1972 Dodge Demon 340 restoration

[Whyjay]

Hello all, thought I should start a restoration thread for the 1972 Dodge Demon 340 my wife and I own. First the backstory on this car. It was our son’s high school car that we purchased in 1989. We bought it off a specialty car lot on South Broadway in Englewood, CO. It was sporting a bondo job in the rear quarters covered by a fresh E-5 paint job and painted on side stripes. But it was a true 340 car with matching numbers engine and transmission. We later sold the car when our son went off to college. A decision we always regretted.
Twenty years later I found the car listed on a website. The car was located in Arizona. I called the owner immediately and asked a few specific questions about the car to confirm it was the same one. He’d purchased the car in Colorado close to the person we had sold it to. Anyway here’s a few photos of the car in 2013 after purchasing it back.

 

[Whyjay]

The Demon was a great 20 footer. Closer inspection revealed the warts. It was still suffering from the rust repairs and cheap paint job from 1989 but still had the original engine and transmission- more on that later.
I addressed the immediate needs. New gas tank, rebuild the thermoquad, replace the leaking radiator and clean up under the hood and interior to make it presentable. It was a nice driver. The plan was to restore it soon but medical issues, retirement and a move to a more rural location came first.
Attached are a few photos from 2015.

 

[Whyjay]

For several years I’d been collecting the obvious needed AMD body parts but then Covid hit and plans were again paused. Moving on to late fall 2025 a friend and excellent body and paint guy had time to do some work on the Demon. Plans were to repair the lower quarters and drivers side lower fender. That quickly escalated once he dug into the old bodywork. Over the Christmas holidays we disassembled the car, carefully bagging and tagging parts, and delivered the car to Blast Tech.

 

[CFD244]

Awesome....Following

 

[Whyjay]

I’m so glad Adam, my body and paint expert, talked me into using Blast Tech. Getting the body down to bare metal exposed more rust damage and old repairs. I’m a bit short on photos to share but the attached gives a good representation of what he’s been working through.

 

[Whyjay]

These photos were taken last week. This week Adam was going to paint the bottom side of the car. We settled on a medium gray single stage matte finish trying to replicate the factory primer look. I don’t have any photos of that yet. Will post when I can.
OBTW I found an NOS left front fender to use. The original fender had lots of bondo holding the lower half together.

 

[Ramcharger360]

 

[glenn340]

Moving on to late fall 2025 a friend and excellent body and paint guy had time to do some work on the Demon.

Looks like your friend is doing a great job. You must be happy knowing it's getting done right.

I need to get me a body and paint friend...

 

[4spdragtop]

Very nice! Cool how it came back into your life! Gives you a chance for a redo and its gonna look amazing(IMO it did previously)

 

[mad dog]

nice job, im following

 

[Whyjay]

Meanwhile back in my barn workshop I’ve been busy. First up was the dash assembly. Following a complete disassembly I disassembled the instrument cluster, repaired the cracked and broken mounts in the plastic, cleaned all the gauges. The most time consuming part was prepping and painting the instrument cluster surround. A previous owner had sprayed the original wood grain facings a matte black which I covered with wood grain 3m decals after we got the car in 2013. Removing the decals exposed the remains of the ugly blackout attempt. I tried several methods to recreate the chrome details. I settled on using the Revell “ Chrom” spray paint. Hours of fun masking! I also used a chrome paint marker pen I found on Amazon for touch ups.
Meant to add the wood grain overlay came from DMT and the new harness from M&H via Year One.

 

[Whyjay]

Moving on to the dash frame there were a few dents to work out but overall it was in great condition. I prepped and painted it using the SEM black trim paint. Then I reassembled it all including a new dash harness and glove box insert.

 

[Builderguy]

NICE!!!!! I see in 2013 it was sporting a hood tach, I had one of those on a 69 RR and just loved it. Not super functional but it was a great look. IMHO
Are you planning on putting it back on?

 

[Whyjay]

NICE!!!!! I see in 2013 it was sporting a hood tach, I had one of those on a 69 RR and just loved it. Not super functional but it was a great look. IMHO
Are you planning on putting it back on?

Yes! It was on the car when we first bought it in 1989 but was non functional when we got the car back in 2013. I sent it off to have rebuilt around 2014. It’s going back on the car.

 

[DartManPlum340]

 

[Whyjay]

Moving on to a non-glamorous project. The heater box! Sorry I didn’t take more photos but I really wasn’t planning on this being such a PITA. The box had 54 years of dirt and leaves. A previous heater core replacement included a generous application of painters caulk that took hours of scraping and scrubbing to clean up.
I swear some previous owner used this car to hunt rabbits or prairie dogs by the condition of the front valance and bottoms of the k frame and oil pan. The “tell” was the hole in the front of the heater box covered by black duct tape. Looks like the muzzle of a rifle went through it. I repaired that with a epoxied metal backer and bondo filler. Didn’t try to hide it but it’s up out of sight.
The easy part took the longest. All new heaters cores should come with a warning label to fit check and bubble test before using. The first replacement heater core wouldn’t hold any pressure. Its replacement wasn’t much better providing a steady stream of bubbles. The third try came directly from the manufacturer ordered from one of the very few radiator shops still around.
Anyway it’s all back together and ready for installation.
Oh, the rebuild kit came from DMT. Very happy with the results.

