CRUISING RPMS ON 41 PLYMOUTH FLAT 6

[juspasinthru]

I have seen several threads on this using the search feature but what is the easiest way to cruise at 65 at lower rpms?

overdrive unit? if so where do you purchase and how much?

t-5 conversion? if so what is the most updated list of parts and instructions?

 

lots of info out there on this some old and some conflicting.

thank you guys

[Loren]

What I would say only applies to my car (1952 Suburban).

I recently bought a Plymouth Overdrive transmission on eBay. I had been watching for sometime and the going price for one in unknown condition was $800. This one had been gone through and had a new relay, the wiring harness, kick down switch and as a bonus the drive shaft. It had also been set up for 12 volts. It was near by so I picked it up myself saving a shipping bill. I paid $1,100 and figured it was a good deal. Overdrives became available around May or June 1952 for the post war cars. The B-W Overdrive reduces engine speed by 30%. There are calculators on the internet for tire rotation per mile (for commonly available modern tires) and final drive ratios. A friend gave me a rear end from a 1954 with a Powerflite transmission. This was a cheap and easy way to get a lower numerical ratio (3.73) and all of it is stock stuff. It's just arranged in a way the factory never intended. Factory built Overdrive cars used 4.1 final drives which gave them better acceleration but didn't give them top speed potential. Now something to consider, is that one is not going to "speed shift" a Plymouth transmission (or any 3 on the tree Overdrive for that matter). I have a T5 in a Model A and I don't care for the ratios at all (I am told there are other ratios available such as for a Camaro) but it is modern and does shift quicker with less drama. So that is an option. For me I was not going to cut a hole in the floor of my car for a shifter. So three on the tree works for me.

Gear ratios will get you to modern Highway speeds but.... will your engine have the torque to pull them?

Which means now you have to do some engine work. One thing I haven't heard on this site is the idea of restricting the size of the holes drilled in the block to the cam bearings. The oil passages go to the cam bearings first and then to the Crankshaft main bearings and finally thru the crankshaft to the rod bearings. Many production engines are that way (even the mighty Ford FE 427 that won LeMans). For racing there are kits for these engines to restrict the flow to the cam bearings which sends more oil at greater pressure to the crankshaft main bearings. Plymouths have oil passages about .250" the common restrictor size is .065 to .070. So you see there's a lot to be gained! There are no secrets to getting more power however keeping the engine alive is of greater importance.

 

[Go Fleiter]

Overdrive is the best improvement I ever did to my 51!

Engine does 2100 rpm now at 140 kmh = 87 mph - but remember the weak brakes!!

 

I believe- but I don´t know for certain- that the 41 6 cyl. accepts a later transmission.

A tranny is needed with a bach hole to let a shift rail pass to the overdrive unit mentioned above.

As far as I have understood, this is to allow OD to be engaged in 2nd or 3rd gear engaged (not 1st or reverse)!

Maybe, shortening the rail will do without passing into Your existing tranny but You must remember leaving the

OD off in 1st and reverse. I have no knowledge on this kind of setup.

You don´t need a automatic trans, handshift is ok.

 

This is needed to allow OD to be engaged.

- OD Solenoid, an electrically activated system to engage the OD by a clever 2-step plunger push rod

- speed switch ("Governor") asking ~25 mph

- shift rail switch ("lock out switch") and its handle-and-bowden- cable activation

- OD- Relay beeing powered

- 2nd or 3rd gear engaged (not 1st or reverse)

 

If putting the Handle and shift rail to "OD engaged", You will get a free wheeling under ~25 mph (OD disengages because of .

When OD

 

Kickdown or not:

I don´t like the brutal funktion of the kick down switch,

beeing installed originally on the carburetor :

1.) actuation is mechanically very serious and heavy,

forces I won´t like to have on the carb body itself.

2.) grounding of the ignition seems to brutal to the engine to me

 

So I didn´t install that system: if something like kickdown acceleration is really needed,

a handswitch to interrupt the current to the OD relay does, and I have to take my foot from the gas pedal

for one moment to relieve the drag from the OD.

OD solenoid can disengage (or engage) OD only when dragless,

It can be activated and wait for the opportunity (no drag) to engage the OD .

 

Sources:

Blueskies or blue-skies Pete Anderson of Idaho did a nice explanation on his OD installation:

I had to google for a while to find this:

http://www.oldwillysforum.com/Plymouth/05-tra/tra.html

 

Greetings from Düsseldorf!

Go Fleiter

These are my modified plans, mine is minus grounded!

Edited September 1, 2019 by Go Fleiter

[greg g]

I have about 2000 miles on my car since I installed a BW r10.  My car has the 4.11 to 1 rear gears.  I usually cruise at 60 or so on the highway, 65 indicated on the interstate.  Without the OD, this had my engine turning at about 3200 rpm.  No with the OD, I don't drive any faster, but the 30 percent reduction takes engine speed down by 900 rpm.  Much more relaxed.  The 230 seems more than adequate to pull the hills around here with OD engaged.  My governor doesn't kick in till around 40, so I don't use the OD around town or try to use it in second gear.  I found a core locally, and one out of town, bought both for 350.00 and then had them made into 1 unit and had it attached to a 56 transmission that had come with my engine.  George Ashe did the work for 450.00. plus a couple transmission cases I had. On the highway on extended trips Gas mileage is 20 / 21.

