If you look at Table 2 in Dr. Mohan's SAE paper titled "Comprehensive
Theory of Viscous Coupling Operation" you can see that the initial fill
ratio of the special fluid inside plays a huge role in the onset of the
hump state with just a 1% or 2% change in fill having a large effect.
This implies to me that overall pressure in the unit is a predominant
factor in VC performance. In fact around the world replacement VC
offerings have included options for fill capacity to tailor to specific
needs.

IMHO, in the distant past there have been some false assertions on the
Syncro list that led to misunderstanding of the VC behavior. Notably
this involved an assertion that the torque level involved in the hump
phase was higher that the engine was capable of and thus that hump phase
was not important to VC operation. This error arose from a failure to
account for the torque multiplying effects of the transmission in the
lower gears.

Mark

Alistair Bell wrote:
> I just posted another bit of viscous coupling blether on my blog.
>
> http://shufti.wordpress.com/2010/04/02/viscous-coupling-hump-condition/
>
> Trying to clear up the misunderstanding and misinformation, this time
> about the hump state, or 100% torque transfer.
>
> If any of you have good argument pro/con, please let me know. Its all
> pretty "academic" but I do liek to understand these things, and I
> have not been satisfied with the explanations I have read on this and
> that lists.
>
> cheers
>
> alistair
> '86 syncro 7 passenger
> '82 westy, diesel converted to gas in '94
> http://www.members.shaw.ca/albell/
> http://shufti.wordpress.com
>