I'm building a 496 bbc and i'm going with the scat 9000 crank which is external,i need to know do i have to internally balance the motor' it's race only 13 to 1
6.385 rods and i'll be spinning it to 7300 rpm. what's the benefit of a internal balance motor

Less weight and you do not have all that counter weight to sling

Red,
The amount of weight will be the same no matter if it is internal or external balance. Actually, you generally have to use MORE weight in the rear counterweight as compared to the weight on the flywheel because it is closer to the rotating centerline.
All that being said and done, general consensus is that the crank flexes less when internally balanced and is easier on main bearings, especially # 2 & 4. But .. I cannot say that I have actually seen a difference. I know plenty of guys running externally balanced big blocks without having any problems. Most marine engines are externally balanced and even though they rarely see 7300 rpm they do run at 5000rpm for hours at a time under full load.
It will probably cost you a bundle to internally balance it if the crank was made as an external balance crank. Probably at least 3 slugs of heavy metal in each end. Maybe Mike Lewis will chime in, I think he uses a lot of those cranks.
Hope this helps,

My first question is if it is a race only 13.0+, 7000+ RPM deal why are you using a cast crank??
That said, you will have about $400 to $500 more in your "budget crank" to internally balance it at a guess :rolleyes:
I always prefer to internally balance a crank if possible but as Bill said the differences in the real world are slight.
You will see it in the mains on a high RPM engine but there are a lot of externaly balanced deals out there that live.
Here is some general info about balance to read on a slow Sunday that I have posted before but what the hell,,, you asked :D

This was in response to another question about balancing:
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.

thanks all for info i ran a scat 9000 sbc 400 crank up to 7500 rpm for years with out problem and trying to put my money where it counts like in afr heads,i already have a ATI extrenal balancer and didn't want to spend another 300 for new balancer,

As silly as this sounds, I have read somewhere of just internally balancing the snout end and externally balancing the flange end so a neutral balancer could be ran for that "Stealth" thing!!

pdq67