[Bobb Horn]

My 38 Coupe has a 218.    I went through three stock transmission, 3.9 rear gear.    Very many RPMs at 55 mphs with this setup.     I installed a TK5 speed Ranger transmission, and used the 3.7 Ranger rearend.      My RPMs run about 1800 at 55 or 60 mph.     Torque is very good with the 218, and good gas mileage also.

[Loren]

I just sold an 1964 International Travelall that had a T86 with R 10 Overdrive transmission. I've been told the Plymouth Transmission with Overdrive is a better gearbox. I really liked the Overdrive feature especially with a smallish engine. (The IH had a 266 V8) There's a pretty good hill near my home which at about 3/4 of the way up would trigger the kick down. Once you crested the hill and lifted the throttle a little it went back into Overdrive. Getting it into 2nd gear Overdrive took the right situation and practice. I am sure most people wouldn't bother. A flathead Plymouth seems to be the perfect car for an Overdrive transmission. Overdrives have a certain charm to them and Plymouths are cruisers which amplifies that charm. If you don't use the "Automatic" feature of the B-W Overdrive, I think they are kind of pointless. In other words if your Overdrive doesn't work like it was intended automatically, I'd either fix it or get a different transmission. Using it to get "one more gear" is not enough to justify the trouble of having it. A T5 shifts faster, easier and has a synchro first gear. There's not much "charm" to a T5 though. I've driven foreign cars with the Laycock-DeNormanville Overdrive which are not "Automatic". You have to flip a switch or toggle a lever to switch between direct and Overdrive. Honestly, I'd rather have a 5 speed than a 4 speed with non-automatic Overdrive. L-D did not put the governor and kick down switch in because they figured the Overdrive would be engaged under full throttle most of the time. The L-D Overdrive was to be installed in sports cars, while the B-W was designed for full size American cars and trucks. Different designs for different vehicles and uses.

 

The freewheel feature should get some mention. First of all parking the car in gear does not ensure it won't roll. You've got to pull the Overdrive handle to lock the freewheeling. However, if you master it you can shift without using the clutch. You have to let the engine RPMs drop below the drive shaft speed to do it, then slowly raise the engine speed till they match then accelerate normally. I raced SAAB cars in SCORE Desert and Baja races. They had a dedicated freewheeling unit (it was a hold over from the 2 cycle days. Two cycle engines don't get as much lubrication when the throttle is closed, as the fuel carries the lube oil). I loved it as you could down shift going into a corner then power out without touching the clutch. I used it like a kind of "Pre-select". I suspect this has a limited application for a Plymouth as you will never rev one 7,000+ rpm. So the question is "Charm" and highway speed or modernity? You can put a V8 with an automatic in your vintage Plymouth and perhaps a front frame clip from something else for better steering and brakes, but what do you have afterwords? It will only look like a vintage Plymouth. There's something rather 2D about such a car. My choice would be the best example of what was available at time the car was made. That way it retains all of it's charm.

[HotRodTractor]

Just for reference - my P15 does about 2050 rpms at 65mph in overdrive using a T5 transmission and 3.55 gear out back. The car easily does 80mph. Granted its a 251ci engine with dual carbs, dual exhaust, cam, dual point distributor, etc.... so its got a few ponies over a stock. Don installed this transmission and rear axle - but I have a similar T5 and even newer rear axle with disc brakes for my Pilothouse that I picked up for $100 each.

[chrysler1941]

On 9/1/2019 at 9:41 PM, Loren said:

You can put a V8 with an automatic in your vintage Plymouth and perhaps a front frame clip from something else for better steering and brakes, but what do you have afterwords? It will only look like a vintage Plymouth. There's something rather 2D about such a car. My choice would be the best example of what was available at time the car was made. That way it retains all of it's charm.

 

Exactly. Same goes for 12 volt, radial tires, etc

[laynrubber]

I finally got my OD to work (mostly at least...I have a reverse issue) and I am really impressed. At 65 mph it shows 2400 rpm. It all was bolt on, there were some operational issues to work through but I considered a T5 and some sort of adapter kit for an automatic installation....the Borg and Warner R10 was the easiest.

[9 foot box]

   When the OD is engaged, it locks out reverse. If that's your problem.

[greg g]

My literature says to make sure the of is disengaged via the control cable before reversing. It says attempting to reverse while engaged will damage the sun gear assemlbles.

[DJ194950]

It depends, if you have wired it up as stock and you are going slow enough to try shifting into reverse, OD should be disengaged anyway due to the governor will not be grounded, if it working  properly. you should be able to shift in reverse.

 

Now if it is bypassed on the governor where it could still be engaged when stopped, you will Not be able to get into reverse. It is mechanically locked out, as in the shift lever will not let it move towards reverse gear.  I know from my own experience.    

 

Now Greg are you saying it will shift into reverse position on the lever but will not move the vehicle rewards because of the freewheel effect with the cable still pushed in?

 

DJ

Edited September 9, 2019 by DJ194950