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Author Topic:   Will this balance easy? (Bobweight question)
posted November 28, 2004 08:16 PM
OK - I've totally blanked out on the bobweight calculation - and am looking to order some parts - the crank I'm considering has a bobweight of 1750,1830 or 1900 avaialable - the 6" rods are H-beam LW that weight about 550gr or I can get the 'heavier' ones that weigh around 600gr. The pistons weigh approx 440gram (JE's web site for their SRP flat-tops)

Anyhow - which combo would balance easiest??

OR - how do I know what crank or rods will be the best to go with to balance easier with minimal heavy metal Or if someone can post the formula that would be great!

posted November 28, 2004 09:20 PM
I personally would go with the 1830 crank. try taking out 70 grams....that's a ton of work. I didn't go to the JE website, but I assume the 440 gram pistons still need pins.... and what ring pack would you run?

Most racing motors are under 1800 bob weight, I built one last year that was 1745 grams......that was stock rods, JE flat top pistons (short pin, thin wall), along with thin metric rings.......

bob weight is .....2 times pistons, pins, rings, and small end of the 1 of the bid ends of the rod and bearing...

2 of the recip. parts PLUS 1 of the rotating parts...... or at least thats what I remember..... I'm sure someone will correct my quickly if i'm mistaken, they always do........

posted November 29, 2004 07:35 AM
Originally posted by autoshop:
if it was me and i had a choice I would go with the light bobweight, It's a lot simpler to drill holes to balance. with the 1900 your looking to add weight to the crank somewhere.

Wouldn't that be opposite - removing material from the crank that's a heavier bobweight and adding it to the lighter??