Chris mathiesen Posted June 30, 2014 Report Share Posted June 30, 2014 I posted yesterday regarding a 383 conversion in my 1946 plymouth. My reasoning for the swap was for speed. I currently have the stock flathead six with a 12 volt conversion and the car is maxed out at 55 mph. I was thinking about using the wilcap transmission adapter and bolt in a 700r4 overdrive transmission. I was wondering if this transmission conversion will get me more speed. What other things could I do to get the stock flathead to hit 65-75mph? I have been told the transmission conversion with a change in the gearing would help. Just looking for some guidance. Thanks! Quote Link to comment Share on other sites More sharing options...
TodFitch Posted June 30, 2014 Report Share Posted June 30, 2014 Since my '33 with its stock drive train including a 4.375 rear end is fully capable of cruising at between 60 and 65, it seems highly likely to me that if your '47 is "maxed out" at 55 then something is wrong with it. It should be able to cruise at 65 in stock configuration with no problem if it is in good repair. Now I'll step aside and let others tell you about transmission and rear end options that can reduce the engine RPMs at speed. Quote Link to comment Share on other sites More sharing options...
DJ194950 Posted June 30, 2014 Report Share Posted June 30, 2014 What's your current rear end gear ratio? You could have a 4.1 ratio best for mountainous terrain. Or could be 3.9 which most have. At that ratio you are not at max. rpms or even close. It may sound that way if your not used to old car normal fan noise. You should be easily cruise at 70 all day long. Get used to the noise. Put on a tach. Run it it up to 3600 and see how fast you go. The motors were factory tested for days on end at that rpm. Of course your motor must be in good condition to do this! Maybe find a 3.73 gear stock gear set. They are out there. My 50 4dr. has 3.9 rear w/ the mopar R-10 OD trans and easily runs 70-75 rather quietly. Considering trying a 3.73 rear gear as I believe it will still perform well and be quieter and get better gas mileage. All way easier than a v-6 or v-8 swap and way cheaper! Car people also are more impressed with a stock motor that Runs well with traffic! Your choices, DJ 1 Quote Link to comment Share on other sites More sharing options...
Daliant. Posted July 1, 2014 Report Share Posted July 1, 2014 (edited) If your maxed out at 55 mph I don't think overdrive is going to help, I'd say the engine is tired or needs a good tune up. Do a compression test to see if the rings are in good shape, a leak down test would be better though this will let you know if the valves are sealing. You should be able to hit 70 with the stock engine/trans/rear combo. Edited July 1, 2014 by Daliant. Quote Link to comment Share on other sites More sharing options...
halffast52 Posted July 1, 2014 Report Share Posted July 1, 2014 what size tires are on it when I bought my coupe it had 15 inch 60 series low pro's they were 22 inches in diameter the old flathead really seemed to work hard at 60 mph even after I rebuilt the flathead so after reading a lot of posts on this site I swapped the lo pro's for a 15 inch tire that was 28 inches in diameter and since then it will cruise 70 all day long without sounding overworked ..best of luck on whatever route you take with it ...................................................................Dan Quote Link to comment Share on other sites More sharing options...
Robert Horne Posted July 1, 2014 Report Share Posted July 1, 2014 My little 38 Coupe at 55mph was doing a lot of rpms, 3 speed trans, 3.9 rear, 235 tires. I installed a Ford Ranger TK5 five speed trans, 3.73 rear. Now the Coupe at 55mph is doing about 1600 to 1800 rpm on level road.. Quote Link to comment Share on other sites More sharing options...
Don Coatney Posted July 1, 2014 Report Share Posted July 1, 2014 A 1946 Plymouth is not a new car. You cannot expect it to do what a new car will do. The car related TV un-reality shows make it look simple to just drop in a new engine-transmission-etc. The car magazines are full of articles written to sell the products that the vendors pay big bucks to advertise in there magazines. I have seen many folks buy a old car and think that it is very simple to make these upgrades-modifications as the TV shows and magazines make it look easy. So they go that direction without a good plan or understanding of the scope of the project. Once they find out they are way over there heads due to the high cost and the amount of work involved they lose interest and the car is frequently scraped. I say all this just to make you aware of the things that I have seen happen many times. Modifying and even maintaining an old car is a lot more involved that most folks realize. It is much like a line in the sand that never stops moving. The tools and skills required can be overwhelming to even seasoned craftsmen. So I recommend you develop a plan and do this project one step at a time always keeping in mind that failure is not an option. Go to the resource section of this webpage and read everything there. Buy a service manual and any other books such as Motors manuals that will be helpful. Learn everything you can about every step of the project before turning the first wrench. Use the search function of this webpage to see how others have done things. 4 Quote Link to comment Share on other sites More sharing options...
