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Running smallblock rods in a big block engine??????

 
sparkplugless
I love my Chevy Chevette!
Posts: 5
Joined: 10/12
Posted: 10/21/12 03:25 PM

I was talking to a buddy today and he mentioned the guy who won points in the association that we pull trucks in is running smallblock rods in his big block.  i had never really heard much about this until now.  apparently he machined down the rod journals on his bbc crank to fit the small rods.  he claims that it gives a little more stroke out of your crankshaft, and it makes sense why.  plus there is less rotating mass to spin so you can build rpms faster.  has anybody else heard of this or done this?!?!?!  im wanting to build a new motor for next years pulling season and im really thinking about trying this.  any suggestions? anybody know how much more stroke you gain from doing this?  

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pepsi1
I mow my lawn and find Chevys
Posts: 1718
Joined: 09/11
Posted: 10/21/12 05:07 PM

He may have had a special crank made, with a small block rod journal. Then had special rods made up to get the length back. Then a piston would have to be made to except a small block pin.

Why would he do this? If it was really done I would have to see it. He spent a lot of money doing it. But why????

Bob  

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Dave632
I mow my lawn and find Chevys
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Posted: 10/21/12 06:04 PM

I once had BB rod journals OFFSET ground down to SB large journal size. This gave me a 1/8th inch longer stroke which resulted in a 468 coming in with about 482 inches. I used custom aluminum BB rods of the 6.535 variety.
I have never heard of using SB rods however. This would give you a very short rod and I would think the rod angularity would be severe. You would also need custom pistons and it would put the piston pin down on the piston. If you did NOT use custom pistons this would not work at all as that short rod would kill your compression ratio whereas the piston would not even be close to the top of the deck. As Bob said you could not use the BB piston pins either.
This is an old pro stock trick to slightly reduce friction and slightly
reduce rotating weight. This is also a way to save an otherwise good crank if one journal is scored badly. This setup worked fine and I had no trouble with any of the rod journals running N20 with up to a 400 shot. No bearing wear was shown.  
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ethelkilledfred-#001
I mow my lawn and find Chevys
Posts: 1371
Joined: 03/10
Posted: 10/21/12 10:33 PM

I think your mistaking rod journal size for rod type. We ran Honda rod journal BBC rods on a high rpm BBC Chevy with the crank cut down to Honda rod journal size. Too much bearing speed was the issue we trying to avoid. BBC rods are 6.135 and SBC rods are 5.7 giving you a difference of 0.435. You would have a piston almost 1/2 an inch in the hole. If you made a custom piston it would make the piston very heavy. This would not work anyway you try to make it work.  
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sparkplugless
I love my Chevy Chevette!
Posts: 5
Joined: 10/12
Posted: 11/17/12 08:16 AM

I asked more info...supposedly he is using a 6" aftermarket smallblock rod. he went to a swap meet and found a high $$ 454 crank that he paid almost $2000 for.  then he took it to a machine shop and had it offset ground for his rods. this is all i know.  i have personally seen this truck run....it is easily the best running truck in our pulling circut.  he won the points this year for the class that we pull in, and he also jumped up into the higher class and got like 3rd.  

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pepsi1
I mow my lawn and find Chevys
Posts: 1718
Joined: 09/11
Posted: 11/17/12 09:06 AM

It really sucks when you buy a high *** crank from a swap meet, then take and have the Nitriding removed from the bearing journals. He could have called Lunati and they would do anything he wanted, probably for a $2,000 he caold have had all the parts matched. Oh well it's not my ***
  Like Dave said the angle of the rod will wear parts at a very fast rate.
Thanks

Bob  

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tuffnuff
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Posts: 7841
Joined: 12/09
Posted: 11/17/12 09:14 AM

You may have the rod length all worked out, with offset journals and custom pistons.,. but what about rod width on the big end?
How much side clearance are you planning on running?
There will also be a balance issue, that needs to be dealt with.
None of this is cheap.
Good luck.

Smile  
When The Flag Drops.,.

tuffnuff

The Bull ***t Stops.,.
tuffnuff

P. Engineer, Engine Builder

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76Skylark
Big Block power for the win
Posts: 868
Joined: 12/11
Posted: 11/18/12 05:05 AM

The Man Must be doing it the way Dave did as there are to many other things to change any other way and as EKF said you can go smaller still with the Honda Diameter but the rod width(journal) has to be delt with.  

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redneckjoe69
I mow my lawn and find Chevys
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Posted: 11/18/12 05:21 AM

i suppose you could run a tig bead on both sides of the big end & have it machined back down to fit.  

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tuffnuff
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Joined: 12/09
Posted: 11/19/12 10:12 AM

Icon Quoteredneckjoe69:
i suppose you could run a tig bead on both sides of the big end & have it machined back down to fit.

More wasted money Joe.,. why not just go with the BB rods that have small Honda journals, that EKF suggested.

Smile  
When The Flag Drops.,.

tuffnuff

The Bull ***t Stops.,.
tuffnuff

P. Engineer, Engine Builder

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redneckjoe69
I mow my lawn and find Chevys
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Posted: 11/19/12 03:03 PM

true.  

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skyeking
I mow my lawn and find Chevys
Posts: 2738
Joined: 08/09
Posted: 11/22/12 02:58 PM

Hi Peter and Agent 69....
Yes I agree.
Why try to reinvent the wheel??
If the Engineers at Chevy thought that
a change was necessary to help the motor
and cut down production costs at the same
time it would have happened.
Full credit to you for researching the idea
before going any further.
A clear example of Instigation before an
Initiation..The excess of the idea has been validated.
 All the best from Skyeking...
All the best  
skyeking

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