gzig5
Well-Known Member
See Post #30
340 Steel Crank
- Thread starter 67_Slimer
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Eagle I beam rods are around $400. Check with your machine shop how much they charge to recondition your stock rods with new ARP bolts. The engine build pros here can step in with piston suggestions.
As were the early 318 cranks, but the 273 and 318 forged cranks are different than the 340 cranks even though they are all neutral balanced. They get there differently. If you use the 273 or 318 cranks in the 340, the 340 really needs to be rebalanced.
And you will need lightweight pistons and rods. May be someone will know the weights of the 273 vs the 340 parts. You may run out of counterweights to drill to make it work.
FYI, remember the 273's used a heavy wrist pin to offset the smaller pistons compared to the 318. It would be fun to see what combo you would need to use a 273 crank in a 340. Heck, the 273 rods would be good to probably 450+ horse. The 400 horse 318 builds used stock rods. Same rod as the 273 uses.
Yup. I've always wanted to use the 273 rods in a hot 340. I've even got nice set I've held onto for years. I think with good rod bolts, they'll handle more. If you may remember, Mopar Performance sold a version of the 273 rods prepped with ARP rod bolts.And you will need lightweight pistons and rods. May be someone will know the weights of the 273 vs the 340 parts. You may run out of counterweights to drill to make it work.
There ya go! I didn't know about the MP rods. Mopar makes some tough engine parts. I can't remember the last time I saw a Mopar block windowed because of a broken rod.
I've "NEVER" seen a Mopar rod "just break". There was always something else afoot. Broken rod bolt, dropped valve and on and on. I've never seen a rod "just fail".
gzig5
Well-Known Member
I’ve got both 273 and 340 pistons and rods at home. Will try to weigh them later today. Interested in how the 273 compare to the Icon pistons and Scat rods I used in my 340.
The engine needs to be rebalanced regardless. As I said earlier, when I bought my 340 Dart, and tore it down later, it had a 318 truck crank in it.
Hell, just stroke it. Put a 4" crank and H-beam rods in it and go have fun.
Hell, just stroke it. Put a 4" crank and H-beam rods in it and go have fun.
With the lighter rods and some really light pistons, it would be a flingin little small block. May need some mallory metal in the counterweights of the crank, but it will need balancing anyway so what the heck?
I'll play ball: if you want to rev to the moon... Go with a 6.500 rod from Molnar, have the crank turned down to 2.10 journals and pick a 4" stroke piston to get the compression of your liking.
6.500 rods and a 3.31 sroke crank gives you a compression height of 1.445 with a 9.6 deck height. That is right around what most 4" stroker pistons come in at or a bit taller, and hey, the OG 340 pistons ran .018 above deck, why not you?
6.500 rods and a 3.31 sroke crank gives you a compression height of 1.445 with a 9.6 deck height. That is right around what most 4" stroker pistons come in at or a bit taller, and hey, the OG 340 pistons ran .018 above deck, why not you?
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Bingo!
If your going .060" a sonic check is a good idea. There are several 3.31" stroke oem cranks out there. 273 and 318, but the torque converter register will need to be opened up on the forged 273 crankshaft.
aaronk785
Well-Known Member
Scat I beams and a light weight piston and it will rev very well. I took my 340 with stock rods and 2316 pistons to 7000 for years. Never had any problems.
gzig5
Well-Known Member
Here’s what I have available to measure. It’s not a perfect apples to apples because some of the rods had bearings and some of the pistons did not have rings, but it is what it is and gives you an idea.
First two pictures are a 273 commando +.030” piston and rod and then the rod alone. Third picture is 30 over L 2316 340 piston and rod no rings no bearings. Last two pics are the standard bore stock 340 high compression pistons for my 71 340 with rod and then a rod alone
Not as much difference in the 273 vs 340 rods as I thought there might be. 42gram difference.
The information I have says that the +.020 Icon piston and scat rod combo that was used in my 340 weighed 1297grams. I don't have individual numbers for them at hand.
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Also,, check out the difference in the shape of the beam .
It is completely rounded on the edge of the side .
Tommy
It is completely rounded on the edge of the side .
Tommy
Now,,,compare the 340 rod to the rods in this picture .
The same shape on the sides, must be a Mopar thing .
The rods in this pic are both Mopar .
The big one is a factory 426 Hemi rod,,,the smaller one is a factory rod in my 291 DeSoto Hemi .
Both forged on the same shape and principles .
Tommy
The same shape on the sides, must be a Mopar thing .
The rods in this pic are both Mopar .
The big one is a factory 426 Hemi rod,,,the smaller one is a factory rod in my 291 DeSoto Hemi .
Both forged on the same shape and principles .
Tommy
As the MP racers say: Light is right...
NC Engine Builder
Grumpy Old Man
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Pretty interesting to notice the icon/scat 340 combo is SIGNIFICANTLY lighter than even the 273 combo, despite having a much larger piston. Plus the icons are forged, and the scats come equipped with arp bolts.
mayhem
Well-Known Member
This is where I would be.
67_Slimer
Real Hot Rods don't shift themselves.
So I ended up buying a virgin 340 Forged crank for $200. Looking to build a .060 11/1 street car motor that can hold its own against some of the new stuff lol. Hopefully a 55 year old crank can hold up. lol
cookietruck
Well-Known Member
Buy scat rods and the best heads you can..
67_Slimer
Real Hot Rods don't shift themselves.
As far as heads , I have out of the box Eddys on my current 340. Is there something else that would give a significant boost out of the box , unless its leaps and bounds ahead of what I currently have , I'll probably just use my current top end. Forged pistons are on my radar as well.
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