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Balance...neutral.....over.....under..????

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Balance...neutral.....over.....under..????

Postby Ron Clevenger » Tue Jan 29, 2013 11:06 am

Question to those that are knowledgeable about the affects of balancing.

I run a high dollar blower crank, is it better to balance straight up or 52% over or under???

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Re: Balance...neutral.....over.....under..????

Postby CNC BLOCKS » Tue Jan 29, 2013 11:45 am

Ron Clevenger wrote:Question to those that are knowledgeable about the affects of balancing.

I run a high dollar blower crank, is it better to balance straight up or 52% over or under???

Blessings...........Ron


Straight up or over if anything never under.

If its a lot of RPM Over does not hurt.
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Re: Balance...neutral.....over.....under..????

Postby ap72 » Tue Jan 29, 2013 12:06 pm

So if its low RPM would under be more appropriate?
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Re: Balance...neutral.....over.....under..????

Postby CNC BLOCKS » Tue Jan 29, 2013 12:27 pm

ap72 wrote:So if its low RPM would under be more appropriate?


Never under balance anything !!
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Re: Balance...neutral.....over.....under..????

Postby Ron Clevenger » Tue Jan 29, 2013 1:07 pm

Balancing is an area I've just never took the time to study. I've always balanced neutral. But this last time it was balanced 52% over. Motors a 565 big chief BBC with 40 psi of boost going through it with very good parts. Race "outlaw racing" and with my budget the top rpm is 8600-8700.

I'm sure I won't notice anything different from neutral to 52% over in the performance. But was just wondering what the physical effects would be on the motor. This year we are racing "Outlaw Eliminator" which runs on a 6.20 1/4 mile index. So the motor will be utilizing more of it's power potential.

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Re: Balance...neutral.....over.....under..????

Postby SchmidtMotorWorks » Tue Jan 29, 2013 3:25 pm

What is the purpose of over balance?
If 2% is good, why wouldn't 4% be better and why wouldn't 10% be still better yet?
How is under-balance different than over-balance? Why is one better than the other?

If I remove CW #2 from a crank and get it to balance by adding metal to CW #1, is it properly balanced? If I add more weight to #1 to over balance it, it that an improvement?

The answer is, over/underbalance tells you close to nothing about the CW design in a crank.
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Re: Balance...neutral.....over.....under..????

Postby af2 » Tue Jan 29, 2013 4:10 pm

SchmidtMotorWorks wrote:What is the purpose of over balance?
If 2% is good, why wouldn't 4% be better and why wouldn't 10% be still better yet?
How is under-balance different than over-balance? Why is one better than the other?

If I remove CW #2 from a crank and get it to balance by adding metal to CW #1, is it properly balanced? If I add more weight to #1 to over balance it, it that an improvement?

The answer is, over/underbalance tells you close to nothing about the CW design in a crank.


Still listening. This has been interesting with a 9500 rpm blown car also that needs rods replaced at 25 runs.
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Re: Balance...neutral.....over.....under..????

Postby CNC BLOCKS » Tue Jan 29, 2013 4:18 pm

af2 wrote:
SchmidtMotorWorks wrote:What is the purpose of over balance?
If 2% is good, why wouldn't 4% be better and why wouldn't 10% be still better yet?
How is under-balance different than over-balance? Why is one better than the other?

If I remove CW #2 from a crank and get it to balance by adding metal to CW #1, is it properly balanced? If I add more weight to #1 to over balance it, it that an improvement?

The answer is, over/underbalance tells you close to nothing about the CW design in a crank.


Still listening. This has been interesting with a 9500 rpm blown car also that needs rods replaced at 25 runs.



I have bought crank shafts for King's crankshaft for years and Have talked to rick about over balance and he has balanced for some cup teams over the years and has done up to a 4% over balance on some those cranks.

I have build 2 blower engines and are chipped at 9500 one is 2% over balanced the is straight up and the beaings on both look great after 50 plus hooks and they could run up to 30 seconds a hook, Pulling tractors.

Do search on over and under balnce you should find what your looking for.
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Re: Balance...neutral.....over.....under..????

Postby SchmidtMotorWorks » Tue Jan 29, 2013 4:30 pm

I have bought crank shafts for King's crankshaft for years and Have talked to rick about over balance and he has balanced for some cup teams over the years and has done up to a 4% over balance on some those cranks.

I have build 2 blower engines and are chipped at 9500 one is 2% over balanced the is straight up and the beaings on both look great after 50 plus hooks and they could run up to 30 seconds a hook, Pulling tractors.

