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Re: [T3] Timing Type 3 w/ 009 and twin carbs!


Hello-

> > _All_ 009's run too retarded at cruising conditions - only at WOT are
they
> > "okay."  They need a vacuum advance canister to do anything more.
>
> Shad -- do you actually mean "at high rpms" (or maybe "at high
> rpms + WOT") rather than simply *any* wide open throttle conditions?

Nope.


> Or
> do you mean something more complex, where it's good to have the timing
> relatively retarded when you have any high throughput or
> near-atmospheric-pressure conditions at the intake (i.e. wide open
> throttle)?

Kinda, yes.

At low/part throttle, cylinder pressures are lower and the burn takes
longer, so more advance is needed to compensate.

That's why all the OEMs used dual advance distributors - the centrifugal
part took care of the RPM-dependence and the vacuum part took care of the
manifold pressure dependence.  For VW, the second part usually contributed a
max of 8-12 degrees of additional advance.  That means that at low throttle
3000rpm, you have 40 degrees of advance.

When you have no vacuum canister, you set the centrifugal part to work with
WOT (better to be too retarded than too advanced).  So, you are constantly
running too retarded at low throttle, making engine temps higher, engine
life lower, and gas mileage poorer.

I wrote a bunch of VW Trends articles on this subject awhile ago... 2000?
2001 maybe?

Take care,
Shad Laws
LN Engineering - Aircooled Precision Performance
http://www.lnengineering.com

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