Dodge 318 upgrade


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Apr 17, 2023
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Hi all,

I got a ‘68 dodge monaco with a 318 on LPG gas. It did its job for about 23 years but now it starts stalling on idle, especially while braking and steering at the same time during parking or on an intersection.

I now want to start fixing but also upgrade everything a little. First thing is to upgrade the ignition for an electrical one.
1. What will be the best system to go with?
2. What leads would you recommend?

Next is to give it a little more power, as it gets slower and slower, but i first need to find a new gastank to make it run on petrol again.
3. What would be the first thing to give it some more spice? Intakemanifold? Carborator?

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I would put a vacuum gauge on it first and see if the motor appears healthy. I would also do a compression test. Assuming those check out, tell us what you have in there now for ignition.
You say it is getting slower and slower. I would address that first with the quick tests above before
spending money and replacing parts on a whim. Have you checked timing lately? When was the last tuneup? Is the diaphragm possibly an issue with the LPG fuel delivery? A little more info will help :)
As to the electronic ignition issue, you can either do an easy Pertronix-type conversion or go the normal route with a Chrysler-style OEM ignition kit, as Rick Ehrenberg sells on eBay from his store. He is an acknowledged Chrysler electronic ignition authority and has at least OEM-quality items, as the old Chrysler electronic ignition conversion kits used to be.

As to fuel delivery, petrol, new fuel tanks can be had from Van's or other places. Usually in the $300.00 range, plus shipping. Might need new fuel lines, too, for good measure, as the older steel lines are probably a bit rusty internally. A few threads in here on what started out being just a fresh fuel tank ended up being a full fuel supply system.

Then a Carter-brand mechanical fuel pump or a low-pressure electric pump. Holley has some new Sniper EFI kits to replace 2bbl carburetors. The original Carter BBD has the same base gasket size as a similar-sized Rochester 2bbl, so you can get everything in a kit for about $2500.00 USD or so. Then you will need a tank to match that system. I mention that option as you will need to replace everything in the fuel system. They offer a new distributor (an extra charge) to let the EFI system run both the fuel and ignition advance operations as a complete unit. So, that might be a decent option, other than for the cost of the kit and the labor to install it.

As to the engine itself, a Cloyes roller timing chain would ensure no issues in that area would appear for well past 100K+ miles. By the same token, a normal OEM set could do similar, possibly, but not normally well past that. Then leave the rest of the engine as it is, to your desires.

With the newer fuel system, you might desire to add a 4bbl intake and carburetor. A BASIC Edelbrock Performer intake would be a good choice (close to $375.00 USD for manifold and related gaskets). Main power improvements would be past 3000rpm, usually. Adding the 4bbl Sniper EFI would be operable. If no desire for EFI, then an Edelbrock AVS2 carb, about 550cfm would work with the 318 engine size.

I noted your location, so you might network with some of the other Chrysler C-body enthusiasts in the European region. As to sourcing and other things. In what I mentioned above, I was seeking to aim toward items more of an "add-on" or normal maintenance orientation, rather than getting into a complete rebuild situation.

Take care,
I would want to find out why the engine is going " slower and slower" before I did any modifications. Maybe it is in need of a rebuild. I agree with 65Port above.
I would want to find out why the engine is going " slower and slower" before I did any modifications. Maybe it is in need of a rebuild. I agree with 65Port above.

If the engine is getting worn out on LPG, it seems to me that switching back to gasoline before figuring out what's wrong could make things worse.

I don't know much about running on LPG, but I do know it's harder on valves and spark plugs. How long since you changed plugs? I'd do a compression test and better yet, a leak down test to establish what shape the engine is in now.
The '68 engine does not have hardened valve seats, a must for either propane or LPG. Run the compression check as noted above, I suspect you will find low compression on one or more cylinders is from burnt valves. LPG does not lubricate the valve train and the valve seats erode fairly quickly. Modern diesel trucks that have been converted to run on LPG run about a 10% blend of fuel oil to lubricate the top end of the engine.

Thank you all for the responses!
@CBODY67 will look into your options, sounds good! there will be a meeting with the chryslerclub september 1st, i’ll ask there too!

I already changed the plugs for new ones and cleaned the pins, that made it better but now back to the same. I want to change the leads too but don’t know which ones to get.
So the route to go is:
1. Replace leads anyway
2. Vacuum test
3. Compressiontest
4. Timing (anyone got a manual for me on how to?)
5. Clean LPG system
6. If all good go to LPG expert to tune

Anything else to tune/check?
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Chrysler factory service manuals can be found at , free download. Might need to choose a Plymouth manual over a Dodge of the same model year, sometimes.

Spark plug wires can be found at Standard Motor Parts has some good products which can be bought already assembled for particular engines, ready to install.

The issue of running natural gas instead of gasoline is very valid, as to exhaust valve seat recession/degrading and loosing compression.

Take care,