Best thing to do with that 318 is to get a 408 stroker shortblock to put in its place.
If it is on one of the newer trucks the heads might be the same for the 318 as the 360. If not get a set of R/T heads that are ported.
To clear up a little confusion the 318 and 340 share the same stroke of 3.31" while the 360 has a 3.58" stroke.
While there are MANY different cranks available to change the stroke of a 318, two different approaches are commonly used and available.
First is to turn the mains down on a standard 360 crank, which costs about $100. This will give you around 350 cubic inches depending on the bore size. NORMALLY the deck height on a 318 LA engine is enough above the factory standard of 9.600 inches that you can use the Sealed Power 285NP cast pistons without modification. These pistons run about $90 from Summit.
The other commonly used route is to buy a 4" stroke crank marketed by Mopar Performance. The last price I saw from Summit was $349. This will yield around 390 cubic inches and will have torque in the neighborhood of a stock 440, a real stump puller. However, the pistons for this combo run over $500.
For either combination stock Magnum heads are the way to go in a 4X4 where you will not likely turn more than 5500 RPM on a regular basis. These heads will flow better than ANY previously manufactured stock Mopar small block heads, even better than the X heads. They also have an improved combustion chamber design with a size of 60cc-64cc depending upon manufacturing tolerances. Using them will require you to purchase different pushrods ($40) and different head bolts ($16). The intake manifold bolt pattern is also different and there are two approaches here. You can drill the heads for the standard bolt pattern which is really very easy or purchase an aftermarket intake for the Magnum heads. Depending on the camshaft profile chosen you might want new valvesprings but this is also a possibility with any heads used.
I have built both and each has it's drawbacks and advantages. Speedomotive.com also offers kits for 318 strokers.
I will tell you that a 360 will always give more torque and power for the same amount of investment but sometimes they are not easy or cheap to find. I will also tell you that sometimes it is just plain fun to be a little different.
You are welcome to contact me if you would like more info. I will be happy to help if I can.
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