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internal / external balanced sbc

6K views 6 replies 6 participants last post by  motown/malibu 
#1 ·
I did a search to get an education on internal vs external balanced sbc stroker. Got info for the bbc. Does the same info apply to the sbc that is stroked? Can someone give reasons as to why someone would choose one over the other. Is an internal balanced stroked sbc a better choice vs external? Why? Thanks.
 
#2 ·
i think it is more a cost issue. it depends on which crank you chose to use for your build. if you buy an expensive steel crank for internal balance or use a stock 400 crank it will have to be external balance. Performance wise, i can't really tell you, but other than the difference in the strength of an expensive crank vs a stock one, i doubt there is much benefit.
 
#3 ·
Internal balance can be easier on the bearings and crankshaft, particularly at higher RPM.

It also costs more to convert from external to internal.

My 400 is internal balanced at the flywheel end, and external balanced at the damper end. I paid less than for a "full" internal balance, but I still can use cheap and available neutral-balanced flywheels.
 
#4 ·
I your going to run RPMs past 6,500 its best to go internally balanced. External balance the weight is at each end of the crank, flywheel and balancer. At higher RPM's say 7,000 it tends to stress the middle of the crank.

Internal balance if your going to RPM it, external for lower rpm 6500 under street strip.
 
#5 ·
Thanks for the information. So to sum it up external balance is less expensive, go with an internal balance if turning above 6500 rpm's. Is it really just that simple? Who makes a good external balanced rotating assembly for a 400 to 450 HP 383 stroked sbc or even an assembled short block for a decent price?
Thanks again.
 
#6 ·
Originally posted by deiinc:
Thanks for the information. So to sum it up external balance is less expensive, go with an internal balance if turning above 6500 rpm's. Is it really just that simple? Thanks again.
A little more to it than that in my opinion. I don't feel there is a magical RPM number to differentiate between when you internal or external balance an engine although I completely agree that the higher the RPM the more important it becomes.
The main reason for external balance is money & packaging.
It was simply a lot less expensive for the manufacturer to package the same engine with more cubic inches in the same confines with an external balance.

External means there is added weight on the damper or some other part that is on the front of the crank & a flywheel that has weight added to it.
Internal means there is enough counterweight in the crankshaft so this is not necessary.
I prefer internal as the closer you put the weight to where it is needed the more effective it is. It lessens a condition called couple which is a whole new discussion but essentially a condition where when you add weight some distance from where it should be it causes a "rocking" or "flexing" motion in the crank
This is not the twisting motion that the damper helps control, rather more of a "rock" from end to end.
External will work fine & is much less expensive in almost all cases where you need to add more weight.
It gets very expensive to add Tungsten (heavy metal) to the crank to internal balance an engine & is really not necessary for the majority of cases.
High RPM & endurance type engines would be an example of where you would want to spend the money on internal balance as external balance is somewhat harder on the bearings that are closest to the unbalanced part of the crank.

Now,,, all that said, there are a ton of engines running around out there quite happily that are externally balanced but in my opinion if possible I would always internally balance a performance deal. ;)
 
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