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Desoto 2.0


James_Douglas

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I am working in earnest on the specifications for the Desoto 2.0 rebuild.  I have been using the car in its mostly stock configuration since 2002.  The 251 with a 3-speed and BW OD has carried us around all of California and daily here in San Francisco well.  But, it is time to create a "final package" that will see us using the car to travel the USA in retirement and onward to the grave.

 

I have the actual guts of the 265 replacement block all down on paper.  Pretty much the usual stuff.  The induction system is going to use two Rochester (GM) series single TBI units on an Edmunds manifold.  It will use one of Langdon's HEI's which he can build as an HEI8 and the computer will run the carbs and the ignition.  Do remember that from sea level here in San Francisco to 10,000 feet that one looses about three percent power for each 1000 feet of elevation with a carburetor.  With TBI, that will not be a factor.  Given the 5500 pound travel design weight...that is a good thing as looses 30 HP with that much weight would not be fun on mountain interstate freeways.

 

My biggest challenge is what transmission to use.  For old age a full automatic is required - - - right Don ? 

 

I have been looking over the torque and horsepower curves and applying the gearing of various transmissions and rear-end gears to see what looks like the best match.  The problem I keep running into is the weight of the car.  My 1949 CV has the same engine as the 1947.  But that 1500 pounds makes a BIG difference in going up over the mountains on the Interstate.

 

No matter which way I cut it, I keep coming to the conclusion that I need more than 4 gears.  I am loath to head down that road, but it may be the only way to transmit the 120 to 130 HP to the wheels and not be in the right lane doing 30 in second gear which is what one has to do now. 

 

I talked with Pat at Wilcap and I could get him to custom make one of his 700R adaptors to the 5,6 or 8 speed automatics.  I shutter at the thought of the time and cost for a custom plate.  I have been talking to the big transmission players and there may be a ray of light from that end.  A couple of them are making transmissions (5,6 &8 speed) for retrofit use by changing the bell housings so that they will bolt up to a standard old "SBC".  I am investigating if I could use one of those transmissions with the off the shelf Wilcap adaptor.  Those companies have stand alone controllers they sell for those transmissions do I not have to worry about the engine TBI computer controlling the transmission.

 

When I plug in a 6 or 8 speed transmission into the RPM - Gear calculators such a combination can keep the 265 in the middle of the torque band and the RPM's in an acceptable up the mountain driving range.  Again, for the weight of this car.

 

I thought I would post what I am up to and solicit constructive thoughts on the path I am heading down. 

 

Best, James.

 

 

Edited by James_Douglas
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I see no mention of a rear end swap to accommodate the increased HP and torque. Have you considered a rear with lower gears? After all,you are going to end up with a 5 or 6 speed transmission with overdrive,so you can go a bit lower in the rear to improve your low and mid-range torque,and still have lower RPM's at your cruising speed.

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I have a 700r4 in my Studebaker.truck (3500# empty.  It's a four speed out of a late Chevy Caprice wagon so weight is probably what you are looking at. It is feeding a Ford nine inch that has a 3.7 something to 1 gearset it is out of a late 80's t bird aProbably form a v6 and provides disc brakes and cable op parking brake that acts on the caliper pistons.  I think they were available with a 3.5something gear set also.  For riding around in the unloaded truck, first gear is too low, second and third are good and fourth is a .73 od.  Engine speed at 65 with 235 75 15 tires calculates to 21/2200. Probably in hilly territory it would spend most of it's time in 3rd. The various gear sets for the 200 and 700 r 4's are available on the web. Good transmission cooling is a must for the r series auto so an auxiliary cooler as well as radiator plumbing with  good air flow is a must, even a fan if you are doing lot of stop and go and mountain climbing I think the later e series gm trans need lots of computer input so that might be a challenge to get them thinking right..

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Thanks for the thoughts on this...let me try to address some of the comments...

 

The rear-end gears will be decided on once I have picked a particular transmission.  The 6 speed and the 8 speed, if they can be used have really low first and second gear.