 

[mygasser]

i know i say this a lot on here but you should consider painting both the back of the dash panel and the bulkhead area that's behind it in white. it won't show once it's all assembled but makes any future fault finding much easier as it'll be a lot brighter behind there.
neil.

 

[Big.J.007]

Cool build, following.

 

[4spdragtop]

Nice work, yep the heater cores can be a pain getting to fit as well.

 

[Builderguy]

Keep on trucking, and yes, DMT usually puts out very good products! Heater box looks very nice, well done Sir, well done indeed.

 

[Whyjay]

Moving along thought I’d share what’s going on with the 340. After doing a leak down test, with excellent readings- all eight cylinders less than 10% leak down, I was confident I could just clean it up, pull the pan to scrape off the generously applied orange RTV, check the oil pump pickup for debris and put it back together a prep for paint. That was the cheap me thinking.
After removing the original exhaust manifolds my suspicions grew. How come the exhaust ports weren’t matching the manifolds? Removed a valve cover and yup, someone had replaced the J heads with later model 318 heads. Ugh. With the heads removed I verified the cylinders were .030 over and had stock appearing replacement pistons (four valve reliefs and down in the hole approximately.060) plus tha couple cylinders had scrape marks like a pin clip had come loose.
So now the engine is at the machine shop. Hope it’ll clean up at .040 over. Piston pick is TBD but I’m considering a lighter weight ICON. Any thoughts appreciated.
The cam is an old comp cams 268H. To my eye it and the lifters looked fine. I’ll wait for the machinists opinion.

 

[crackedback]

Looks great, nice progress.

KB243's work for pistons. Find something that will give you a decent ratio with head CC volume and run it. Being at altitude is going to hamper performance a bit.

If you can find some J heads cheap, easy swap out. Can even do the cheater with 1.88's, have a good throat cut put on them and install a 2.02 valve if you want. Better working head than anything OEM put on these engines for that time period.

JMO, if the cam and lifters are in order and look good, run that old stick. It's a good driver camshaft and slightly bigger than a stock 340 cam IIRC.

 

[Whyjay]

I forgot to mention I found a pair of J heads that went along with the shortblock to the machine shop. I also had thought about 2.02 for the intake valves since the heads are bare and need everything. I’m going to discuss piston options once the machinists get to the engine.
At least it’s the numbers short block!
Coming soon: transmission, fun with the charcoal canister and repairing the grill.

 

[Whyjay]

On to the charcoal canister. I noticed a dribble of charcoal coming from the canister when moving it. Did some searching and found a couple write ups to use as a starting point.
Charcoal Canister Rebuild ????? Will this come apart????
And:
https://forums.ifsja.org/forum/tech-archives/engine/126342-vapor-canister-rebuild-a-new-how-to
Both helped but I still figured it out myself. To separate the base from the canister body I first wrapped blue tape as a guide. Using an abrasive cutoff wheel in my dremel I circumscribed a cut. I then used a fine tooth hacksaw blade to complete the cut. Note that I wasn’t quite prepared to separate the base and didn’t have the old cake tin ready to catch the charcoal some of which spilled out on the bench.
The base had remnants of a foam filter still attached. Also the bottom of the base had a replaceable fiberglass filter that looked to be the 54 year old original. Dumping the charcoal into a container I could see similar foam remnants inside the top of the canister. I was expecting to find metal mesh as per the 4BBO write up. Instead there’s a non-removable plastic “expanded waffle” providing a form of separation between the charcoal media and the external ports.
Knowing what I was dealing I came up with my plan. I ordered a replacement filter from the local parts store, then ordered 3 lbs. of activated charcoal and fine mesh stainless steel material Amazon.

 

[Whyjay]

My charcoal canister plan was to use the replaceable filter element (WIX 42998) both outside and top and bottom inside adding the wire mesh between the filters and the charcoal. Once the filter arrived I confirmed it also would fit inside the canister and order two more. I then cut the top and bottom stainless mesh filters including the small one for the center raised boss.
I fit checked then assembled the top filters into the cleaned canister using a bit of 3M spray adhesive to hold in place. Then the same process with the bottom. I then added the charcoal having previously measured the amount required (approximately 2 lbs.- basically full minus a bit). Finally I replaced the bottom using a thin bead of black RTV as an adhesive and sealant.
A side note the PCV valve is removable which being careful with 54 year old plastic I did. Be careful with the spring and metal cup the could fly away. The thin rubber diaphragm was dirty but intact. I cleaned everything and reinstalled the parts.
So that’s it. No drama but thought it was worth documenting.