wayfarer Posted July 1, 2014 Report Share Posted July 1, 2014 I posted yesterday regarding a 383 conversion in my 1946 plymouth. My reasoning for the swap was for speed. I currently have the stock flathead six with a 12 volt conversion and the car is maxed out at 55 mph. I was thinking about using the wilcap transmission adapter and bolt in a 700r4 overdrive transmission. I was wondering if this transmission conversion will get me more speed. What other things could I do to get the stock flathead to hit 65-75mph? I have been told the transmission conversion with a change in the gearing would help. Just looking for some guidance. Thanks! For any trans swap where the oem bellhousing is replaced, you are back to some fairly major fabrication. I have outlined some of the basic stuff on my web site: http://www.qualityengineeredcomponents.com/?page_id=222 If you feel the need for a (relatively easy) OD package then I strongly recommend a hard look at Robert Horne's swap. As others have indicated, make sure that the engine is running right first. Quote Link to comment Share on other sites More sharing options...
Lumpy Posted July 2, 2014 Report Share Posted July 2, 2014 (edited) Sorry to keep posting so much discouragement. !!! Maybe a 1946 Plymouth is not a good "fit" for you. I'm thinking you'd be more satisfied with a mid to late 1950's car, or perhaps something in the 1960's. My '48 Dodge's "sweet spot" is around 55mph. It will do up to 65 just fine, but I only go 65 if I'm holding up traffic. Most of the highway speed limits around Spokane Washington are 55 to 60mph. The freeway as it goes through Spokane is only 60mph, and then picks up once it gets out of town. I consider myself very lucky in that respect. I don't think the real enjoyment of these cars comes from blasting down the freeway at 75mph (and in which case I would endorse disc brakes) or running a constant 3600rpm. I think that the back roads and secondary highways is where they shine. I drive my Dodge to enjoy it, not get from point A to point B at 75mph. If I want to do that, or just have the need for speed, I get on one of my motorcycles, or my 360 Dart. It's very likely that you live in a big city, in which case the freeway is not a great place to be in an old car, and stop light to stop light gets old pretty fast. I understand that...I grew up in L.A. Now even Spokane is too big for me, and I avoid going there as much as I can. But I know what it's like to be going 55-60mph on a freeway where traffic is moving at 80mph. Again, I'm assuming you must live in an area where stop light to stop light, or a congested freeway are your only options. I'm thinking that the R10 overdrive transmission would be the swap for you, and perhaps raising the rear gears a bit at the same time. ?? That would be somewhat simple, lots of guys on this forum that could walk you through it. And again, I think the drum brakes, when in perfect condition work fine, but in your case, if you are that serious about blasting along at 75mph in a 1946 Plymouth, you probably really want to put some disc brakes on the car, and there are also many on the forum that can walk you through that. Okay, sorry to be a big downer, but there's no simple, easy or cheap way to make a speed racer out of a 1946 Plymouth. k. k. Edited July 2, 2014 by Lumpy 1 Quote Link to comment Share on other sites More sharing options...
martybose Posted July 2, 2014 Report Share Posted July 2, 2014 My 47 is a hopped up flathead with an R10 OD unit. When I moved it from San Leandro to Galt my daughter was following me, and commented afterwards that she was surprised when I went up the Altamont Pass at over 70 MPH. Had to think a little, because I thought I was only doing mid 60's in 3rd over, until I remembered that I had put taller rear tires on the car but hadn't calibrated the speedometer to them yet. The old girl wasn't even straining. Marty 3 Quote Link to comment Share on other sites More sharing options...
st63 Posted July 2, 2014 Report Share Posted July 2, 2014 (edited) My stock 41 coupe with the flat head six will do 60- 65 all day long with the stock 3 speed and 4.11 rear axle. It just takes a little time to get used to the sound of traveling at about 3200 rpms with 70 year old sound proofing technology! If you're gonna try to go faster, then you're opening up a whole can of worms, as the brakes, suspension etc aren't built for it....so then you have to upgrade everything. Pretty soon it's not a real 46 Plymouth anymore, just another dime a dozen "resto-mod". An R-10 is the best solution if you really want to cut down the rpms... as at least it's a period appropriate upgrade that the drive train is capable of handling....The other option is one of the optional 3;73 rear ends that were available...but you're giving up low end acceleration. Cheapest option....get used to its capabilities and learn to love the sound of the stock flat head six at higher rpms. Great link: http://www.ply33.com/Misc/speed Edited July 2, 2014 by st63 Quote Link to comment Share on other sites More sharing options...
