To balance or not balance??
05-12-2014, 10:31 AM
#1
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To balance or not balance?? So here is my question. Should I have the rotating assembly balanced or not. I've read so much about the subject that now I'm confused. Some say if it's less than 50 grams total difference it doesn't matter. ?? Plus other factors are flywheel / flexplate, etc...
My car was originally a M6. Which means it had a heavy *** flywheel. Now that it's an A4 it has a much lighter flexplate. Which it didn't get balanced after that change.
Also, I'm keeping the stock crank and rods. The only thing changing internally is the pistons and pins. Still stock bore pistons. I'm changing the stock pistons for the Mahle Forged pistons.
So my question is this. Is it worth the money for the balance? From what I've found there is only 6 grams difference between the piston weights with the new ones being lighter than stock.
It may be a stupid question but I have to ask.
My car was originally a M6. Which means it had a heavy *** flywheel. Now that it's an A4 it has a much lighter flexplate. Which it didn't get balanced after that change.
Also, I'm keeping the stock crank and rods. The only thing changing internally is the pistons and pins. Still stock bore pistons. I'm changing the stock pistons for the Mahle Forged pistons.
So my question is this. Is it worth the money for the balance? From what I've found there is only 6 grams difference between the piston weights with the new ones being lighter than stock.
It may be a stupid question but I have to ask.
05-12-2014, 12:05 PM
#6
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I'd say it depends on your budget and intended use. A sheet of paper weighs 4.5 grams just to give you and idea of how little 6 grams is. But you also have to consider that the stock balance probably isn't that good to start with so having it balanced could still have some benefit even with stock pistons.
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05-12-2014, 02:20 PM
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It'll be on it's way to get balanced tomorrow. Hell, $200 for a good balance is way cheaper than anything else I've done building this motor. This car does get beat on. It's not a garage queen and I don't really take it on cruises around town.
05-13-2014, 05:54 AM
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I've always wondered about that. Is it a HP gain? I've heard that for years.
I looked up 48 grams which is what the total difference in pistons and pins would be. 48 g = 1.69 ozs lighter than stock pistons. That , spread over the entire engine, doesn't seem like much but at high rpm's I guess it is. I talked with the machine shop yesterday and they said it would be balanced to within 1/2 a gram.
I looked up 48 grams which is what the total difference in pistons and pins would be. 48 g = 1.69 ozs lighter than stock pistons. That , spread over the entire engine, doesn't seem like much but at high rpm's I guess it is. I talked with the machine shop yesterday and they said it would be balanced to within 1/2 a gram.
05-13-2014, 08:22 PM
#12
^^^Let's say that the previous version of your engine was balanced. This would be based on all of the differences in weight, distributed throughout the assembly.
Then, along comes 48 grams less, distributed in a different manner than the above. A rebalance would be imperative.
Conversely to paragraph one, let's say that the previous version was not balanced. Still, reducing your assy by 48 grams would still require a rebalance.
Then, along comes 48 grams less, distributed in a different manner than the above. A rebalance would be imperative.
Conversely to paragraph one, let's say that the previous version was not balanced. Still, reducing your assy by 48 grams would still require a rebalance.
05-13-2014, 09:28 PM
#13
TECH Addict
A 3.66" stroke generates 2195 G forces at 6500rpms. That's not a typo.
6 grams static unbalanced = 29.39lbs of unbalanced rotating weight.
50 grams static unbalanced is 244.97lbs of unbalanced rotating force. That is significant.
What needs to be specified is 50g unbalanced at what rpms. If it's 50g at 6000rpms you are golden. If it's static it is really bad.
If it's 50g at 1000rpms, that is about 50 G's at 1000rpms with a 3.66" Stroke, comes out to 1gram static unbalanced weight. Or 4.9lbs at 6500 rpms.
For those that care, the equation for rotational g-forces is:
RCF = 1.118 * (10^-5) * r * (rpm)^2
Where:
RCF = Rotational Centrifugal Force (G-forces)
r = radius in cm
(rpm)^2 = revolutions per minute X revolutions per minute
16 oz per pound
28.3495 grams per ounce
Or 453.592 ( I round up to an easy to remember 454 grams per pound)
I had mine balanced to 9.5 grams at 1500rpms (or about 0.09grams static and about 0.412lbs at 6500rpms).
6 grams static unbalanced = 29.39lbs of unbalanced rotating weight.
50 grams static unbalanced is 244.97lbs of unbalanced rotating force. That is significant.
What needs to be specified is 50g unbalanced at what rpms. If it's 50g at 6000rpms you are golden. If it's static it is really bad.
If it's 50g at 1000rpms, that is about 50 G's at 1000rpms with a 3.66" Stroke, comes out to 1gram static unbalanced weight. Or 4.9lbs at 6500 rpms.
For those that care, the equation for rotational g-forces is:
RCF = 1.118 * (10^-5) * r * (rpm)^2
Where:
RCF = Rotational Centrifugal Force (G-forces)
r = radius in cm
(rpm)^2 = revolutions per minute X revolutions per minute
16 oz per pound
28.3495 grams per ounce
Or 453.592 ( I round up to an easy to remember 454 grams per pound)
I had mine balanced to 9.5 grams at 1500rpms (or about 0.09grams static and about 0.412lbs at 6500rpms).
Last edited by hrcslam; 05-14-2014 at 05:59 AM.