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  Fully counterweighted crankshaft versus not being fully counterweighted.

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Author Topic:   Fully counterweighted crankshaft versus not being fully counterweighted.
ted
Journeyman

Posts: 75
From: Central Texas
Registered: May 2003

posted 05-11-2003 04:18 PM     Click Here to See the Profile for ted   Click Here to Email ted     Edit/Delete Message   Reply w/Quote
Everything else being equal and both crankshafts being internally balanced, are there any inherit advantages of the fully counterweighted crankshafts and those that aren't. What are the pros and cons of each design? I'm in the process or ordering another billet crank and I'm getting conflicting information from the various crankshaft builders concerning this area.

I've run both styles in the past without any bearing or wear issues which means balanced is balanced. On the other hand, are there any strees or rpm limitations with one design over the other?

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Ted E.
Fe's are plenty fast, but "Y"'s are fun when they run in the nines.

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Moneymaker
Administrator

Posts: 26813
From: Lyons, IL, USA
Registered: May 99

posted 05-11-2003 04:59 PM     Click Here to See the Profile for Moneymaker   Click Here to Email Moneymaker     Edit/Delete Message   Reply w/Quote
Welcome to M&M Ted.
The answer is rather obvious (to me anyway).
Lighter is ALWAYS quicker and as smaller is lighter, I would opt of the lighter of the two.
I have never seen any benefit or gain using a fully counter weighted crank.

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Alex Denysenko
Co-Administrator and Moderator

NHRA/IHRA/SRA member and licensed Superstock driver
MCA member# 53321
NHRA and IHRA SS/LA National Record Holder '00,'01,'02,&'03
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bifs66
Gearhead

Posts: 272
From: Maryland
Registered: Apr 2000

posted 05-11-2003 05:41 PM     Click Here to See the Profile for bifs66   Click Here to Email bifs66     Edit/Delete Message   Reply w/Quote
There may be some academic theory that a fully balanced crank is "better for racing" than the externally balanced ones we see in the SBFs; but I don't know what that may be. From what I have read regarding the initial design and development of the SBFs (221/260/289), external balancing was decided upon in order to create a light, compact cast iron engine that could rival existing aluminum blocks of similar displacement. By putting the "supplemental counter weights" on the ends of the crank, they were able to make the crank/engine light and compact which allowed the block crankcase to be compact too. IIRC, it had something to do with balancing the rotating assembly using lighter weight than otherwise would be necessary. As I recall, the 289 was about 100 lbs lighter than the SBC; and as Alex said, weight (static and rotating) is a big factor. Maybe that's why SBFs and its newer cousin 5.0s always sound more eager to rev than other V-8 engines.

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Bernie Frank
66 Fastback restomod project
85 GT (preserved)
2000 SVT CONTOUR

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Rustang
Gearhead

Posts: 805
From: Clarion PA
Registered: Nov 2000

posted 05-12-2003 07:55 AM     Click Here to See the Profile for Rustang   Click Here to Email Rustang     Edit/Delete Message   Reply w/Quote
Having recently broken a 28oz external balance crank, I become enlightened on this deal.
First off, there's got to be a reason you see no external balanced engines in nascar, pro-stock, etc.. Even going back to Clevelands run in the 70's in nascar and pro stock they went to alot of problems to internal balance.
I spun my 28oz Windsor motor to 7200RPM at the track and on the street. It stayed together since 1989 and it's still together today. When it came time to build my "clevor" motor, I figured what's a few hundred more RPM? So I went the cheap route and stayed at the 28oz.. 20 8000rpm passes later, the crank breaks. I call the the guy that did my bottom end work (A very respected guy in the Pittsburgh area) and here was his explanation (after saying "I told you to internal balance!!"): First off, he asked if it broke at the first rod journal, which it did. He then proceeded to tell me that's a common failure in an external balance Ford engine at the r's I was running. The crank actually starts to torsionally bend due to the affect of the counterweights, and flexing was something a cast iron crank just won't do!
Just my .02

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'68 mustang 351 clevor- [email protected]
'67 Stang, 351W [email protected]
'69 351C [email protected]
'78 Pickup [email protected]
'79 Pickup 460 ET=??

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Moneymaker
Administrator

Posts: 26813
From: Lyons, IL, USA
Registered: May 99

posted 05-12-2003 09:58 AM     Click Here to See the Profile for Moneymaker   Click Here to Email Moneymaker     Edit/Delete Message   Reply w/Quote
The question was regarding fully counter weighted cranks vs non.
Not internal vs external balance.
Internal balance is ALWAYS the best way to go.

------------------
Alex Denysenko
Co-Administrator and Moderator

NHRA/IHRA/SRA member and licensed Superstock driver
MCA member# 53321
NHRA and IHRA SS/LA National Record Holder '00,'01,'02,&'03
First SS/MA in the TENS!
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28
Professional Manwhore
The Barry of BarrysGrrl

Quote #1: "I never met a magazine mechanic I liked."
Quote #2: "Make sure brain is in gear before engaging mouth!"
Quote #3: "If you can't run with the big dogs, stay on the porch!"
www.moneymakerracing.com

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Rustang
Gearhead

Posts: 805
From: Clarion PA
Registered: Nov 2000

posted 05-12-2003 12:50 PM     Click Here to See the Profile for Rustang   Click Here to Email Rustang     Edit/Delete Message   Reply w/Quote
uh.. .um..oh yeah...I was just seein' if you were paying attention

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Moneymaker
Administrator

Posts: 26813
From: Lyons, IL, USA
Registered: May 99

posted 05-12-2003 01:07 PM     Click Here to See the Profile for Moneymaker   Click Here to Email Moneymaker     Edit/Delete Message   Reply w/Quote
LOL

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Alex Denysenko
Co-Administrator and Moderator

NHRA/IHRA/SRA member and licensed Superstock driver
MCA member# 53321
NHRA and IHRA SS/LA National Record Holder '00,'01,'02,&'03
First SS/MA in the TENS!
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28
Professional Manwhore
The Barry of BarrysGrrl

Quote #1: "I never met a magazine mechanic I liked."
Quote #2: "Make sure brain is in gear before engaging mouth!"
Quote #3: "If you can't run with the big dogs, stay on the porch!"
www.moneymakerracing.com

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