Words of wisdom & experience!

Additional note: Obviously on that type of damper if the elastnomer fails the static and dynamic balance at the nose of the crankshaft, as well as the harmonics, are disrupted, with the results you experienced.

Grandpa always said. "It only costs a little more to go first class."

He also said...... "If you can't afford to do it right the first time, how much will it cost to do it over?"

OK....here is some more input on this issue. Some of what I am going to say has already been said.

Some engines, such as all SB Fords, 383 and 400 SB Chevys, and 454 and 502 BB Chevys, are externally balanced. What this means is that due to design limitations in the engine, they are unable to add enough weight to the crankshaft to bring it into balance. This is taken care of by adding weight on the damper and flexplate/flywheel. Because this weight is outside the engine, it is referred to as "external" balance.

Engine builders can convert external engines to internal by drilling holes in the crank and inserting an extra heavy metal called mallory metal. This is kind of expensive. Some crank manufacturers, like Eagle, have been able to redesign external style engine cranks so that they are internal.

In my opinion, if you can convert an externally balanced engine to internal, do it.

Here is where some of the confusion comes in. As several people have stated, on an externally balanced engine there is additional weight on the balancer and the flexplate. In the case of a stock balancer, this is achieved by cutting away, or scalloping as some have said, some of the weight off of the inertia ring which is the outer part of the damper. On the flexplate or flywheel, there will usually be a heavy weight tack welded to one area.

If you have a stock factory engine and want to switch balancers or flexplates you can do that without rebalancing the engine, as long as you use externally balanced dampers and flexplates on an externally balanced engine and neutral balanced dampers and flexplates on a neutral balanced engine.

Where problems start to arise is if you have a built engine and your engine balancer attempts to bring the entire assembly into balance by drilling holes or adding weight to either the damper or the flexplate or flywheel. If this has been done, then if you try to replace those components with new ones, your entire engine will be out of balance. Actually this is a no-no and no competent engine balance shop would do this.

As mentioned above, stock externally balanced dampers have a section of the inertia ring removed. Unfortunately this is a very bad deal if the rubber fails and the ring on the damper begins to rotate because it seriously throws the engine out of balance big time. If this happens while you are revving the engine up, it could throw the engine out of balance enough to break the crank. My company makes aftermarket performance dampers and we accomplish the external balance by using a bolt-in counterweight that bolts to the hub, not the ring. In this instance, if the ring should move, it does not affect the engine balance significantly.

In damper and flexplate/flywheel manufacturing, the units still have to be balanced irrespective of the added weight. By this I mean that the parts have to be balanced properly before the counterweights figure into the mix. With a bolt-in counterweight this is a simple task. The damper is spun on a balance machine and balanced by drilling holes in it. Then the counterweight is bolted in to provide the external balance.

With a factory style damper, they have to be bolted to a plate that has a counterweight on it to offset the counterweight on the damper when the damper is balanced.

So looking at your damper and flexplate/flywheel to see if they have balance holes drilled in them so you can determine if your balance shop has drilled them won't work. Because the manufacturer of the balancer and flexplate/flywheel will have drilled balance hole already. You might be able to tell if your balance shop has drilled additional holes because if the original part was painted, the new holes will show up.

I hope this information helps clear up some of these issues.

Internal means the crank can be balanced by itself
External means the crank has to have the balancer and flywheel to be balanced.

The internal engine will have no weights or very smal one on the flywheel and balancer. The external will have big weights on the flywheel and balancer.

On a blower motor you don't need a balancer. So BDS tells me. But you should use a crank with 2 keys 180 deg from each other and a billet drive hub.

http://blowerdriveservice.com/

Since we're yacking about balancing...heres my prefernce..

I like to run nuetral balanced engines...i/e..non SCB 400 stuff, why?

Well, this way I take my crank in and have it balanced...have the rods and pistons matched..be done with it.

Then I grab near ANY flywheel/pressure pate/flexplate/balancer I want, and run the darn thing.

This way when my flywheel/pressure plate/etc goes bad or needs to be replaced, i don't have to take the engine apart and have it all balanced as a unit again.

Seems simple to me..lives very well to 7K rpms (probaly more) and is simple to fix when you want it to.

Just some of my thoughts, hope it helps.

yes i have also heard that a balancer is not really a big issue with a blown motor, because of the belt that takes alot of the dampning. but i still need one to acatch my blower drive pulley off of, so i think i will go with a internal crank with a small damper, and have them balanced.

Controlled dyno tests have shown that a larger heavier damper actually makes significantly more power across the board and does not hinder 300*/sec acceleration rates, especially on SBC.

then how does a larger damper affect a supercharger that is running off of it?
im really curious about this

I'm not sure what your question means.

A damper's purpose is to suppress crankshaft twist and whip/ harmonics.

Use the largest performance damper, NON-rubber, that fits.