I have a set of 6 Lunati Pro Mod big block rods that I managed to find a pair of near-identical replacements for. The only difference is that the originals are a bit heavier than the spares - about 24 grams total. In an engine that won't see the high side of 6K, is it possible to use a different bob weight on one rod pin and balance accordingly? I'm figuring that if they go on either the front or back pin it would possibly work better since it wouldn't affect adjacent rods on each side. I'm trying to avoid replacing those two with identical weight rods as they're about $100 apiece. Thanks for your help!
What has been changed in the rod design to add 24 grams? Is it all on one end or is the whole rod been redesigned?
24 grams in the same style & brand of rod is quite a bit.
It does not sound like the best plan to me.
Will it work? I honestly don't know but I would not want to be responsible for it.
There is a deal called "couple" which is the interaction of one end to the other or the center to both ends of a shaft (crank in this case)
What you do to one end effects the other to a certain extent.
You can take a shaft, add two flywheels with equal & opposing weights, one on each end & statically it will be in balance but dynamically it will go nuts.
This is the reason that internally balanced performance engines especially in endurance applications seem to be easier on main bearings.
The best way to balance an engine is to locate the counterweights equally along the shaft but this is sometimes not possible so you add or subtract weight where you can.
The longer the stroke the more problems you encounter & this is part of the reason you find added counterweight at the center of longer stroker cranks.