balancing
First I've heard of "over-balancing"....usually a machine shop wants to know what you're going to spin it to and then balance it accordingly. I guess you could tell them 8K RPM and only spin to 7K, but that would be fairly safe IMO....
i run a 49/51% over balance on my motor...........works out fantastic for stroked motors planning on spending most of their time above 5000rpm+.........that little extra weight really helps to pull the rod/piston back down the bore espically at very high rpm.....
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The "over-balancing" I have heard about has nothing to do with what RPM you're spinning the motor to.
Over balancing is just adding an additional 1/2% to 1% to the "exact" calculated bobweight, and then balancing the rotating assembly for that "new" bobweight.
For example, say all the rotating assembly componets you're going to use in an engine build, require an "exact" 1,500 gram "calculated" bobweight. To "over balance" this rotating assembly by 1%, you would add, 1% times 1,500 grams = 15 (additional) grams, for a total of a 1,515 gram bobweight, and then "balance" the assembly using this new "over-balanced" 1,515 gram bobweight.
Using a 1,515 gram bobweight, instead of the "exactly" called for 1,500 gram bobweight, (in this example) ........ would give you an engine "over-balanced" by 1%. Got it???
And, just for the OP, yes most all NASCAR engines are "over-balanced" by between 1/2% to 1%.
Did you mean to say you've NEVER heard of "over-balancing" in the above quote???
The "over-balancing" I have heard about has nothing to do with what RPM you're spinning the motor to.
Over balancing is just adding an additional 1/2% to 1% to the "exact" calculated bobweight, and then balancing the rotating assembly for that "new" bobweight.
For example, say all the rotating assembly componets you're going to use in an engine build, require an "exact" 1,500 gram "calculated" bobweight. To "over balance" this rotating assembly by 1%, you would add, 1% times 1,500 grams = 15 (additional) grams, for a total of a 1,515 gram bobweight, and then "balance" the assembly using this new "over-balanced" 1,515 gram bobweight.
Using a 1,515 gram bobweight, instead of the "exactly" called for 1,500 gram bobweight, (in this example) ........ would give you an engine "over-balanced" by 1%. Got it???
And, just for the OP, yes most all NASCAR engines are "over-balanced" by between 1/2% to 1%.
The "over-balancing" I have heard about has nothing to do with what RPM you're spinning the motor to.
Over balancing is just adding an additional 1/2% to 1% to the "exact" calculated bobweight, and then balancing the rotating assembly for that "new" bobweight.
For example, say all the rotating assembly componets you're going to use in an engine build, require an "exact" 1,500 gram "calculated" bobweight. To "over balance" this rotating assembly by 1%, you would add, 1% times 1,500 grams = 15 (additional) grams, for a total of a 1,515 gram bobweight, and then "balance" the assembly using this new "over-balanced" 1,515 gram bobweight.
Using a 1,515 gram bobweight, instead of the "exactly" called for 1,500 gram bobweight, (in this example) ........ would give you an engine "over-balanced" by 1%. Got it???
And, just for the OP, yes most all NASCAR engines are "over-balanced" by between 1/2% to 1%.
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You know what, you learn something new everyday... That being said I can see the benefit on a race engine, but to me, it seems it would add extra wear and tear on a DD street engine. But then again, I don't look for RPM over 6500 for a street engine. Not in an SBC anyway. But again this is just me...
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My comment regarding "having nothing to do with RPM" was aimed at poster duh, who seemed to imply to the OP that an engine builder will balance an engine differently if you tell them to balance it for 7,000 RPM vs 8,000 RPM; and that is definitely ...... WRONG!
The "usage" example I cited, namely NASCAR engines ........ "pionerred" the concept of "over-balancing" engines for high RPM racing, because, unlike in drag racing ........... their motors run for hours at 9,000+ RPM versus just seconds ...... like they do in 1/4 mile racing.
In truth, ANY engine can benefit from "over-balancing", it will just be MORE beneficial at higher RPM.
Hope this clears things up.
Last edited by 97 6speed z; Jul 18, 2011 at 03:00 PM. Reason: Spelling
But again this seems it would add unnecessary wear on the bearings due to more force being applied to them. Granted that could be accounted for by loosening up the bearing tolerances a bit to allow more of an oil cushion...
(d*mn engine theory)
At least we agree on the "High RPM" part now!
My comment regarding "having nothing to do with RPM" was aimed at poster duh, who seemed to imply to the OP that an engine builder will balance an engine differently if you tell them to balance it for 7,000 RPM vs 8,000 RPM; and that is definitely ...... WRONG!
The "usage" example I cited, namely NASCAR engines ........ "pionerred" the concept of "over-balancing" engines for high RPM racing, because, unlike in drag racing ........... their motors run for hours at 9,000+ RPM versus just seconds ...... like they do in 1/4 mile racing.
In truth, ANY engine can benefit from "over-balancing", it will just be MORE beneficial at higher RPM.
Hope this clears things up.
My comment regarding "having nothing to do with RPM" was aimed at poster duh, who seemed to imply to the OP that an engine builder will balance an engine differently if you tell them to balance it for 7,000 RPM vs 8,000 RPM; and that is definitely ...... WRONG!
The "usage" example I cited, namely NASCAR engines ........ "pionerred" the concept of "over-balancing" engines for high RPM racing, because, unlike in drag racing ........... their motors run for hours at 9,000+ RPM versus just seconds ...... like they do in 1/4 mile racing.
In truth, ANY engine can benefit from "over-balancing", it will just be MORE beneficial at higher RPM.
Hope this clears things up.
HaHa you guys are funny!!! I know exactly what over-balancing is... I was just wondering if there a few that have done it to their exact setup. No need for a theory discussion!!
yea i know u know lol........like i said i have a 49/51 on the current 385 in my car now.....
