First build away from stock. Have a 46 Dodge deluxe coupe that the original flat 6 is done for. Car is very intact. All original still. Thinking of swapping in either a 318 or a 360. Would just like to change the drive train and rear. Keep the original front end intact but improve.. Can anyone point in the right direction for idea's and parts?
The front suspension isn't a terrible design on these. Just move the upper shock mount to the frame and add lowering springs & disc brakes. Not what you'd want for a high-speed road course, but plenty good enough for a cruiser. I would replace the rear axle, but I'm sure somebody else on here has more knowledge of it. I laugh at the guys who want to put an S10 ch***is under these. They have independent front/parallel leaf rear, just as this car does. You will probably have to offset the engine to the right to clear the steering box. Doesn't get much easier.
Stick with the flat 6. The 25” motors have more potential. Plus the big dodge trucks had a factory split exhaust. Very cool and no need to change too much.
I think your plan is great! That's such a nice car that it should remain stock looking outside and as you planned, just do the drivetrain. I'd suggest also swapping a newer rear axle, and an overdrive trans too so it's a fun car for trips or freeway cruising once you've got a late model V8 in it. If you own a good wire feed welder, then you don't need any kits. You can cut and fabricate motor and trans mounts easily. I've actually never bought engine/trans mounts for any V8 swap, and just made them from pieces of steel I have laying around, or s**** steel from the local steel supplier. If you don't own a Mig welder, now is the time to get one, as I think they're a necessity to do much fab work on any car build.
lots of info on the early mopar stuff, Tex Smith put out a how to book for example. I read the mopar small blocks were a good fit, the only real issue for street performance is the stock brakes. sounds like you are already on the right path.
Here's what I'd do: -Small block Mopar engine. -Whatever Mopar trans came with the engine; probably an automatic but maybe a stick if you can engineer the clutch linkage. -Ford 8" or 9" rear with stock Ford drum brakes. -Front disc brake kit. -Keep the steering, suspension, body & interior stock. Then drive it!
I like the small block idea myself maybe even use a Magnum 5.2 or 5.9 with an aluminum intake and carb or EFI. If I remember correctly both engines were around 300 hp and got decent fuel mileage, you could use the OD transmission and either a 8.25 or 8.75 mopar axle with a 3.25 or 3.55 gear. This would give you smooth performance and great highway cruising. edit: you can use the rear disk brakes from a Jeep liberty on either axle ***embly, they bolt on like the backing plates of drum brakes.
I've had a few Mopars of this era, let me tell you what I've done with a few of them many years ago. The front suspension on these Mopar cars was well ahead of all the other car companies at the time. First off, all the 46-48 Mopar produce line has the same suspension parts, the parts interchange across the Chrysler brand. Your front suspension made its entry into the world with a 39 Plymouth, and carried on into the early 50s with minor modifications. Several regular auto parts stores (as of 2 years ago) can still get most of the suspension parts. Years ago, when I was dealing with these cars a lot, www.robertsmotorparts.com was a good outlet if you can't find original suspension (or need other original/repop) parts. Moving the upper shock mount from the upper control arm to a bracket on the frame removes most of the "floating on air" feeling that was popular when the cars were first built. That one change makes the cars feel more modern through more stable handling, takes that mushey feeling away, without drastically making the ride more rough. Those upper shock brackets are not hard to make if you have any fabrication skills or I believe the upper bolt on shock brackets from the early Ford pickups are still available. More improved handling can be gained by adapting a front sway bar from modern Jeeps. Many of this era Mopars did not even have a front sway bar. I believe the sway bar was optional, if you car has a sway bar, its likely to be very small diameter, the Jeep bar swap is an improvement from the OEM unit, and you should be able to use the OEM sway bar mounts with the Jeep bar, or the Jeep bar mounting hardware can be modified to fit your Dodge. If you choose to lower the front end a couple inches, the front spring sits on a pocket that is riveted to the lower control arm. On the earlier models, that spring pocket was riveted to the top side of the lower control arm. Once the rivets have been removed, that pocket can be moved to under the control arm, then the rivets can be replaced with 4 grade 8 bolts and lock nuts (No longer remember the bolt size, or what year Mopar moved the spring bracket to under the control arm). If your front springs are bad, you can use Ford Areostar minivan front springs as replacement, those will drop the front a bit too. There were several companies that produced disc brake conversion kits, some more complete then others. I don't know which companies are still producing those kits, but if you find a kit you like, that does not list your Dodge (or the 46-48 any make Mopar) call them and ask most ads do not list everything they have available. A small block Mopar is a good choice for these cars. Plan on offsetting the motor & trans towards the right side (the p***enger side in the USA) about 1 1/2" from center. That provides steering column to exhaust manifold clearance problems, one of the biggest challenges to this swap. Offsetting the motor eliminates the need for any specific exhaust manifolds. I suggest you remove your inner fenders before you begin, that will make the entire job easier. You can modify the inner fenders and install them afterwards, if you choose. You will want motor mounts that can be welded to the sides of the frame rails. I suggest you hang the motor & trans into place, carb base as level as possible in all directions, then mark any clearance issues. A few to look for: I have run into a few cars where the bottom of the crank belt pulley runs very close to the front frame crossmember. With those, I have cut a notch out of the cross member, for pulley clearance (and to easy belt replacement), then boxed the area back in (if done carefully, you can flip the piece you cut out and pretty much weld it back in). On the Mopar small blocks, the