Con Rod Offset?
#1660048
08/17/14 02:16 AM
08/17/14 02:16 AM
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Joined: Dec 2011
Posts: 257
Way North Idaho
1KoolBee
OP
enthusiast
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OP
enthusiast
Joined: Dec 2011
Posts: 257
Way North Idaho
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I'm contemplating building a "beater" 457 or 471 short-block for my '68 Bee so I can run it hard without fear of hurting the factory original 383. I had read some things about "connecting rod offset" of .060 towards crank cheek that is machined into BBC rods. Is that ideal for running BBC rods in a BB Mopar or would "centered" rods with BBC journals be better, or does it even matter?
'68 Bee 383/TF/Factory Air...high school sweetheart
'67 GTX Clone project,500 six pack,Hemi4-speed,Dana
05 Dodge Viper, 505 V-10, 6-speed Tremec
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Re: Con Rod Offset?
[Re: 1KoolBee]
#1660049
08/17/14 07:12 AM
08/17/14 07:12 AM
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Joined: Feb 2009
Posts: 1,532
off the grid
340B5
pro stock
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pro stock
Joined: Feb 2009
Posts: 1,532
off the grid
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You need the same offset as the Mopar rod, otherwise the rod will fatigue very quickly from being offset on the piston end.
Yeah, it's got a smallblock.
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Re: Con Rod Offset?
[Re: 340B5]
#1660050
08/17/14 10:32 PM
08/17/14 10:32 PM
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Joined: Dec 2011
Posts: 257
Way North Idaho
1KoolBee
OP
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OP
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Way North Idaho
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Quote:
You need the same offset as the Mopar rod, otherwise the rod will fatigue very quickly from being offset on the piston end.
So is a big Mopar offset .060 like a BBC ? Lots of Mopars run BBC rods with zero issues. Let me rephrase my question to get at what I'm trying to figure out: What is the proper offset (if any) for using a BBC style rod in big Mopar? Normal offset for BBC rod is .060 towards the crank counterweights. Normal for a BBC style rod for 460 ford is zero. ie the rod beam is directly centered over the big end. What should it be for Big Mopar?
Last edited by 1KoolBee; 08/18/14 03:45 AM.
'68 Bee 383/TF/Factory Air...high school sweetheart
'67 GTX Clone project,500 six pack,Hemi4-speed,Dana
05 Dodge Viper, 505 V-10, 6-speed Tremec
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Re: Con Rod Offset?
[Re: Cab_Burge]
#1660052
08/18/14 01:11 AM
08/18/14 01:11 AM
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Joined: Dec 2011
Posts: 257
Way North Idaho
1KoolBee
OP
enthusiast
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OP
enthusiast
Joined: Dec 2011
Posts: 257
Way North Idaho
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Quote:
Quote:
I'm contemplating building a "beater" 457 or 471 short-block for my '68 Bee so I can run it hard without fear of hurting the factory original 383. I had read some things about "connecting rod offset" of .060 towards crank cheek that is machined into BBC rods. Is that ideal for running BBC rods in a BB Mopar or would "centered" rods with BBC journals be better, or does it even matter?
Mopar uses a reverse fillet finish on thier crankshaft journals shoulders, GM uses a standard fillet so the BB Chevy end up being around .090 narrower on the rod widths than the standard BB mopar rod widths.  The offset your probally thinking of is in the crankshaft rod journals to increase the stroke, you grind the insides(towards the mains)of the Mopar rod journals down and out from 2.375 O.D. to 2.200 towards the outside of the rods journals to increase the stroke   If you decide to do this make sure and take the crank to a compentent shop that knows how to do that properly  Some other popular reduction in rod journal sizes are down to SB Chevy rod sizes, 2.100 and 2.00 as well as 1.88 Honda rod journal sizes  Be careful on any mods like that though
Hi Cab,
I'm aware of offset grinding a 3.75 stroke 440 crank to 3.915 with BBC sized journals. Actually I was planning to just buy a 440 source 3.915 crank with BBC journals & sell the steel 440 crank I have since its only about $300 more to buy new when you figure in the cost of machining the 440 crank and counterweights for a low deck. What I'm talking about is the big end axis of bbc rod is apparently offset machined about .060 off the axis of the beam and the pin end. BTW still planning to move your way in a few years, just taken a detour to the San Diego area for now..
'68 Bee 383/TF/Factory Air...high school sweetheart
'67 GTX Clone project,500 six pack,Hemi4-speed,Dana
05 Dodge Viper, 505 V-10, 6-speed Tremec
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Re: Con Rod Offset?
