Re: [T3] Too much advance

["Mark Seaton" <Markse@mo-sys.com>]

----- Original Message ----- 
From: "Jim Adney" <jadney@vwtype3.org>
To: <type3@vwtype3.org>
Sent: Tuesday, May 04, 2004 2:29 AM
Subject: Re: [T3] Too much advance



> > The scary thing is the total advance
> > figure which exceeds 45 deg with the vac attached at 3500 rpm which
seems
> > way too high.
>
> The thing that no one ever explains is that the 32-34 deg limit is the
full
> load limit or the limit that the racers have to worry about. When you're
> cruising along at 1/5 throttle at 50 MPH, you can tolerate MUCH more
advance,
> and the result is better gas mileage. You won't find this mentioned in any
of
> the high performance books because it's just in an operating area where
they
> never go.

The thing is I did a search for advance curves on the internet and though I
couldn't find any for ACVWs I did find some for other cars and none of them
came anywhere near to this much advance. I really need to complete my tests
to see the real figures.

> > I don't know how different that would be in actual driving conditions,
> > but I can't see why it should be any less.
>
> The difference is that there is no load on the engine in the tests you've
run.
> When you're actually out driving you'll have load, so you'll have to open
the
> throttle more, with no increase in RPM, so the air velocity past the
vacuum
> port will be less, and the vacuum will be less. I suspect that you'll find
that
> you almost never see any vacuum until you reach your desired speed and can
let
> up on the throttle.

That makes a lot of sense. I wonder why the engine runs seemingly better
with the hose disconnected. I'm wondering now if it has to do with the idle
being a bit low- could influence the vacuum starting point.

> > The mechanical advance itself is fairly nice and linear/ proportional
and
> > maxes out at a healthy 32ish degrees.
>
> Can I assume that includes the static advance?

Yes- 7.5deg strting advance.

> > I did notice that my idle was a little low at 850rpm.
> >
> > I will endeavor to do some more tests with a remote vacuum gauge and
tach
> > while driving in various conditions to complete the picture soon.

> Do you have a Bentley manual? It would be worthwhile studying the
distributor
> curves and coming to some kind of understanding of them and what they're
doing.
> What you're doing is just trying to produce the appropriate curves for
your
> dist.
>
> When studying the Bentley curves, note that they are all in distributor
shaft
> degrees; to get crankshaft degrees you have to multiply by 2.

(ashamed) no- not yet. They are a bit scarce over here. Do you have a copy I
could buy?

Thanks for all your help,
Mark


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