Best upgrade would be to sell that old motorhome and upgrade to a new modern motorhome with a better motor.
The truth emerges, at last!!!
Interesting discussion. My coach came with the 440-3 as did all FMC coaches. Most of them still run the 440 and the owners are quite happy with the power plant. These coaches are rear engined and so the radiators need to be kept clean to prevent overheating, but I have never heard of vapor lock as an issue.
The vapor lock issues discussed above are not an engine or carb problem, but an installation problem.
You can tell a 440 from a 413 very easily by looking at the exhaust manifolds. The 440 has the "log" type that bring the exhaust gas up and then together. The 413 manifold brings the exhaust gas slightly down and then together. The 413 also has better coolant flow through the heads and sodium filled valves. Both the 440 and 413 had valve rotators.
I don't want a new coach. My floor is 16 inches from the ground and very easy entry. The engine is in the rear so it is quiet up front. I have 4 wheel independent suspension. It is big enough for 2 people and small enough to go anywhere. I have to use cruise control to keep my speed down as it handles so well.
I am upgrading the engine from the 440, not because of a problem with it, but because I do want the torque of the diesel. So I am in the process of replacing the 440 with a GM 6.6L Duramax diesel coupled with a 6 speed Allison.
Note that the engine and transmission I am taking out has been purchased by a coach owner in Perth, Australia so it will continue in service. There are lots of units still out there running either the 413 or the 440 and parts are very available. This saying parts is an issue is nonsense for those of us that actually run these engines. I read about more parts issues for newer units than for my coach.
I was at a rally a few months ago where we had 16 coaches. Three had been converted to diesel engines and all the rest were still running the 440 and they were all happy with the engine and its performance.
FMC's are way cool, I would prefer the BBC powered one I inspected back in the late 80's, had a T-400 and GearVendors. Was surprised it was that way as I had only seen Chrysler power trains in them until this example showed up @ Capitol RV in Strudevent WI. However, 16 coaches doesn't sound like land rush numbers and old Mopar parts aren't all that common in most parts of the country. 20 years ago a local shop was unable to source brake parts for a Dodge motor home chassis, it was a Windybago, similar to the 413 powered unit I delt with once upon a time. Truth is your experience is typical for those dwelling in the SW, vehicles live longer out that way by far and parts support is in line with this reality. However I notice you modified your chassis with a GM produced engine and 6 speed Allison, guess that Mopar got old. I added a MD 3060 to my 3208 powered Wanderlodge last year, best modification one can do to a chassis. By the way now you can throw away that spare ignition resister that most Chryslers were famous for requiring. AND they must be pretty rare these days as a party down under had to spend a few bucks on shipping to source a power plant.
Best gas rig we ever had. ours had a Holly carb with external float bowel adjustments and cross over for the exhaust with glass packs. Would pull any hill, any boat, faster than any thing on the road. We got a steady 6.5 MPG no matter the load, the speed, the time of day, or the grade.
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We always carried a couple of spares for a quick change out.
By the way now you can throw away that spare ignition resister that most Chrysler's were famous for requiring. AND they must be pretty rare these days as a party down under had to spend a few bucks on shipping to source a power plant.