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Old 10-10-2010, 05:50 PM
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BBC flexplate

alright i have a mid 80's 454 BBC with a scat crank...motor is 468....it has been balanced and all that, but i am currently running a 4 speed. i want to change over to a turbo 400 auto ...with the aftermarket crank is it still externally balanced?...and will it effect the rotating assembly since it wasn't balanced with it?....it is in a 86 chevy truck .....should i go with a heavier or stock weight flexplate.....thanks in advance

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Old 10-10-2010, 05:53 PM
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Scat cranks are available in internal or external balance. To be safe, send your new heavy duty flexplate along with stick flywheel yo balance shop and tell em "match er up". Simple stuff.
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Old 10-11-2010, 06:33 AM
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Quote:
Originally Posted by MUD MANIAC 44
alright i have a mid 80's 454 BBC with a scat crank...motor is 468....it has been balanced and all that, but i am currently running a 4 speed. i want to change over to a turbo 400 auto ...with the aftermarket crank is it still externally balanced?...and will it effect the rotating assembly since it wasn't balanced with it?....it is in a 86 chevy truck .....should i go with a heavier or stock weight flexplate.....thanks in advance
If the the damper is externally balanced, you need an external balanced flexplate (one w/a weight welded on to it). If the damper is neutral balanced (aka internally balanced), you need a neutral balanced flexplate.

The external balanced damper- if OEM- looks like:


454 BALANCER

Notice the 454 balancer's counterweight is located inside of the hub, unlike a 400 SBC, that has the outer ring scalloped:


400 SBC BALANCER

You can tell if the flywheel has been set up as an externally balanced unit just by inspecting it.

There is a chance the flywheel was drilled as part of the rotating assembly balancing operation, so it might not be a bad idea to have the flywheel and flexplate checked to see that the flywheel hasn't been altered.

If it HAS, as was already said, the flexplate needs to be matched to it. Hopefully that is not the case, otherwise you have to do this every time you change the flexplate/flywheel.

But most times, the flexplate or flywheel and balancer are left balanced "stock" to avoid such problems.
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Old 10-12-2010, 05:30 PM
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thanks for the info guys
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