440 or 318

I'm in a dilema. Need someones insight. I have a 1980 dodge half ton 4x4 pickup and am needing more power. The truck has a propane conversion and I'm wondering if it would be smart to put some money into rebuilding the 318 that is in it. Upgrading the cam to something to give it a bit more torque or I have a chance at buying a 440 with a propane conversion. I would like to keep it on propane because of the cost factor and am wondering if the 440 will be a hog on fuel compared to the 318. It is a heavy truck with big tires and needs some more torque to make me happy. Any input would be great. Thanks  

318 vs. 440, thats like comparing apples and oranges.
318 is economical and the 440 is a torque monster, just what a big 4x4 truck would need. However it will get half the fuel economy of the 318.
Solution, a 360 will bolt right up to your trans. many of the parts are interchangable with the 318. It will still get decent fuel economy and the longer stroke of the engine will make moving the big truck that much easier.
Just my two cents.  
Doc  

would i be able to use the 318 heads on the 360 since the exhuast valves have been coated for use with propane. If not is the coating of the valve absolutely nessesary. The 318 i have isn't all that economical because i have to have the pedal to the floorboards even on the slightest inclines. It just doesn't have the torque to pack such a heavy load.  

318 heads will do nothing but hurt the performance of a 360. I am not certain about the exhaust valve size of a 318 so I cannot answer the second part of the question, sorry.
 

Or stroke the 318 to 390 w/360 heads, get a lil better gas then the 440, and still make mucho torque.  
age is no lock on brillance

Before you go to swapping engines.  What gear ratio are you running.  A set of 4:10 gears may be all you need. Just my two cents.  

also what size tires if your running 44in tires you would need even more gear.
the propain gets about half the milage pergallon as gasoline so is it truly worth the propane for the cost  

Ok.. my couple cents worth...

1)  Propane has significantly less energy content than gasoline... on the mid 60s farm tractors it was a reduction in hp of about 20% over the gas or diesel counterparts. So I expect that 318 is a bit sluggish to start with and its installed in a 5200 lb or so vehicle... yea, I expect it can't get out of its own shadow...  (I have a stock '86 318 W150 4spd... can't get out of its shadow either and its stock sized on tires)

2)  Gearing.... big time necessity when running over sized tires...  given number 1 and if its running stock 3:33 (or so) 4x4 gears with over size tires... your continuous over working it... just doesn't have it.  Think about the changes in circumference and how much ground it covers in one revolution at the ground... back calc that up through your drive line.  You may be surprised how the torque dynamics change.  Remember... you drive torque not hp.  Only on the track at very high rpms do you "drive" hp.

3)  I do not know what propane is costing where you are, but its real expensive where I am... for me... a stroke kit 318 or a 360 along with higher ratio gears (4:10 or even more if your running really big tires) will get a bit of performance in it and since it will not be over working the engine all the time, you'll likely double you dollar mileage over your current situation.  And... its a simple bolt in.   What the high perf guys are getting out of mildly warm 360 is impressive (370-400 hp, about the same torque).  Much more if they get real serious.  Cam and head it for torque and I think you'd have a good match along with 4:10s or what ever you need to match you tires.  You want the same trans output rpm (or even a little bit more) at the same mph as stock to compensate for the tire's change in circumference.

4) Yea the 440 will make it go (gas or propane)... but you'd still need the gear change and it will be much thirstier at cruise.  Its also a lot more work to swap in in.  Id opt for a stronger than stock A block and gears I believe for a daily driver.  If your after bragging rights and can afford it, work up the 440... but you'll have to beef up the trans, transfer case and axles too... getting serious on the 440 with the foot feed on a small block drive line will start twisting things... like input shafts to the diffs, axle shafts etc. A hot 360 will too.  Thus the "mild" warming I mentioned.

Dave  

Dont get a 360, a 318 is a way better motor than a 360. well in my experience anyway. there was a 360 in my 74 Satellite and it sucked gas and had no power at all. We put a 440 in and it gets way better fuel economy and way more power. and 318s are fantastic motors and would get better economy but if you reaelly wanna push that truck there's nothin like a big block.  
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1974 Plymouth Satellite Sebring Sundance, 440cid, 727A.