right side head sets farther back then any other part of the motor. Often the area to the p***enger side of the car (USA version) of the firewall past the original firewall "dip" needs a bit of m***aging with a hammer to provide ample clearance for the head. Basically, you need to extend the original "dip" about 6" toward the p***enger side and about 6" high above the area where the firewall angles towards the back, about 1/2 the depth of the original dip (about an inch deep). Expect to modify the inner fenders. Remove them to place the motor, then modify them to fit back in after the motor runs and drives. I have run several cars without inner fenders with no problem. The Magnum small block (5.2 or 5.9) occupies about the same amount of space in the engine compartment. The wider serpentine belt may require a bit more front crossmember clearance. The Magnum motor is a pretty big jump up in HP over the older LA motor in their original form, but if you are rebuilding the motor, that advantage can be mostly eliminated. The Magnum heads have the best flow rate of any Mopar small block (the 5.2 and the 5.9 Magnum use the sameheads), but those heads do have some issues, do your research. You are going to have to fabricate a transmission crossmember. I believe the center X on the frame was gone by 48, but if you car still has the center X in the frame, you may need to modify the center of the "X" for transmission (especially of you are using a Mopar OD trans) and drive shaft clearance. No need to be too concerned about the change in the drive shaft angle, the change is well with in the U joints capacity, I have never had an issue with the U joints in one of these swaps. As far as the rear ends, the original rear end has those tapered axles that can make checking the brakes a long project, and really doesn't offer many gear choices. Be aware that your original leaf springs are an inch narrower then modern leaf springs, changing the springs requires changing the spring mounting brackets as well. A "bolt in" modern rear axle will probably require changing the axle's spring mount perches to the older narrow brackets, or creative shock plate/U bolt installation. Modern, easy to find rear end choices that can mostly bolt in area: 1) A Jeep 8 3/8" (formally called an 8 1/4) is about the correct width and has the same wheel bolt pattern as your original rear has. It would be tough enough for some abuse, or years of normal driving. there are a few gear choices offered with the Jeep rear end, and drum or disc brakes were offered (I believe). 2) A Ford 8.8 from an Explorer. The width is about right and the bolt pattern is the same as your original rear end. They were offered with several gear choices, and as drum or disc brakes. The Ford rear end also has about the same offset as you are placing the motor/trans in. If you car still has that center "X" in the frame, the entire "X" may have to be removed. With either rear end choice, you will need to pay attention to the wheel offset, the wheel width, and your tire choice for fender clearance. The choice between the LA small block, or the Magnum small block, the choice between a carb & electronic / points ignition, or EFI, the manual transmission (with or with out OD) or the automatic transmission (with or with out OD) are all a personal choice. The LA motor may be easier to do with the carb, the Magnum may be easier to do with the EFI, but the EFI may require a fuel tank with an electric fuel pump in it. My current 48 Plymouth business coupe (built in 2011) has an LA 3.9 EFI motor (obd1) with a 5 speed OD and 3:55 limited slip rear. The old Plymouth was in very rough condition (its on a 90 Dakota frame because the original frame had huge rust holes in it) and looks like an old dirt track car. A 3.9 v6 is a 318 with 2 cylinders cut off. That V6 hauls the car around pretty well, the 3.9 was also available as a Magnum motor (with OBD 2). The magnum motor has 30 hp more then the LA version, factory rating, both box stock. I did have a 3.9 V6, 2bbl carb, electronic ignition, backed with an OD auto trans and a 3:55 rear gear, that car was respectable to drive as well, the 3.9 is another option with a smaller foot print, if you find one, rebuild costs are about the same as an LA 318 or 360. If gas mileage is a concern, generally not babbied: A 3.9 V6 (LA) will pull 22 mph on the highway, 17 mpg in town (5 speed, 3:55 gears but the OD auto is close). A 318 (LA) pulls 20 mpg highway, 14 in town (auto OD, 3:55 gears). A 360 (LA) pulls 14-16 mpg highway (driven carefully) 10-11 in town (auto OD, 3:55 gears). Your mileage may be different. My 48 Plymouth coupe. Driven 88,000 miles through 27 states since 2011.
@gene-koning has it all laid out for you! I used the book shown earlier and tips from here on my 40 Plymouth. I didn't offset quite as much and it required A body exhaust manifolds to clear the steering column. I also kept the firewall as-is and it will require an electric pusher fan (not the best.) It's a 92 318 magnum with auto OD non-lockup. I still haven't finished it though so can't comment on how well it all works. I used a 1968 Dodge B body 8.75 rear axle, but stuff like that is getting harder to find in good shape cheap. Since it does not fit HAMB timeline, I won't post pics here. You can see some in my album. https://www.jalopyjournal.com/forum/media/albums/project-1940.131/\ There were a few builds similar to this over the years. I'd suggest doing searches for more detail, but Gene covered all the important points. If you end up going with a flathead 6, I would go with the upgrade to front suspension (shocks, sway bar), rear axle (better brakes, axles and gear ratios) and if you can research and grab the bits, a 5 speed. They aren't big HP motors, but do make good torque, so you just need to keep it in the powerband.The forum for P-15 D-24 will be useful if you go that way. For all the rest of the car they cover things well, too. Check the tech section for basics. https://p15-d24.com/ I don't care for wheel bolts, so the non-energized brakes were a must-do for me.
I recently finished a '40 Plymouth for a guy. Pretty much the same car before and after the war. I agree with all the above, the front suspension is great, rebuild kits are readily available. I adapted a Saab 2003-2006 power rack and pinion so I could squeeze in a 331 hemi and 200R4 OD ******. I added a Mustang rear end. All went together pretty easily. Biggest problem was squeezing tubing headers in between frame and engine!
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