Big Block Chevy Small Journal Crank/Rods - Chevelle Tech

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post #1 of 7 (permalink) Old Mar 16th, 09, 12:39 PM Thread Starter
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Big Block Chevy Small Journal Crank/Rods

Can someone give me their opinion on why and when a Small Journal (2.10") rod and crank would be used in lieu of the standard 2.20" ? I have a set of Oliver Rods that are small journal.

Thanks

Tom B
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post #2 of 7 (permalink) Old Mar 16th, 09, 12:50 PM
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Re: Big Block Chevy Small Journal Crank/Rods

high rpm

In my opinion 7,500rpm and up but you may want to check with Mike AKA Wolfplace, Carl AKA CNCBlocks, Mark Jones AKA VORTECPRO and Tom AKA 3VPerformance

In small blocks above 7,500rpm i prefer the smaller rod journals (2" and less) over the larger rod journals (2.1").

With a good crank i dont see no durability issues however it may be a little different in a rat engine than a mouse engine - Check with those guys

Hope this helps
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post #3 of 7 (permalink) Old Mar 16th, 09, 1:17 PM
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Re: Big Block Chevy Small Journal Crank/Rods

I thought they used those to offset grind the crank throws for either a stroker or de-stroke application.
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post #4 of 7 (permalink) Old Mar 16th, 09, 5:55 PM
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Tim Smith
 
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Re: Big Block Chevy Small Journal Crank/Rods

'Bearing speed'


a 2" journal has a circumference of about 6.28, and at 7000 rpm the bearing sees (7000*6.28) inches of surface contact or 43,960" per minute.

a 2.1 has a circumf of 6.59, at 7000 rpm the contact is against 46,158"/minute.

about 5% less wear on the smaller of those 2.

Tim Smith
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post #5 of 7 (permalink) Old Mar 16th, 09, 6:42 PM
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Re: Big Block Chevy Small Journal Crank/Rods

Quote:
Originally Posted by oldtimr View Post
'Bearing speed'

a 2" journal has a circumference of about 6.28, and at 7000 rpm the bearing sees (7000*6.28) inches of surface contact or 43,960" per minute.
a 2.1 has a circumf of 6.59, at 7000 rpm the contact is against 46,158"/minute.
about 5% less wear on the smaller of those 2.

That's the way I understand it. Common in NASCAR.

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post #6 of 7 (permalink) Old Mar 16th, 09, 10:07 PM
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Re: Big Block Chevy Small Journal Crank/Rods

Main reason for small journal cranks is reduced bearing speed. Current BBC Pro Stock and Comp Eliminator cars are utilizing very small (Honda & Olds Quad 4) rod journals and 2.500 diameter mains (DCRE III block).
Another reason to use small rod journals is to enable the crank to be offset ground to either stroke or destroke the engine, as someone has pointed out in a previous post.

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post #7 of 7 (permalink) Old Mar 17th, 09, 1:41 PM Thread Starter
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Re: Big Block Chevy Small Journal Crank/Rods

Thanks !!!

Tom B
'71 540 Street/Strip Monte Carlo 10.310, @ 129.86, Pump Gas, Full Exhaust
'70 Chevelle, 462, 3.42's, 12.35, 1.66 60', 107.0 4020 lbs. Full exhaust Pump Gas
'87 Regal Limited Turbo T, Chip & Dual exhaust - 13.08, 1.78 60'
'75 Chevelle S3, 454, Auto (Son's Car)
2015 Tundra TRD Pro Supercharged 5.7
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