Forged 340 Crank in a 5.9 Magnum

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KS Hcode

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I have looked and looked and cannot find the answer. Probably because I am too new around here...

I have a forged 340 crank, forged Hbeam rods and some JE SRP standard bore (4.04) pistons. Since it is next to impossible for me to find a good 340 block near me, I was wondering how feasible it would be to drop the 340 rotating assembly into a 5.9 magnum with the appropriate crank bearing spacers?

If I wasn't going 4 speed then I would not bother with the 340 crank. Also I know the wrist pin locations are different on the pistons so I could not just plug in the rods and pistons.... Unless I am missing something.

T I A,
Dustin
 
KS Hcode said:
I have looked and looked and cannot find the answer. Probably because I am too new around here...

I have a forged 340 crank, forged Hbeam rods and some JE SRP standard bore (4.04) pistons. Since it is next to impossible for me to find a good 340 block near me, I was wondering how feasible it would be to drop the 340 rotating assembly into a 5.9 magnum with the appropriate crank bearing spacers?

If I wasn't going 4 speed then I would not bother with the 340 crank. Also I know the wrist pin locations are different on the pistons so I could not just plug in the rods and pistons.... Unless I am missing something.

T I A,
Dustin
Click to expand...
What is the compression height of your pistons, or the part number?
I have a set of SRP pistons I plan to use in a Magnum block. I think they are part number 34796 with 1.670” compression height. We still had room to deck the block to get close to zero deck with these.

Search for threads on four speed swaps with Magnum 360 engines. I know there was few asking about that. As long as you are not using factory Magnum fuel injection a four speed swap should not be too bad.
 
Bob,

Yes my SRP's are 1.670 CH. I plan on going the 6pack route as that is what my dad had in his car. Hoping I can make it all work out the way I have it in my head.
 
Bobzilla said:
What is the compression height of your pistons, or the part number?
I have a set of SRP pistons I plan to use in a Magnum block. I think they are part number 34796 with 1.670” compression height. We still had room to deck the block to get close to zero deck with these.

Search for threads on four speed swaps with Magnum 360 engines. I know there was few asking about that. As long as you are not using factory Magnum fuel injection a four speed swap should not be too bad.
Click to expand...
Were you using the factory 360 crank?
 
Just use the magnum 360 crank. You won’t make enough power NA to hurt it I promise.
Sell the 340 forged crank to someone who’s restoring something and will pay big bucks for it.
 
By use of my calipers and not a mic, have not invested in a set yet, my wrist pin is .984, from top of piston to top of wp hole is 1.182. That would give me the 1.674 CH. If using 6.123 rods then would 6.123+1.674CH+1.79(half stroke) equal 9.587 which would be just under the 9.6 deck height?
 
TT5.9mag said:
Just use the magnum 360 crank. You won’t make enough power NA to hurt it I promise.
Sell the 340 forged crank to someone who’s restoring something and will pay big bucks for it.
Click to expand...
And how much $ am I going to be out in machine work to get the 360 magnum crank to be ready for an 833?
 
KS Hcode said:
So it is a direct fit with no machining? That makes life easy.
Click to expand...
This one is for a T56 magnum but you get the idea. No machine work necessary.
20D0C9F5-945E-4A87-9520-D149A4106BB2.jpeg
 
Awesome, thank you for this. Also, what are the lines that have a T going to the heads? Extra oiling for the LA heads on a Magnum block?
 
KS Hcode said:
By use of my calipers and not a mic, have not invested in a set yet, my wrist pin is .984, from top of piston to top of wp hole is 1.182. That would give me the 1.674 CH. If using 6.123 rods then would 6.123+1.674CH+1.79(half stroke) equal 9.587 which would be just under the 9.6
Click to expand...
Well 6.123 + 1.674 + .179 equals 7.976, which will leave you a full 1.624 BELOW deck, figuring a nominal deck height of 9.600
 
Your 1.79 is half a 360 stroke, but you said you had a 340 crank correct? Half of that stroke is 1.655. So it still doesn't work out for you
 
KS Hcode said:
Awesome, thank you for this. Also, what are the lines that have a T going to the heads? Extra oiling for the LA heads on a Magnum block?
Click to expand...
Yes exactly. I’m running W2 race heads on a magnum bottom end, oiling them externally in to the rocker shaft stand and via the pushrods.
 
replicaracer43 said:
But it's late, my brain is fried, and my math and memory might be off!
Click to expand...
Understood. I do have a forged 340 crank. I was just seeing if it was feasible with the bearing spacers. But since the piston math does not add up, you were right above, then I should sell the crank and use the stock 5.9 crank.
 
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