TodFitch Posted July 2, 2014 Report Share Posted July 2, 2014 . . . Cheapest option....get used to its capabilities and learn to love the sound of the stock flat head six at higher rpms. Great link: http://www.ply33.com/Misc/speed +1 and I like the link too. 1 Quote Link to comment Share on other sites More sharing options...
st63 Posted July 3, 2014 Report Share Posted July 3, 2014 (edited) Ha Ha, Yeah, your ply33 site has been very informative...keep up the good work! Edited July 3, 2014 by st63 Quote Link to comment Share on other sites More sharing options...
Tim Keith Posted July 3, 2014 Report Share Posted July 3, 2014 (edited) I don't want to go so fast, that's part of the reason that I like these old cars with manual steering, manual brakes, roll up windows and AM radio. Going 60 with a little more available is a reasonable goal. When in good stock shape many of these cars could hit 90 mph on a flat stretch of highway. You don't need a 383 to go beyond the legal speed limit. A Jeep 2.5 four with stock 130 HP would do that in a P15 - not that anybody would care to see the four cylinder motor on cruise night. I'd not use the 700R4 as its really intended for an older V8. The 700R4 has greater internal power loss than the 200R4. A 200R4 or a manual five speed is probably better. The R10 overdrive is great if you can find one and probably worth the wait as it'll work as is. A neighbor has a '36 Ford truck with plenty of patina and a big Chevy V8, a beer keg for a gas tank, still has drum brakes. He has had this truck since the early 1960s. You can do the V8 swap but be aware of what you have and its limits and it'll be okay. Edited July 3, 2014 by Tim Keith Quote Link to comment Share on other sites More sharing options...
Lumpy Posted July 3, 2014 Report Share Posted July 3, 2014 I'm perfectly happy with drum brakes, and I usually try to encourage people to just completely rebuild the drum brake system, rather than slapping on a set of discs. But I got to thinking that if the OP really desires to fly down the freeway at 75, or more on a regular basis, sooner or later a panic stop is going to happen. I mean, the odds go up. For those of us that keep it under 65, and more usually 50-55, or 60, a panic stop from 80mph is not very likely, and a drum brake system in good condition is fine. I'm thinking that finding a R10, paying the going price for it, and doing the work to put it in, or even paying someone to do it, will be an absolute picnic, and cheap, compared to the other options. I'm not sure what's involved with the Ranger 5-speed trans, but Horne sure does. That might be the way I'd go, if I was considering such a thing, but wouldn't because I'd lose my three-on-the-tree shift, which I think is half the charm of the car. I don't think the OP cares about that. If I came across a free or really cheap R10, I'd slap it in Lumpy just as an upgrade, and still have 3-on-da-tree. k. 1 Quote Link to comment Share on other sites More sharing options...
Tusler 49 New Yorker Posted July 3, 2014 Report Share Posted July 3, 2014 I would like to throw my 2 cents in here if I may. I had a 47 plymouth Super Deluxe 2 door back in 1979 in Ogden, UT. The fastest I could ever get it to go even after I put new Bearings and Rings in that flat 6 was 70mph and it had a manual 3 speed trans. I now have a 49 New Yorker with a straight 8 and what a hugh difference. I cruise it at 60 very comfortably all day. It has enough torque to pull away from a stop in 4 th gear. If you are going to swap stuff, I wonder if a flathead 8 will fit in your car. Or pick up a 48 or 49 chrysler with a L8 in it and you may be happier. 1 Quote Link to comment Share on other sites More sharing options...
pflaming Posted July 3, 2014 Report Share Posted July 3, 2014 (edited) I put a 3:73 Cherokee rear axle in my B3B which has a 3 sp, and I now cruise at 65 mph with the semi's and pass them with ease. May change it to a 3:53 or what ever that number is, but will definitely do a very thorough sound proofing first. Finding a good forum is harder than finding an R10 Overdrive. You found this forum so you are 80% there. R10's are out there, I've found three, sold two, in the past 18 months. Gonna put the one I have into my '54 Plymouth. Just be patient. Good luck. Edited July 3, 2014 by pflaming Quote Link to comment Share on other sites More sharing options...
