BBC Connecting Rod Question - Chevelle Tech
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  #1  
Old Nov 19th, 09, 3:46 PM
Stokerboats Stokerboats is offline
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Dan
 
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Default BBC Connecting Rod Question

Chevy produced several Rods for the Big Block. The two in question follow; How do the "thumb" truck rods compare in strength to the dimple rods used on the LS6&7? Realizing the rod bolts are 3/8 and 7/16 respectively. Thanks, Dan
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  #2  
Old Nov 19th, 09, 5:56 PM
GRUMPYVETTE GRUMPYVETTE is offline
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Default Re: BBC Connecting Rod Question

the typical stock chevy rods weak point is the rod bolts that may stretch or caps, held by the rod bolts, the BETTER ARP rod bolts (L19 )are typically at a minimum 50%-100% stronger,than the stock bolts, if the same diam. is used, going from a 3/8" diam. to a 7/16" diam. adds about a 18% additional cross sectional area, significantly adding to the strength, but its rather silly to refurbish the stock 3/8" bolt BBC rods, in my experiences building BBC engines ,when there are far stronger aftermarket rods already built with ARP cap screw rod bolts and made from 4340 forged steel that cost about the same as all the work typically costs to bush,the small ends, refurbish,the rods,add ARP fasteners, polish, balance those rods and still have an inferior, and weaker rod.


http://www.adperformance.com/index.p...78642e07cca44d
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  #3  
Old Nov 19th, 09, 7:48 PM
bcmiller bcmiller is offline
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Default Re: BBC Connecting Rod Question

Dan,

You can go to this "sticky" for more information. I think there is something in there about that.

http://www.chevelles.com/forums/showthread.php?t=214916

Stock rods are OK for normal/stock use. Once you get to higher performance, aftermarket rods are probably needed. Thumb rods probably are not as strong as the dimple rods, and the dimple rods are not as strong as aftermarket rods - in most cases.

But like Paul said, the price on the aftermarket rods is so reasonable now, sometimes it doesn't make sense to recondition old rods.
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Last edited by bcmiller; Nov 19th, 09 at 10:09 PM.
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  #4  
Old Nov 20th, 09, 1:03 AM
Stokerboats Stokerboats is offline
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Default Re: BBC Connecting Rod Question

Thanks for the replies. I'm fully aware of the fact that some aftermarket rods are a better choice than the chevy stuff but that being said years went by where chevy was the choice. It is not always the case that aftermarket rods are better and it is not always the case that resizing and upgrading rod bolts is neccessarily a bad thing. I've seen some pretty heavy abuse on factory rods (nitrous runs included) without an issue of reliability. Are high quality aftermarket rods better? YES but cheap chinese stuff isn't always what it is advertised to be.
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  #5  
Old Nov 20th, 09, 1:13 AM
Harold Sutton Harold Sutton is offline
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Default Re: BBC Connecting Rod Question

I've never broken a Chevy "high performance" rod, ever. I've seen lots of aftermarket rods break, mostly rod bolt failures. The lesser Chevy rods aren't nearly as strong, but all the high performance rods are very strong. I knew an old time Chevy racer state that the 3/8" rods were stronger than the 7/16" rods because there was more material in the weakest part of the rod than the bigger bolt ones where the bolt passed through.
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  #6  
Old Nov 20th, 09, 5:46 AM
71454Chevelle 71454Chevelle is offline
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Default Re: BBC Connecting Rod Question

What material (4340??) are Chevy rods? Are all OEM rods made from the same material?
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  #7  
Old Nov 20th, 09, 6:35 AM
ToyzRMe ToyzRMe is offline
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Default Re: BBC Connecting Rod Question

If I'm redoing stock rods, I use these. http://www.summitracing.com/parts/AR...1/?image=large

These are sooooo much better than rod bolts with a knurled shank, and easier on the rod bolt bore.

That being said, till you add the price of these bolts and the cost of resizing, straightening, and balancing a set of stock rods, the best value out there, IMO, is these. http://www.summitracing.com/parts/SC...6/?image=large

You can buy these from Flatlander Racing for $299.00. Well worth the price, as these are really nice, stout rods. http://www.flatlanderracing.com/


