RE: Internal vs. External Balance

From: Ray Block (
Date: Sun Feb 28 2010 - 17:33:16 EST

> -----Original Message-----
> From:
> If I read what Ray (and others) are saying correctly, when
> replacing a 360 harmonic balancer or torque converter or flexplate,
> as far as the balance goes, the only differentiation is "318 vs 360"?
> That is, there aren't a whole bunch of different ones built with
> different balances so as to match the balance of your particular
> engine?


> If that is the case, I am assuming that although the 360 is
> "extermally balanced", the internal imbalance which requires this
> external balance is exactly the same for every 360, there is no
> variation from engine to engine?


> Assuming that I have understood correctly so far, rather than
> imbalance each engine the same, why the heck didn't they just build
> the 360 internally balanced in the first place? Seems like this would
> save a lot of money since all harmonic balancers, flexplates and
> torque converters could them be shared between the 318 and 360 with no
> interchange worries or the resulting confusion?

I gather it was cheaper to Externally balance the engines. I don't think
the factory worried much about interchangeability. Then again, its been my
experience that some engineers make changes just to justify their jobs. ;)

> Were the 360 rods and
> pistons simply too heavy to add enough weight to the crankshaft with
> the block clearance involved?

No. The rods are the same for all small block mopars. The 360 pistons s/b
lighter than the 340's since the bore is smaller. They are slightly larger
than 318 pistons. The 360, for some reason, has larger mains. Don't know
why unless it was perceived durability for the proposed applications and
because of the 360's longer stroke. Remember, the original 360 was offered
only in two-barrel form in 1971 and became the standard engine instead of
big blocks in heavy cars from '71 up. Torque was the apparent goal. They
first became available as performance engines in the '74 model year
utilizing the 340 cams when the short stroke 340's were
discontinued...perhaps due to emissions. I've read that large bores and
short strokes are not emissions friendly. ??


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