power avail in third overdrive.

i've got a 3.73 rear and a 3.54 that i can buy reasonably.

q. has anyone ran the 3.54 gears with the overdrive? is it too much?

cost isn't the concern here, just all the labor.

appreciate your imputs,

thanks all,

doug

[Plymouthy Adams]

using the 3.54 in OD is effectively a 2.5 final drive..on flat terrain you may be able to get away with that..long slow grades may tax the engine prompting coming out of OD...using the 3.9 in OD is effectively 2.73 final drive and is factory acceptable..as it was offered as a factory kit to the dealer to install in earlier production vehicles..it was my understanding it was to help move the 1951 model cars off stagment sales lots..these cars had stock 3.9 ratio final drives and the rear gear stayed as such...my 51 wagon was such a set up..

if you have the OD..I would keep the install as simple as possible and give the rear gear you now have a chance to do its job..that way you have all the power on take off and stil be effective in OD..hill/grades..simply go back to 1:1

[blucarsdn]

Factory equipped OD vehicles always have a lower rear ratio than non OD vehicles. The 3.9 ratio with tire size close to the original size would work best, a 3.54 would over gear the car which would lug the engine.

I have 3.23 ratio in my '39 Plym, 21560R15 tires with a AOD trans and a 330HP V8, it is pulling 2,200 RPM's at 65/70 mph, the same as most modern cars.

Of course my tires are smaller that 600x16/670x15 and I have three times the HP of a flat head six.

[1941Rick]

I agree with the above....3.9 is the way to go....remember you only have so much power to work with.....love the flatty

[Don Coatney]

I have a Desoto long block 255CI flathead in my P-15 along with a T-5 overdrive transmission. I am using a 3.55/1 differential. This differential gearing works well with my engine but I have doubts it would work well with a 230CI engine. I would think a 3.9/1 would work much better.

[DJ194950]

i guess i'll run what i got-3.9 rear for now.

keep the 3.73 for a time when nothing else is left to do on the 50.

i hope to build a teardrop type trailer this winter and go travlin the the 50 and trailer next summer, so the 3.9 will be left in. buy the 3.54 for next project? maybe i'll live that long.

relatives in washington st., b.c., montana, colorado, ok., n.c., virginia.

seems very long ways off, but with the speed that my rear frame and quarter panel replacement job is going:eek:, thats probably being very optimistic.

thanks for the imputs

doug

[Jim Yergin]

Doug,

Where in Virginia?

Jim Yergin

[DJ194950]

a cousin that i've always been close to, the brother i didn't have, has been living in the falls church/ fairfax area for the past 30+ years. he recently moved again to a differant town that i don't remember the name, but still in the area. it's been several years now that we have'nt been able to meet on either coast. it's my turn to make it east.

i may be dreaming about driving the 50 out, but it's been a long time since i've done a road trip/adventure. love the idea.

are you living near the west side of d.c. in virginia?

maybe you could give me a ride in the woody with the o/d now working?

if it ever comes together some plymouth/mopar meets on the agenda would really be great!

doug

[Jim Yergin]

Doug,

Just let me know when you are coming. I am about 35 miles southwest of D.C

Jim Yergin