Do search on over and under balnce you should find what your looking for.http://WWW.CNCBLOCKSNE.COM
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I'll buy lunch for anyone that can post a physics based reason to use overbalance besides compensation for filling the oil holes.

I have made and balanced 100's of billet cranks for many forms of racing and have yet to hear an explanation for why anyone would use overbalance other than "that is what I heard someone else did".

Fewer people do it now than they used to.

Flat cranks typically have CWs way under balanced, the main reason 90 degree cranks don't use underbalance is the vibration.

The standard practice of overbalancing is easily debunked by the fact that you can over balance a crank by adding to the end CW or 2nd or 3rd (in from the ends) and get the same result.
Obviously, adding that weight to the different CWs has a different effect on the loads within the crank.
The problem is a crankshaft balancing machine is not capable of measuring the loads within the crank.
Last edited by SchmidtMotorWorks on Tue Jan 29, 2013 4:34 pm, edited 2 times in total.
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Re: Balance...neutral.....over.....under..????

Postby SchmidtMotorWorks » Tue Jan 29, 2013 4:32 pm

af2 wrote:
SchmidtMotorWorks wrote:What is the purpose of over balance?
If 2% is good, why wouldn't 4% be better and why wouldn't 10% be still better yet?
How is under-balance different than over-balance? Why is one better than the other?

If I remove CW #2 from a crank and get it to balance by adding metal to CW #1, is it properly balanced? If I add more weight to #1 to over balance it, it that an improvement?

The answer is, over/underbalance tells you close to nothing about the CW design in a crank.


Still listening. This has been interesting with a 9500 rpm blown car also that needs rods replaced at 25 runs.



Are you thinking crank balance has something to do with the rod problem? If so, why?
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Re: Balance...neutral.....over.....under..????

Postby DaveMcLain » Tue Jan 29, 2013 4:35 pm

I always thought that the only reason it possibly could make any difference is because the motion of the pistons in the engine is not sinusoidal and they approach and leave BDC at a slightly different rate than at TDC and adding a little extra mass to the counterweight helps to cancel out the forces generated by the differences.

With that said I've never used "overbalancing" except for allowing about 3 grams for oil and I've had drag race guys with blower engines turn over 10,000 rpm with no balance related problems. I'm not convinced that it's a big deal either...
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Re: Balance...neutral.....over.....under..????

Postby SchmidtMotorWorks » Tue Jan 29, 2013 4:40 pm

DaveMcLain wrote:I always thought that the only reason it possibly could make any difference is because the motion of the pistons in the engine is not sinusoidal and they approach and leave BDC at a slightly different rate than at TDC and adding a little extra mass to the counterweight helps to cancel out the forces generated by the differences.

With that said I've never used "overbalancing" except for allowing about 3 grams for oil and I've had drag race guys with blower engines turn over 10,000 rpm with no balance related problems. I'm not convinced that it's a big deal either...



Yep, Allan Lockheed years ago made a software called Engine Expert that graphed the difference in loads from that, problem is over balance would be present at both TDC and BDC.

Engine Expert is an interesting software to look at, you can still get it at:

http://www.audietech.com/engine-expert/ ... xpert.html
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Re: Balance...neutral.....over.....under..????

Postby zums » Tue Jan 29, 2013 8:43 pm

in 1996 i picked up my crank after paying for it to be balanced at jenkins, it was overbalanced 52% ,, i didnt argue with him, many 9700-9800 rpm shifts later, i still wouldnt argue with him
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Re: Balance...neutral.....over.....under..????

Postby MadBill » Tue Jan 29, 2013 8:56 pm

Balance theory assumes a rigid crank. I started to ponder the effects of the slight but inevitable centrifugally-induced distortion at high RPM, but it would seem a 'rubber crank' would fling its CWs outwards, thus mimicking a higher balance percentage, so no explanation there..
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Re: Balance...neutral.....over.....under..????

Postby af2 » Tue Jan 29, 2013 9:04 pm

SchmidtMotorWorks wrote:
af2 wrote:
SchmidtMotorWorks wrote:What is the purpose of over balance?
If 2% is good, why wouldn't 4% be better and why wouldn't 10% be still better yet?
How is under-balance different than over-balance? Why is one better than the other?

If I remove CW #2 from a crank and get it to balance by adding metal to CW #1, is it properly balanced? If I add more weight to #1 to over balance it, it that an improvement?

The answer is, over/underbalance tells you close to nothing about the CW design in a crank.


Still listening. This has been interesting with a 9500 rpm blown car also that needs rods replaced at 25 runs.



Are you thinking crank balance has something to do with the rod problem? If so, why?


Not at all... I was wondering like usual. Maybe something else could be improved on. That is all.
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