Can a 318 crank and rods be used in a 340?

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rlofaro

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Hi All,

I have a 1970 4 speed duster that I am restoring. It is an original 340 car but came with a 318 in it. So I picked up a 69 block that I am ready to use. My question is:

Can I use the crankshaft from the 69 318 engine in my 340? Also can I use the connecting rods. The 318 was running when I took it out.
If it can be used, do I have to get it balanced for the 340 engine.
Thanks for all your help.
Richie
 
yes..they will fit ...as you said everything has to be balanced
 
Yes, the 318 crank will work... but with some caveats; we put a 273 cast crank in our 340. We won't be hammering on it so we felt the cast crank was adequate. You may have a cast or forged 318 crank; the forged will be stronger, but the cast is supposedly good for up to 400 HP or so.

The 318 rods are lighter than the 340 rods and will likely be weaker than the crank but again, it kinda depends on how you are using the engine. If you hammer on it at all, I would use something heavier or better. I am starting to favor the $300 SCAT I beam rods set; balanced right from the factory and good strength for an intermediate power engine with good rod bolts.

The 318 crank balance is set up for lighter pistons and rods than the 340 stock type. But, the exact answer to the new balance situation all depends on the new pistons and rods you use. If you use lighter hypereutectics pistons (like KB's), then the weight combo can end up lighter than the 318, and the shop will end up taking weight off of the crank (easy). If you use heavier 340 pistons like the Speed Pro's then you will end up heavier than the 318 combo; that is expensive to re-balance as you may have to add weight to the crank instead of taking it off.

So to answer your question, yes, you are almost certainly going to need to re-balance. How much that will cost depends on the rod and piston combo that you plan to use and that depends to some degree if you are going to have parts that produce more power than a stock 340. So you need to answer more questions before anyone can give a more complete answer.
 
Later model 318 rods are much stronger than pre 74. There is a comparison pic on here somewhere.
 
mguner said:
Later model 318 rods are much stronger than pre 74. There is a comparison pic on here somewhere.
Click to expand...

somewhere in the early 70s the 318 and 360 used the same rod...which is the same rod as the 340....
 
70aarcuda said:
somewhere in the early 70s the 318 and 360 used the same rod...which is the same rod as the 340....
Click to expand...

340's and older 318 also use floating piston pin, where as the 360 , and later 318's (with same rods) used a fixed pin, but either will work.
 
Thank you all so much for your input and knowledge everyone. Just wanted to see if I can save some money on the engine build. I am using the Upper half of this 318 which is a nice Eldelbrock Carb and Manifold and M/T covers. I just like to have a nice sounding engine, with some balls when you punch it. Growing up in the 60's and 70's, these 340 dusters either automatics or Manuals really were pretty potent right out of the factory in my opinion.
Thanks Richie
 
Hi Dano, I did not break down the 318 short block as of yet. So I do not know the cast numbers. It is an Original 69 engine and I assume it was never rebuilt. When I dissemble in a week or so, I will get back to you.
Thanks Richie
 
rlofaro said:
Thank you all so much for your input and knowledge everyone. Just wanted to see if I can save some money on the engine build. I am using the Upper half of this 318 which is a nice Eldelbrock Carb and Manifold and M/T covers. I just like to have a nice sounding engine, with some balls when you punch it. Growing up in the 60's and 70's, these 340 dusters either automatics or Manuals really were pretty potent right out of the factory in my opinion.
Thanks Richie
Click to expand...
It sounds like you will be happy with a 325-350-ish HP engine, and should be safe using the 318 crank.

Just as a comment for thought, if you use the lighter hyper pistons and lighter rods, you will end up taking off weight from the crank in the balance process and that is the cheap way to do it. That will be lighter on the parts and less stress if you do ever hammer on it. So that is one approach to consider.
 
That sounds great nm9stheham. Just want a decent rider, that cruises nice and looks and sounds good.
Thanks again for to all for the advice.
Richie
 
rlofaro said:
Hi All,

I have a 1970 4 speed duster that I am restoring. It is an original 340 car but came with a 318 in it. So I picked up a 69 block that I am ready to use. My question is:

Can I use the crankshaft from the 69 318 engine in my 340? Also can I use the connecting rods. The 318 was running when I took it out.
If it can be used, do I have to get it balanced for the 340 engine.
Thanks for all your help.
Richie
Click to expand...

yes they can
 
I always wanted to build a 340 using the 273 forged crank and the 273 rods. All that stuff is way lighter. Mopar Performance even offered the 273 rods as a performance piece for a long time, with good bolts. Those are tough to find now.
 
RustyRatRod said:
I always wanted to build a 340 using the 273 forged crank and the 273 rods. All that stuff is way lighter. Mopar Performance even offered the 273 rods as a performance piece for a long time, with good bolts. Those are tough to find now.
Click to expand...

Had 3 set of those at one time...MP sold them on ebay for 150 bucks a set...I sold all 3 sets to a board member....
 
I have 2 sets of the original 273 rods. Same rods, just not the MP style. Just stupidness I am hangin onto.
 
Wouldn't aftermarket rods be better stronger lighter and under $300
 
nm9stheham said:
Yes, the 318 crank will work... the forged will be stronger, but the cast is supposedly good for up to 400 HP or so.

The 318 rods are lighter than the 340 rods and will likely be weaker than the crank but again, it kinda depends on how you are using the engine.
Click to expand...

Just sayin.... I have seen cast crank engines live on the street and track in excess of 550 HP. But not a true serious street strip. It was one or the other. Like you said, it comes down to how hard you hammer the mill. And to that extent, nothing will live long if you hound the engine.

273 said:
Wouldn't aftermarket rods be better stronger lighter and under $300
Click to expand...

Depends on the rod. But mostly, yea. A good street rod isn't to expensive. A good race rod is. The stock rod is a very good forging. If there straight and do not require work to use, I'd go for it. (The beefier 340/360 rod)

What did did you have in mind?
 
Ford seemed to do well with cast cranks. My 340 has a cast crank. Unless your putting boost, NO2, or 10K rpm clutch drops to it, a cast crank can live a happy life when balanced and all the clearances are correct.

The Scat I-Beams for $360 are a bargain if your rods need any work and the Scat's come with ARP bolts so add that $70 to the cost of your stock rod resize.

In the end, I'd like to see what the OP has in the 318 to start with.
 
273 said:
Wouldn't aftermarket rods be better stronger lighter and under $300
Click to expand...

Sure, but the rods we're talkin about were produced LONG before you could buy something nice around every damned corner.

But to answer your question, in fact, no, there are scarce few rods that are as light as the 273 rods. In fact, there may not be any except for aluminum. That's why they were so popular. Prepped correctly and with good bolts installed, they are very strong.
 
Larry Shepard-the 273 - early 318 rod is 726 grams, I got 721 grams. Larry shepard-the 340- later 318 rod is 758 grams, I got 752 grams. I like blueprinted mopar rods with hi po bolts-made in USA. low priced aftermarket rods-made in china?-not so much. If U go with cheap aftermarket rods have them magnafluxed or zyglo or x-rayed tested before going high revs. I have never had a problem with tuned up 340 rods in 30 years to 7000 rpm
 
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