6" rods on crank made for 5.7" - Hot Rod Forum : Hotrodders Bulletin Board
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Old 12-24-2008, 11:32 AM
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6" rods on crank made for 5.7"

I found killer deals on brand new SBC crank and rods so I bought them. The crank is a 1-piece rear 3.75" 4130 forged stroker, and the rods are 6" H-beam 4340 forgings.

After investigating it, the crank is made for 5.7" rods. Is the only difference the target bobweight? If so, what would be involved with balancing it for the 6" rods? I mildly prefer the 6" rod length, but if its too involved or to expensive I'll sell them and buy 5.7s

Can someone walk me through some beginner tech of rotating balance?

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Old 12-24-2008, 02:01 PM
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The extra rod length will make no difference in the balance job aside from a possible minor bit of extra weight.
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Old 12-24-2008, 02:12 PM
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Quote:
Originally Posted by curtis73
I found killer deals on brand new SBC crank and rods so I bought them. The crank is a 1-piece rear 3.75" 4130 forged stroker, and the rods are 6" H-beam 4340 forgings.

After investigating it, the crank is made for 5.7" rods. Is the only difference the target bobweight? If so, what would be involved with balancing it for the 6" rods? I mildly prefer the 6" rod length, but if its too involved or to expensive I'll sell them and buy 5.7s

Can someone walk me through some beginner tech of rotating balance?
The counter weights are shorter on the because of the 5.7 and going to a 6 inch rod will give you more clearane when the piston is a BDC. most 6 inch rod cranks will take a heavier bob weight.

And the crank will be lighter as well as we buy all our cranks machined for 5.7 rods.

You can't use a 6 inch rod crank with a 5.7 rod!!!
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Old 12-24-2008, 02:28 PM
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But I can use a 6" rod with a 5.7 crank?

I'm either going to use this setup in one of a few 1-piece blocks I have or sell it for a wee profit. Seems like no one will buy the setup because its a 5.7 crank and a 6" rod.

What do I tell them to prove that its OK to use them together?

I guess more importantly; why do they sell a separate crank for different rod lengths if it doesn't make that much difference?
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Old 12-24-2008, 03:18 PM
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Quote:
Originally Posted by curtis73
But I can use a 6" rod with a 5.7 crank?

I'm either going to use this setup in one of a few 1-piece blocks I have or sell it for a wee profit. Seems like no one will buy the setup because its a 5.7 crank and a 6" rod.

What do I tell them to prove that its OK to use them together?

I guess more importantly; why do they sell a separate crank for different rod lengths if it doesn't make that much difference?
Yes you can use a 6 inch rod with a 5.7 rod crank and 6 inch rods crank are common with 383's withthe bigger counter weight you can internally balance the assembley.
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Old 12-24-2008, 04:56 PM
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Sweet. Thanks for the info. Now I'm off to measure my decks to see how much compression height I can get away with

I actually knew what I was doing all along, I was just testing you guys *cough*
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Old 12-24-2008, 06:45 PM
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Internal balance also adds a little stealth to your displacement. to roaming eyes.
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Old 12-24-2008, 07:14 PM
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Mmmm... stealth.

My first choice would be to stroke my LT1. I have a set of heads ready to port and all estimates point to 420 hp. I also have a Vortec longblock at home that is itching for a home in a truck that I haven't bought yet

I also have a Vortec 350 in my boat that might benefit from the extra cubes.

But I also have some attractive offers to buy the set for more than I paid, so I'll have to look at the Christmas bills to decide what route I take.
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Old 12-28-2008, 12:14 PM
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Assuming a 9" deck the comp height will be 1.125
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