[Saab_c900] Are new turbo overboost switches for 8V engines available?

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Craig's Saab C900 Site - 04 Feb 2006 05:36 GMT

Hiya,

Got a bit of an issue with the overboost switch in my 8V turbo. Has a big
vacuum leak and I think it's one of the reasons that the engine's not
running properly (and not starting at all currently). I've got a
replacement but it's turned out to be the one for 16 V engines and I'm
betting their pressure settings are different. 8-)

Saabsite.com has the 8V ones priced at a massive US$116! Seems a lot for a
small device but then if they're new, perhaps it's not so bad.

Are there any other sources of these switches (Saab # 8579963) as new
items that you know of? If I do need to get a new one, it'll be handy to
have some alternative sourcing info available.

In the meantime I'm going to try out the 16V version (Saab # 8594632) and
see if it'll help to solve the current problem(s).

Regards,

Craig.

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ShazWozza - 04 Feb 2006 14:22 GMT

> Hiya,
>
[quoted text clipped - 13 lines]
> In the meantime I'm going to try out the 16V version (Saab # 8594632) and
> see if it'll help to solve the current problem(s).

Craig, why can't you just use a generic adjustable Hobbes switch?

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Craig's Saab C900 Site - 05 Feb 2006 20:37 GMT

>Craig, why can't you just use a generic adjustable Hobbes switch?

What is a Hobbes switch? 8-)

Craig.

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ShazWozza - 05 Feb 2006 21:48 GMT

>>Craig, why can't you just use a generic adjustable Hobbes switch?
>
> What is a Hobbes switch? 8-)

A pressure operated switch. Some folks spell them Hobbes and some Hobbs. I
suppose it is the name of the guy who first designed one. Examples being
your overboost detector, oil pressure switch yadda yadda
If you are really stuck for a genuine Saab overboost switch I don't see why
you can't use one.

A common after market use for them is in boost sensors for controlling water
injection.

I think from memory either AutoSpeed.com or Silicon Chip have designs which
use them in various boost pressure related projects. I would check out
Oatley Electronics or Jaycar. I found this Sydney link here
http://www.coolingperformance.com/catalog/item/2246167/1692078.htm
they have a A$40 switch (no idea of the quality).

Hobbes switches come in various ranges of pressures and many can be
adjusted. It is also possible to use one with a lower pressure rating by
way of a restrictor (in which case you would need to calibrate the
restrictor hole carefully).

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Craig's Saab C900 Site - 06 Feb 2006 22:24 GMT

>> What is a Hobbes switch? 8-)

>A pressure operated switch. Some folks spell them Hobbes and some Hobbs. I
>suppose it is the name of the guy who first designed one. Examples being
>your overboost detector, oil pressure switch yadda yadda
>If you are really stuck for a genuine Saab overboost switch I don't see why
>you can't use one.

Ok thanks. I've found a few of them on Ebay. Seems that these generic items
have a threaded connection. I have no idea what the pressure settings for
the overboost switches used by Saab are, but there are a couple of these
'Hobbs' devices specifying 15 psi which sounds about right for an 8V non-APC
turbo engine, though I'm open to correction...

Craig.

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