hope some one has the answer to this one. I need to assemble my bottom end on my L98. the 350 crank i was going to use is junk(grooved) I do however have a brand new 305 crank (both are one piece style). I know that the counter wieghts for the cranks a diffrent however i weighed a 305 pistion/rod and my 350 pistion/rod are very close in wieght about (4grams) this is because I have light weight 350 pistons and rods just happened to work out. my reasoning says this will work. what do you guys think?

 

The lightweight 350 pistons are 4 grams heavier than the 305s?

 

here what i came up with OE pistion and rod 2lbs 15.30oz= 1398 grams
my new ones 2lbs 12.90oz = 1328grams
305 oe piston/rods 2lbs 12.60oz= 1319 grams ( i was off its 9grams)

the old from the new does not sound like alot but thats about 3oz per unit times 8 =16 oz or 1pound and that is rotating mass. i feel like i am close enough to use the 305 crank but i want to see what you guys think.

 

Pistons are reciprocating mass, not rotating mass. 9 grams is still a whole lot of weight difference. You might be able to add enough steel to the crank to make up the difference in balance without having to use the expensive stuff, the machine shop that does your balancing will be able to tell you.