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Old 11-07-2008, 05:46 PM
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balancing act

Hey guys I have a 509 casting SBC 400 that I'm putting 5.7 rods in from a 99 vortec motor. Both motors are externally balanced with a flex plate counter weight. Is this going to match up??
The 350 has a bigger wieght but the 400 has a notched harmonic balancer wher material is removed to make up the difference.

Its gonna cost me an extra 200 bucks to get it balanced so I'd really like to knoe if this is gonna be ok or not if I don't get it balanced??

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Old 11-07-2008, 06:07 PM
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Quote:
Originally Posted by eatonde
Hey guys I have a 509 casting SBC 400 that I'm putting 5.7 rods in from a 99 vortec motor. Both motors are externally balanced with a flex plate counter weight. Is this going to match up??
The 350 has a bigger wieght but the 400 has a notched harmonic balancer wher material is removed to make up the difference.

Its gonna cost me an extra 200 bucks to get it balanced so I'd really like to knoe if this is gonna be ok or not if I don't get it balanced??
The 350 with a one piece rear seal has a small amount of external balance to make up for a little pad they took off the crank to make space for the new seal. It is otherwise an internally balanced engine, no where like the needs of a 400.

The 400 ran out of space inside the crankcase for counterweights heavy enough to offset the weight associated with the increased stroke and heavier pistons. So they moved the final balance outside the oil seals with an offset weight on the damper and another on the flywheel/flexplate. Both are required to bring a 400 crank into balance.

Stroker small blocks 383 thru 406 and beyond can be internal or external balanced depending upon the crank selection. Some stroker cranks are intended as external balance and others are internally balanced. You have to watch for this when you purchase the crank. Internal balance is achieved with either a higher density steel in the case of forgings or with Mallory Metal inserts to the counterweights. On the other side there are light weight rods, pistons, and pins. So when you go shopping you've got to walk in knowing all this to be able to sort out the right pieces, you can't depend on the guy at the other end of the phone or behind the counter to know this. It's nice when they do, but it's a disaster when they don't.

The best plan is to expect to balance the rotating/reciprocating assembly. It's money well spent and the result really takes a lot of load off the spinning parts as well as the block. Making the probability that your expensive parts will not end up being blasted thru the side of the engine some evening.

Bogie
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Old 11-08-2008, 07:42 AM
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The 350 with a one piece rear seal has a small amount of external balance to make up for a little pad they took off the crank to make space for the new seal. It is otherwise an internally balanced engine, no where like the needs of a 400.

This is incorrect and misleading. The amount of imbalance at the rear of the one-piece 350 crank is 23.4 oz/in (664 grams), very close to the 400 imbalance of 25.1 oz/in (712 grams) at the rear of the 400. Certainly not a small amount.


tom
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Old 11-08-2008, 07:49 AM
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Quote:
Originally Posted by eatonde
Hey guys I have a 509 casting SBC 400 that I'm putting 5.7 rods in from a 99 vortec motor. Both motors are externally balanced with a flex plate counter weight. Is this going to match up??
The 350 has a bigger wieght but the 400 has a notched harmonic balancer wher material is removed to make up the difference.

Its gonna cost me an extra 200 bucks to get it balanced so I'd really like to knoe if this is gonna be ok or not if I don't get it balanced??
Both motors are externally balanced, but the 350 is neutral balanced at the front. You will need to use the 400 balancer and flexplate/flywheel. Since your 400 is using different pistons and rods (the 5.7" rods from the Vor-Tec are longer than the 5.565" 400 rods, so you can't use the 400 pistons. There are pistons for the 400 that are designed to be used with the longer rods, I'm assuming you are using these.), you will want to have your engine balanced.

tom
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Old 11-08-2008, 06:17 PM
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Yeah I would agree, if you are going to be swapping all those parts you should do it right and have it balanced.
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Old 11-08-2008, 07:24 PM
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in the block

OK the balanceing is all ne ground for me I always just used stock parts.
So how do the do the balanceing?? Do they gotta assemble everthing in the block or what??
BTW a 406 is not a stroker, Its just bored +.030, it's still a 3.75 STOCK stroke.
I Probably will go ahead and get it balanced just to be safe, But is 48 grams a lot. (712-664=48)
I know it would be if it were in one spot but, But with if you divide it by 8 for the number of rods, It comes to adding 6 grams per rod. Is that how they would balance it or would they be adding to the balancer and flexplate??? Sorry if its a dumb question, but I'm really a stranger in this department...
Danny
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Old 11-08-2008, 07:42 PM
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Maybe this can shed some light on the subject for ya:

http://www.carcraft.com/howto/ccrp_0...ing/index.html


I used to do the balancing at our machine shop. Although, it would sometimes cause riffs with some customers, because they swore they never needed to have an engine balanced before and we highly suggested that it be done. I always have and will have any of mine balanced........stock or performance.........just my 2 cents.
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