 

The Desoto has about 4700 pounds of curb weight.  The long trip weight comes in at 5500 pounds.  I cannot over state enough how bad the hill climbing is with that weight. A regular sedan or couple just runs up a hill in comparison.  For any of you that have driven into San Francisco from the north to the Golden Gate Bridge you know it is quite a grade. When I was rebuilding the car (stock) in 2003 and had the interior out except the front seat it would fly up the grade.  Once I have the about 500 pounds back in, it was quite labored.  Basically the power to weight ratio in this car is getting to the tipping point where when trying to pull up a hill gravity is overcoming the available power in the transmission 1:1 final ratio with a 3.9 or 4.11 gear set.  I happen to have both and the 3.9 works better with the 3-speed and the OD here in city driving.

 

I ran across some references of a guy who had a 1957 Chevy with the single injector throttle bodies on his stovebolt 6. Turns out that those throttle bodies are within 4MM of intake holes of my Edmunds dual 1BBL manifold.  After some searching I found the man who did the FI for that Chevy.  He builds the systems using plain jane GM parts that one can get at any auto parts store. According to him, you only have to use one O2 sensor.  My gut tells me that two would be better, but a plain jane GM computer does not have the capability for two.  You could use a Megasquirt and it can read two sensors. 

 

He also told me he got the HEI8 from Tom and so the computer can deal with the timing as well.  A knock sensor on the flathead would not be a bad thing pulling up the mountains.

 

James.

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18 hours ago, James_Douglas said:

I happen to have both and the 3.9 works better with the 3-speed and the OD here in city driving.

 

I think I would try first before the big jump to a 6-8 spd. transmission would be to just putting in a 3.73 rear original Mopar 3rd. member and hooking up (wiring) your existing  OD to shift in and out with a push of a button or switch to give a usable 5 spd. by using what you already have. First gear in OD is pretty much useless , not enough change to make it worth the effort other wise it is a 6spd..

 

At least on flat land you should be able to 75 mph all day long. Cannot say what you MPG would be however!

 

Your limiting factor is the HP available versus your weight. NO transmission is going to solve that. More gears is a help but 5 gears will give you about all you are going to get??

 

Like the FI addition though!

 

One opinion which is you asked. ?

 

DJ

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Actually torque is your limiting factor in pulling. To give an example of what the additional gears will do. My nephew and I each had new Dodge diesel pickups same year both with the HO engine for that year. I had a 4 speed auto, he had a 6 speed manual. i had cheated and added a tuner to my truck. We had stock trailers of the same size and roughly the same weight of cattle in each. I thought i would eat him up with the tuner and all. He just walked all over me by being able to stay in the power band of the diesel longer with the extra gears he had. On flat ground i could catch up, but man in the hills he would just eat me alive.

My point being that i think Greg's idea of more gears is right on the money! He only has a 4 speed now so more gears before OD or a lower gear set with two OD's will help.

Just my thoughts.

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Hi I built this exact car ;50 desoto edmunds dual intakes Langdon hei dizzy  and his pinto 2 bbl carbs ,it had a tiptoe trans and I recently put in a three speed with a borg Warner overdrive ,the car has a 3.9 rear end that went with the tiptoe Now with the 3 speed manual  she lugs a bit in first ,to replace the original start off slow ooze  start with  the automatic transmission ,so I don’t think that making it perkier is going to happen .My next move was to put a 3.5 rear end in the Mopar a 41-48 Chrysler or other Mopar rear end from that bracket of time will be a 3.5 and a easy fit .you may have to change the yoke witch  varies amongst Mopar products .

another thought might be a 8.8 ford rear axel ,not the pricey famous 9” .ford ranger truck has’m this is a 3.2 it’ll have the same wheel pattern as Chrysler ,but I don’t know if you would pass the Moser test .

this is going up,MoserSt from San Pablo blvd in el cerrito near you !

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Here you go.

Do this with a 383 or 440 minus some of the things this owner did you do not like or want.

Your lack of power will be over and at least its not a damn SBC and 700R.

 

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Edited by 55 Fargo
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I agree that a v-8 would make Mr. Douglas' sedan a better road car,  but I doubt he is interested....

 

Any of the late 5-6-8 speed automatics will entail some major R&D for an adapter as well as the computer to make them work. They are becoming 

horribly overburdened by technology. That said, you might also look at the Mopar units from the 5.7 and such.

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