3.4 rods to 3.8

[97 30th RS]

A buddy of mine asked if he could use rods from a 3.4 liter and put him in his 3.8 because he thinks that shorter rods will let themotor spin higher, due to less rotating mass. What the heck shouldI tell him?

[fenderman]

Well, the crank is not going to compensate for the shorter throw, so the pistons will not travel as far up the combustion chamber, thus lowering the compression and making the motor run like crap. I don't know either how far the piston travels downwards with the stock rods, but if the rods from the 3.4 are that much shorter, you may do some damage on the down stroke with a ring or something if it got past that point. While I am not sure on this last point, I do know for sure that if the piston does not travel as far, you'll destroy the compression and actually lose power in the motor.