Hey everyone I am thinking about doning a low buck 383 rebuild using a Scat 9000 crank & 5.7" 4340 I rods with Speed Pro coated forged pistons & rings. My question is about the harmonic balancer/lower pulley, is it ok to use the factory one or do I have to buy one of the expensive ATI or Fluidamper?
I'm wondering if the added stroke will cause any problems even if the crank is balanced like the stocker?
This engine will have ported LT1 heads, intake and a 230/230 - .560/.560 cam and is a daily driver which will only be raced occasionally.
One other question if rpms are kept below 6500 is a 4 bolt main conversion necessary or can I get by with main studs and/or a main girdle?
Thanks in advance for any and all help you guys/girls can give.

 

IMO, you dont need to do the 4 bolt conversion. As far as the balancer, I was going to try to save some $$ for now and use the stock one, but the hub wouldnt fit the snout of my new crank, and the shop said they couldnt hone it since it is closed at one end. I ended up getting the ATI and they honed the hub to fit. I would check your stock one out, mine was showing signs of wear with only 53,000 miles on it.

 

I'm running the stock balencer with a Scat 9000 3.75 crank. Take the balencer and hub to the machine shop that balences the motor.

I'm running the stock 2bolt mains. Motors been together for 5 and 1/2 years, and seen lot's of spray, without a problem.

 

LT1 harmonic dampers are neutral balanced. Unless you feel the need to have it checked it does not need to be balanced to the rest of your rotating assy. I'd say you will be OK with the stocker, provided it fits.

Rich Krause

 

Don't see why not as long as it's in good shape. You can pick up a Powerbond for quite a bit less than a Fluidampr or ATI though.

 

I agree with Rich, You probably don't need it balanced with the crank but read on.

I just had this done with the SCAT 9000 crank and my machinist wanted the New Stock Balancer to balance the entire assembly.
The New Scat cranks needed lots of balancing and the spend a lot of extra time on this and got it down to 1.6 grams, he normally does 2 grams. Yes, the netural balanced stock balancer is the way to go. I only had a block and had to purchase a GM balancer, "OUCH" not cheep. A fluid balancer will NOT work!

Two bolt mains are acceptable. Look at a four bolt and see how much metal the bolt goes down into on the outside bolt. You will see it is not much. Two bolt mains have been spinning high rpms for decades. Most people have never seen the main caps break or distort nor a crank fail, it is usually the rods that fail.

Jim
PS: this crank spun so smooth in the block it was amazing! Too bad I can only spin it to 7K on a 1993 dumb computer! It will spin to 8.5 or 9k easly with the componets.

 

If they balance the assembly with the stock flex/fly and neutral front, the stock one will work fine. (as said already)

 

Thanks for all the replies guys, now I have piece of mind and I can still use my underdrive pulley although I think I will get a keyed hub from Thunder Racing just for a little insurance.