340 Nodular or 318 steel crankshaft

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southerneagle

southerneagle

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I'm building a 72 model 340 and I have both,(340 Nodular and 318 steel) the 340 has never been turned and mic's out as to only needs to be polished, the 318 needs to be turned 10 on the mains and 10 on the rods...This is going to be a street beater and I don't think it will see any drag strip action. I have a set of J-heads to go on it and I planing on a hughes whiplash cam, it is going in a 72 Dart with a 4 speed.Which one should be better for me? Thanks!
 
Go with the steel crank vs the cast crank. Might want to make it internal balance over the external balance.
 
Nodular iron is a very strong metal, steel is even stronger lb per lb (they are so close metalurgically speaking) . The 318 steel crank has solid throws, the 340 nodular has lightened throws (to compensate for the heavier rods) so it will be lighter in the long run if you plan to use 318 rods. You always want to remove material to balance, much cheaper than adding tungsten. You are going to balance the 318 crank @ about $175 so I would stick with the 340 just as a cost measure if your not going to flog it. Keep balancer of 340, unique.
 
Can I use the 340 rods with the 318 crank?? I was told the two are basicly the same is that true as well? I don't mind spending the money to have the 318 crank balanced if that would be a better way to go. What about the flywheel is it different between the two? Thanks again
 
you can use either rod with either crank...just needs to be balanced along with the pistons..
 
The steel crank MAY be easier to balance and would be internally balanced as well. Easier to find a neutral balance flywheel.

If you already have the balancer and flywheel for the external balance 340 cast crank, run that. The cast cranks are pretty tough.

IMO, street beater, run the the most cost effective unit you can put together. A 400hp 340 doesn't NEED a forged crank.
 
the way I understand it is that a steel 318 crank would be from around 66-67. It could have a 1.55" pilot bushing hole at the back of the crank for the torque converter. Most all converters on the market are for the later larger hole 1.8".

Check this out! It could save you a headache down the road. If it has the smaller hole, have a machine shop put it on a lathe and make it the bigger size.

good luck with your build!
 
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