I'm gearing up for a budget rebuild. I have the following parts and planning on getting the rest.

Already Have
1-piece block
stock crank in good shape, just needs polished and magnafluxed
PM rods

Need
Pistons
rings
bearings
heads


My question is when do you really need to have the rotating assymbly balanced. I've never done it with past rebuilds using stock stuff with flat top pistons. The motor never felt ruff, or wore bearings funny. I'm worried because I've heard it mentioned that the PM rods were lighter than stock. Is this true? If so do you think a balance job is going to be absolutely necesary? I have a friend who slapped a motor together with lunatic pro-mod rods and forged pistons and it shook so bad he pulled the motor down to get it balanced, I expected it with a setup that far from stock. This rebuild has to be done on the cheap, but I'm not going to cut corners that will come back to bite me in 50,000 miles. I'm just looking for a motor that will make 300 to the wheels reliably.

 

PM rods are lighter than the other types of factory rods. Balancing may not be absolutely necessary, but will add to engien longevity. The common axiom is that with a stock crank and PM rods, it is better to use a 305 crank than a 350 crank siince it is balanced more closely to the lighter piston/rod assemblies.

 

If they are light enough to require using a 305 crank, I'm going to go ahead and get the whole assymbly balanced. Just kinda sucks to have more in the balance job than the whole rotating assymbly.

This motor is destined for lots of road course abuse. I'm aiming for 300-330 at the wheels and it won't be reved over 6k. Just needs to be able take 4-6K for 20 minutes at a time. I'm spending alot of time making sure the oiling system is up to the task.

Vader: I've read that the PM rods could have came from the factory with or without the cracked cap. I don't have my rods yet, so I'm not sure what I have. Do you know if you can swap out the stock rod bolts for ARP's without resizing since they have the cracked caps for alignment? GM rates these things to 450 HP so I'm not too worried about them, just want the added fatigue resistance of the ARP bolts.