[TheMonkey]

If I understand correctly, stock Pontiacs were internally balanced, with a slightly off balance flex plate that can only bolt up a certain way.

Soooo.... why'd they do this? Why not just neutral flexplate and exact internal balance?

& the question for the machine shop guys... seems there are a lot of neutral flexplates for sale.... how many motors would you estimate are out there with a mismatched crank & flexplate? what is the effect of a neutral flexplate on a motor that should have a stock flexplate?

[Mr. P-Body]

Monkey,

The slight imbalance at the rear is about 6"-oz. It can be removed and the assembly "internally balanced" fairly easily. Internal balance is recommended for higher revving engines, to keep the harmonics INSIDE the bulkheads. This is why the aftermarket performance flywheels and flexplates are "nuetral". There ARE some "stock balance" SFI units available

Running a "nuetral" flexplate where the stock one is called for will create low-RPM vibrations and beat on the main bearings, particularly nos. 4 and 5.

Jim

[PONTIAC DUDE]

Actually with limited room for counterweights they had to go external. Ya got to remember that the longer the stroke and weight opposite the rod and crank has to be roughly the same spinning. Heavy pistons and cast rods dictate more counterweight. You can move it in sometimes but not often.

The reason you can get away with an internal balance on the back side with race stuff and no mallory is that you are using a lighter reciprocation assembly, such as lighter rods, pins pistons, etc.

[TheMonkey]

Thx.

sounds like they did it because it wouldn't physically fit inside, there is no advantage to stock setup, and when the assembly is light enough to have balance within the mains, that is recommended?

my arrangement is stock. it was balanced with the stock flywheel. is the downside to this a function of RPM only, not power? i'd suppose i'll rarely be over 5,200 and prob limit at 5,500. but power should be chunky at 525hp/600tq.

i'm not going to change my balance at this point, but what kind of rev ceiling should be observed with stock balance scheme? or.... is method of balance too small of a variable to really care at these levels?

[Mr. P-Body]

You will be fine to at least 6,500. One must always remember, a "high revving Pontiac" is not a high revving engine like a small block. We're talking 7,000-up.

Jim