Randy
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  #8  
Old Nov 20th, 09, 7:28 AM
forcd ind forcd ind is offline
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Default Re: BBC Connecting Rod Question

when i built my "budget" 496, i used a cast Scat crank, stock truck rods, and Wiesco pistons designed for the stock rod length-i decided on the truck rods because i had them and fig in the price of rebuild and new bolts comp. to aftermarket
even if i bought cheap aftremarket, i would still need them ck'ed to be safe
the 7/16 BB rods seemed to vary a lot, right at the part line, you could almost see the bolt on some, part of the reason some fav. the truck rods with 3/8" bolts
on the average performance engine, if built right, i dont think you would see a rod problem
i ran truck rods on a blown 454 for 8 years, a few 1/4 passes every year, nothing really high dollar, they were perfect when the engine was pulled apart
In todays world, esp street stuff, there is a lot of over kill on parts, not a bad thing, but
you can get by with less
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  #9  
Old Nov 20th, 09, 7:56 AM
Busted Knuckles Busted Knuckles is offline
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Default Re: BBC Connecting Rod Question

Quote:
Originally Posted by Harold Sutton View Post
I knew an old time Chevy racer state that the 3/8" rods were stronger than the 7/16" rods because there was more material in the weakest part of the rod than the bigger bolt ones where the bolt passed through.
I've heard the same thing several times from many racers. In addition, there are a lot of 454's with stock truck rods with stock bolts going thru the traps at 6500rpm's and higher and a lot do it for a few years. Some of 'em are connected to TRW Forged Bricks that weigh a ton! The biggest favor you can do for your rods and bolts is run lighter pistons.

I THINK that Chevy rods are 5140 steel but I'm not sure. I am sure they're not 4340.
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  #10  
Old Nov 20th, 09, 8:00 AM
68chvlss396 68chvlss396 is offline
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Default Re: BBC Connecting Rod Question

GM forged rods are 4340.

19170198
Forged Steel Connecting Rod


Magnafluxed 4340 steel with heavy-duty 7/16
" bolts
Machined for pressed piston pins and color-coded white
Used in Gen V 454 and 502 engines
6.135


" c-c length
Use rod bearing P/N 12329715

http://www.summitracing.com/parts/NA...2/?image=large

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  #11  
Old Nov 20th, 09, 9:29 AM
bcmiller bcmiller is offline
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Default Re: BBC Connecting Rod Question

Dave thanks for that information on the 4340 steel rods. Those are GEN V rods. Do you know if the rods used in the late 60s and through the 70s were the same composition?
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68 Camaro - 468 BBC, RPM Air-Gap intake, 781 heads, Lakewood bellhousing, M21, BO coded 12 bolt - but 3.31 Positraction now. Old drag car back on the street.
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  #12  
Old Nov 20th, 09, 10:05 AM
68chvlss396 68chvlss396 is offline
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Default Re: BBC Connecting Rod Question

Bryon, The LS6 and LS7 crate engines built on the MKIV blocks back in the 70's and 80's used the 7/16 dimple rod for pressed fit pins PN/3963552 and they were 4340 forged steel. I would imagine that all HP dimple rods regardless of 3/8's or 7/16's bolts are the same.
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  #13  
Old Nov 20th, 09, 10:13 AM
SILVERSS454 SILVERSS454 is offline
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Default Re: BBC Connecting Rod Question

I have a buddy who has run 9.90's for years in a bracket car, 468 with 3/8" truck rods and TRW pistons, shifting as high as 7200 rpm. Never had any kind of rotating assembly problems. He simply replaces the bearings every couple of years and that is it.
I have run 3/8" truck rods in every motor I have built. Always use ARP bolts. No problems whatsoever.
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  #14  
Old Nov 20th, 09, 11:22 AM
bcmiller bcmiller is offline
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Default Re: BBC Connecting Rod Question

Quote:
Originally Posted by 68chvlss396 View Post
Bryon, The LS6 and LS7 crate engines built on the MKIV blocks back in the 70's and 80's used the 7/16 dimple rod for pressed fit pins PN/3963552 and they were 4340 forged steel. I would imagine that all HP dimple rods regardless of 3/8's or 7/16's bolts are the same.
Thanks Dave. I really appreciate that information.
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Bolero Red 1967 Chevelle SS 396, bench seat 4 speed, 3.31 12 bolt posi - long term restoration project
68 Camaro - 468 BBC, RPM Air-Gap intake, 781 heads, Lakewood bellhousing, M21, BO coded 12 bolt - but 3.31 Positraction now. Old drag car back on the street.
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  #15  
Old Nov 20th, 09, 11:46 AM
Darracq Darracq is offline
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Default Re: BBC Connecting Rod Question

Quote:
Originally Posted by 68chvlss396 View Post
GM forged rods are 4340.

19170198
Forged Steel Connecting Rod


Magnafluxed 4340 steel with heavy-duty 7/16
" bolts
Machined for pressed piston pins and color-coded white
Used in Gen V 454 and 502 engines
6.135


" c-c length
Use rod bearing P/N 12329715

http://www.summitracing.com/parts/NA...2/?image=large



$118 a piece holly crap
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