Rod Length

[Jeff Rand]

I have been putting together a stage 2 for the past year. The crank was (UPS lost it) 3.625" and the rods are 6.3" (pin size is .927"), if I use my 3.54" crank, what length rod would I have to use to make the custom pistons work. I am not sure if there are other dimensions that one would need to complete the answer. This block has a short deck height of 9.413" Also would the change in the combo alter the compression ratio (8.75). I think the displacement would change slightly.
Thanks,
Jeff

 

[Mac in SD]

Jeff, how are ya'? I'd guess 6.385 length would get you back in the ballpark?

 

[Ron Tarabori]

Using your deck height and a 3.625 crank your pistons must have a pin height of 1.301. Using that with the other crank you would need a rod length of 6.342. Ron

 

[Mac in SD]

Ron, I thought I read that he's asking about the 3.54 inch crank.

 

[Jeff Rand]

Originally posted by Mac in SD
Jeff, how are ya'? I'd guess 6.385 length would get you back in the ballpark?

This is the number that I came up with but Neil Steward gave me the same number as Ron's.
Thanks,
Jeff

 

[Ron Tarabori]

I figured it in reverse. If the pistons were ordered for the 3.625 crank they must have a pin height of about 1.301. Then start with the deck height. 9.413 less the pin height of 1.301, then half of the stroke 1.770. 9.413-1.301=8.112. 8.112-1.770=6.342 rod length. Anyway your probably better off buying new pistons than changing rods. How did you get such a low deck. Thats over .120 off. Ron

 

[Chuck Leeper]

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Originally posted by Ron Tarabori
I figured it in reverse. If the pistons were ordered for the 3.625 crank they must have a pin height of about 1.301. Then start with the deck height. 9.413 less the pin height of 1.301, then half of the stroke 1.770. 9.413-1.301=8.112. 8.112-1.770=6.342 rod length. Anyway your probably better off buying new pistons than changing rods. How did you get such a low deck. Thats over .120 off. Ron

That short deck should make fitting an intake an "interesting process"

 

[Mac in SD]

Originally posted by Ron Tarabori
I figured it in reverse. If the pistons were ordered for the 3.625 crank they must have a pin height of about 1.301. Then start with the deck height. 9.413 less the pin height of 1.301, then half of the stroke 1.770. 9.413-1.301=8.112. 8.112-1.770=6.342 rod length. Anyway your probably better off buying new pistons than changing rods. How did you get such a low deck. Thats over .120 off. Ron

Doh! HALF the stroke! Me big dumb stupid.

 

[Jeff Rand]

Thanks for the info on the rod length. I think this is one of the Indy blocks that was decked to meet a certain cubic inch requirement. I had a BGC intake that was shaved .030" and the center end rails milled flat. The mock up with 1200 intake gaskets and stock head gaskets look good with the ports lining up. Also did a pressure test (used a leak down gauge) through the trottle body (25 psi) and it held without any leaks.
Thanks again,
Jeff