[Re: 1KoolBee]
#1660053
08/18/14 01:30 AM
08/18/14 01:30 AM
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Joined: Jan 2003
Posts: 6,591
Canton, Ohio
Sport440
master
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master
Joined: Jan 2003
Posts: 6,591
Canton, Ohio
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Quote:
I'm contemplating building a "beater" 457 or 471 short-block for my '68 Bee so I can run it hard without fear of hurting the factory original 383. I had read some things about "connecting rod offset" of .060 towards crank cheek that is machined into BBC rods. Is that ideal for running BBC rods in a BB Mopar or would "centered" rods with BBC journals be better, or does it even matter?
Dont know about the .060 offset built into the chevy rods.
On the Mopars, the offset was built into the Pistons.
As far as I know All aftermarket stuff is centered. Both pistons and rods. You have no choice, unless you pay for custom.
On stock mopar stuff there was a benefit by reversing/flopping the Pistons offset for more power.
And for a race/street engine, No , It doesnt really matter. The Factory offset was to make the engine run smoother.
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Re: Con Rod Offset?
[Re: Sport440]
#1660054
08/18/14 02:06 PM
08/18/14 02:06 PM
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Joined: Jan 2003
Posts: 16,376
dogdays
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 16,376
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The offset built into the pistons is the offset PIN. This is sideways as you're looking at the engine from a crankshaft end. This is offset to reduce piston slap. It's usually 0.060. Aftermarket wristpins are at zero offset, usually. Back in the day, Mopar racers found a few horsepower by turning the pistons around to reverse this offset. There is still discussion why it works.
There's a new engine family, I believe it is by Jaguar, that uses an offset crank. Again, this is side-to-side. And there's a new piston design that moves the pin to reduce thrust loading, I think it's a Mahle.
The original poster was, IMHO, referring to the offset of the rod big end cheeks to the centerline of the rod shank. This has nothing to do with piston pin offset. I have been having some of the same questions. In terms of looking at the engine from a crank end, this offset moves the connecting rod toward or away from you. At least one reply is talking about this, but many seem to be fixated on wristpin offset.
R.
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Re: Con Rod Offset?
[Re: 1KoolBee]
#1660055
08/18/14 09:37 PM
08/18/14 09:37 PM
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Joined: Aug 2003
Posts: 1,313
Charlotte, NC
LSP
pro stock
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pro stock
Joined: Aug 2003
Posts: 1,313
Charlotte, NC
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Quote:
I'm contemplating building a "beater" 457 or 471 short-block for my '68 Bee so I can run it hard without fear of hurting the factory original 383. I had read some things about "connecting rod offset" of .060 towards crank cheek that is machined into BBC rods. Is that ideal for running BBC rods in a BB Mopar or would "centered" rods with BBC journals be better, or does it even matter?
It matters if your racing in a competitive class, but not for your beater, just put it together with BBC or BBM rods as is.
Ford and some LS rods are centered, offset and centered rods are not interchangeable without some calculating, and sometimes, machine work.
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Re: Con Rod Offset?
[Re: LSP]
#1660056
08/18/14 11:40 PM
08/18/14 11:40 PM
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Joined: Dec 2011
Posts: 257
Way North Idaho
1KoolBee
OP
enthusiast
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OP
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Joined: Dec 2011
Posts: 257
Way North Idaho
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Quote:
Quote:
I'm contemplating building a "beater" 457 or 471 short-block for my '68 Bee so I can run it hard without fear of hurting the factory original 383. I had read some things about "connecting rod offset" of .060 towards crank cheek that is machined into BBC rods. Is that ideal for running BBC rods in a BB Mopar or would "centered" rods with BBC journals be better, or does it even matter?
It matters if your racing in a competitive class, but not for your beater, just put it together with BBC or BBM rods as is.
Ford and some LS rods are centered, offset and centered rods are not interchangeable without some calculating, and sometimes, machine work.
Thanks LSP and dogdays, you've got it. From what I've read, its not a big deal within reason, but what I don't know is what the "normal" offset is for a big Mopar. For example, if mopar "normal" is zero, then a zero offset BBC rod would be off-center by about .015 in a mopar BB engine while an .060 offset BBC rod would be off-center by .045 (.060 - BBC crank journal width difference/2) in the opposite direction.
On the other hand, if BB mopar rods are offset .045, a BBC rod with .060 offset would be perfect.
Confused yet!?
I have a choice at this stage of the game, less is better, just not sure which is best. Thanks everyone for your help.
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