Robert Horne Posted July 3, 2014 Report Share Posted July 3, 2014 I put a 3:73 Cherokee rear axle in my B3B which has a 3 sp, and I now cruise at 65 mph with the semi's and pass them with ease. May change it to a 3:53 or what ever that number is, but will definitely do a very thorough sound proofing first. Finding a good forum is harder than finding an R10 Overdrive. You found this forum so you are 80% there. R10's are out there, I've found three, sold two, in the past 18 months. Gonna put the one I have into my '54 Plymouth. Just be patient. Good luck. I have a 3:55 Cherokee XJ rearend for backup, just incase my 3:73 Ranger rear did not work out. The XJ would be a closer fit, over the Ranger with spacers. The stock 3.9 was too low with the stock 3 speed trans, and the 5 speed Ranger trans, even in hilly Virginia. . Quote Link to comment Share on other sites More sharing options...
pflaming Posted July 3, 2014 Report Share Posted July 3, 2014 If the 3.9 was too low, then in my opinion, your challenge is not the tranny but the engine. I drove my half ton pickup up to the Sequoia National Park some 50 miles from my home. Home is 300 ' above sea level, Sequoia National Park is 6500' . In that climb is a 10 mile stretch that is a nice test of air conditioners in the summer. In my drive, I never shifted from 3rd gear and the engine never labored, it pulled strong and steady all the way to the top. I'm a novice mechanic but I would do a first class tune up, check the clutch, put on radial tires if you do not have such. That's my humble opinion. I wish you well, coupes can be fun. Quote Link to comment Share on other sites More sharing options...
Robert Horne Posted July 3, 2014 Report Share Posted July 3, 2014 The 3.9 was too low for me, even in hilly Virginia, with the 3 speed. At 55 engine was doing a lot of rpm, had plenty of power to go to 65. The 3.9 was to low also with the 5 speed, in that first gear was like a "granny gear", but the rpm was better at the 55 and 65 speeds, still plenty of power from the engine. With the 3.7 rear, the first gear is great for uphill starts, or dirt/gravel roads, 4th gear great for 45 speed limit areas, and 5th gear great at higher speed areas. At 30mph I can still go up a few degrees incline without going to 4th, and not have any problems. "82hp" seems great for the type driving I do, no Interstate yet. The tach I installed reads about 1500 to 2000 most of the time, power is real good. The engine feels like a truck engine, more than what I would consider a car engine, in that it has plenty of torque. The 46 Plymouth car I would think, would be a heavier car than my little Coupe, so a different situation there. I believe the 46s may have 100hp, so with the right rear/trans upgrade for the LA area, a good running 100hp engine, would be good.... Quote Link to comment Share on other sites More sharing options...
Lumpy Posted July 3, 2014 Report Share Posted July 3, 2014 I used to fantasize about a straight eight, but it is too long for the six cylinder cars...two cylinders longer is quite a bit. (and Lumpy don't need it anyhow) Of course, it "could be done", but would require some really major and creative modifications...possibly more difficult than a V8, V6 or slant six swap. I certainly concur however, that if a six cylinder car is not going to fill the bill, selling the Coupe and finding a straight eight car would be a good option, rather than hacking up a car that many people would be delighted with just the way it is. Or, finding a V8 swap car that's already been done might be a good option. Having said all that, I still endorse, encourage the R10 swap. All things considered I think that's the path of least resistance, and least $$$$$. k. 1 Quote Link to comment Share on other sites More sharing options...
Tim Keith Posted July 4, 2014 Report Share Posted July 4, 2014 The R10 is out there... 1953 Plymouyh Dodge 218 Motor and Trans http://killeen.craigslist.org/pts/4539153168.html Quote Link to comment Share on other sites More sharing options...
st63 Posted July 4, 2014 Report Share Posted July 4, 2014 Wow, that's a great price! If the original poster doesn't jump on it, I might! Quote Link to comment Share on other sites More sharing options...
pflaming Posted July 4, 2014 Report Share Posted July 4, 2014 I checked freight: Freight to California is around $350. That is for a palletized shipment at $800#'s estimate. If closer very tempting, just mount in my 54 and 'bingo'. Could save a lot of work, yet never know what 'motor runs" means. Quote Link to comment Share on other sites More sharing options...
st63 Posted July 4, 2014 Report Share Posted July 4, 2014 That's not bad for shipping....and even if the motor itself isn't perfect, that tranny alone is worth the price. 1 Quote Link to comment Share on other sites More sharing options...
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